simplified middle school chemistry for std viii

New Simplified Chemistry Class 8 ICSE Solutions – Carbon & Its Compounds

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Simplified ChemistryChemistryPhysicsBiologyMathsGeographyHistory & Civics

EXERCISE

Question 1.
Differentiate between the two branches of chemistry – organic chemistry & inorganic chemistry with suitable examples.
Answer:

• Organic chemistry : “A branch of science that deals with the study of specific compounds (of carbon) hydrogen and oxygen.”
  e.g. methane CH₄, ethane C₂H₆, CH₃COOH, CH₄OH methyl alcohol.
• Inorganic chemsitry : “A branch of science that deals with the study of – oxides of carbon, carbonates, metallic carbides etc.”
  e.g. H₂C0₃ – carbonic acid, C0₂, CaC0₃ calcium carbonate.

Question 2.
State how carbon occurs in the free state and in the combined state.
Answer:

• Occurence of carbon : In free state – diamond, graphite, in impure form as coal.
• In combind state : C0₂ in atmosphere, hydro-carbon as natural gas, petroleum, cellulose in wood and limestone CaC0₃.

Question 3.
Define the term ‘allotropy’. Give a reason why carbon exhibits allotropy.
Answer:
Allotropy : “The phenomenon of occuring of an element in two or more forms having same chemical properties but different physical properties.”
Carbon shows allotropy as a result of – difference in atomic arrangement in the crystal structure.

Question 4.
Name two crystalline and four amorphous allotropes of carbon.
Answer:
Allotropes of carbon:

Crystalline :

1. diamond
2. graphite.

Amorphous :

1. coal,
2. coke
3. lampblack
4. wood charcoal.

Question 5.
Compare the structure of the crystal of diamond & graphite with special reference to the reason for diamond being the hardest natural substance while graphite one of the softest. Compare the electrical & thermal conductivity of the two crystalline allotropes of carbon.
Answer:

• Structure of crystal of diamond : Hardest natural substance is due to – strength and uniformity of the carbon – carbon covalent bond [tetrahadron structure].
  It is bad conductor of electricity and heat due to abscence of free electrons in the crystal, i.e. no electron is free to move.
• Structure of graphite : “Is soft and greasy due to parallel layers of C-atoms held together by weak VANDER WAAL – forces which slide over one another, i.e. hexagonal structure.
  It is good conductor of heat and electricity due to – presence of mobile electrons in the crystal.

Question 6.
With reference to the structure of the two crystalline allotropes of carbon, state why diamond is inert or unreactive while graphite is comparably more reactive.
Answer:
Structure of diamond is compact and hence unreactive. Graphie has open structure and more prone to chemical attack.

Question 7.
State the reasons for (a) Use of diamond – as an. item of jewellery, (b) Use of graphite – (i) as a lubricant for heated machine parts, (ii) as a lining for crucibles used in manufacture of high grade steel, (iii) as an electrode in electroplating.
Answer:
(a) Use of diamond – as an item of jewellery as – diamond has sparkling brilliance due to high refractive index is cut and polished.

(b)

1. Heavy machines which run very fast, when other lubricants are used catch fire, but graphite as lubricant when used parallel layers slide over one and other is non-volatile and non-sticky and reduces friction between rotating parts.
2. Graphite is used in refractory crucibles as graphite can withstand high temperature is a good conductor of heat.
3. Graphite as electrode in electroplating as graphite is good conductor of electricity relatively inert and almost does not react with acids.

Question 8.
State in brief the transformation of vegetable matter to different types of coal varying in carbon content. State two uses each of

(a) coal
(b) coke
(c) lampblack or soot.

Answer:
Transformation of vegetable matter to coal is due to slow bacterial decomposition of vegetable matter under the influence of heat from within the earth, high pressure of earth (soil) above it and in absence of oxygen over millions of year.
The different stages of transformation of vegetable matter results in different types of coal

1. 60%C is peat
2. 65%C is lignite
3. 85%C is bituminous
4. 90%C is anthracite

Question 9.
‘Wood charcoal – an amorphous aliotrope of carbon reduces heated metallic oxides to metals.’ Give a balanced equation to support the statement.
Answer:
Wood charcoal reduces ZnO, Fe2O₃ to metal.

Question 10.
Carbon dioxide occurs both in the free state and in the combined state.
State three methods how carbon dioxide is added to the atmosphere.
Answer:
Carbon dioxide is added to the atmosphere by

1. Burning of carbon compounds – wood petroleum.
2. Death and decay of organic matter.
3. Respiration in living organisms.

Question 11.
In the laboratory preparation of carbon dioxide by action of a dilute acid on a metallic carbonate give – (a) A balanced equation for the preparation (b) A reason for (i) use of a washer bottle containing cone. H₂SO₄ in the preparation (ii) Not collecting the prepared gas over water (iii) Not using dilute sulphuric acid as a reactant in the preparation.
Answer:

(b)

1. Cone. H₂SO₄ used in washer bottle absorbs moisture from the gas.
2. C0₂ is soluble in water and hence is not collected over water.
3. Dil. sulphuric acid is not used as reactant. Since H₂SO₄ reacts with calcium carbonate forming- a coating of insoluble calcium sulphate [CaSO₄]. The reaction slowly comes to a stop.
   

Question 12.
How would you prove experimentally that

(a) Carbon dioxide does not support combustion
(b) Is slightly acidic in nature.

Answer:
(a) Carbon dioxide does not support combustion.

• Experiment : Bring a burning candle in a gas jar full of CO₂ gas. The candle is extinguished. This shows that CO₂ is non-supporter of combustion.
  

(b) CO₂ gas is acidic in nature. Bring a moist blue; litmus paper in the mouth of gas jar full of CO₂ gas. The blue colour of filter paper changes red. This shows that CO₂ gas is acidic in nature.

Question 13.
Starting from carbon dioxide how would you obtain

(a) A weak acid
(b) A fertilizer
(c) A highly poisonous gas
(d) Black particles of carbon.

[Give balanced equations for the same]
Answer:

(a) Carbonic acid from CO₂ : when CO₂ is dissolved in water, carbonic acid is formed.

(b) CO₂ reacts with ammonia gas to form urea (a nitrogenous fertilizers).

(c) CO₂ is reduced to a highly poisonous gas CO by carbon (coke).

(d) Black particles of carbon : Burning magnesium burns in CO₂ making use of oxygen of CO₂ producing black carbon particles.

Question 14.
State how you would convert carbon dioxide to a metallic carbonate using a basic oxide e.g. sodium oxide. [Give a balanced equation]
Answer:
Basic oxide like Na₂O by CO₂ are converted into carbonate.
Na₂O + CO₂ → Na₂CO₃

Question 15.
‘When carbon dioxide is bubbled into lime water, the lime water turns milky and when bubbled in excess the milkiness disappears’. Give balanced equations to support the statement.
Answer:

When CO₂ is passed in excess, milkiness disappears due to formation of bicarbonate which is soluble in water.

Question 16.
Explain the term ‘dry ice’. State its application. Give three reasons why carbon dioxide finds application in fire extinguishers.
Answer:

• Dry ice : Solid carbon dioxide is called dry ice.
• Applications : Dry ice is used as refrigerant for preservation of foods as it freezes faster and lasts longer than ordinary ice.

Question 17.
Using a magnesium ribbon, how would you prove that a given gas jar contains carbon dioxide.
Answer:
It is a test to find gas in the jar is carbon dioxide. On burning magnesium ribbon in a jar of carbon dioxide.

Mg bums in CO₂ gas depositing – black particles of carbon on the walls of the jar. If black particles are found on the walls of jar, it is carbon dioxide gas.
_CO2 + 2Mg → 2MgO + C

Question 18.
State the function of cone, sulphuric acid in the laboratory preparation of carbon monoxide from oxalic acid.
Answer:
Function of cone, sulphuric acid is to remove molecules of water from formic acid i.e. it acts as dehydrating agent.

Question 19.
Give reasons why carbon monoxide is considered a highly poisonous gas. State why it is dangerous

1. To sleep in a closed room with a fuel burning
2. To be in the vicinity of smokers.

Answer:
Carbon monoxide is highly Poisonous gas : Carbon-monoxide combines with haemoglobin oxygen cariying capacity of blood is decreased

1. In a room which is closed and coal fire produces CO in limited supply of oxygen as room is closed. The haemoglobin combines with CO to form carboxy- -haemoglobin and oxygen carrying capacity decreases which causes death.
2. To be in vacinity of smokers : The fumes of – burning tobacco contains traces of carbon monoxide.

Question 20.
Convert carbon monoxide to carbon dioxide using two different methods.
Answer:
Methods of converting CO to CO₂.

1. CO bums in oxygen and changes to C02.
   
2. By reducing metal oxide.
   ZnO + CO → Zn + CO₂

Question 21.
State how carbon monoxide finds application in

1. The metallurgy of iron
2. Preparation of an alcohol.

[Give balanced equations for the same]
Answer:

1. CO is used to extract iron metal from its oxide as it reduces heated metal oxide.
   
2. Preparation of alcohol :
   
   

OBJECTIVE TYPE QUESTIONS

Q.1. Name the following :

Question 1.
A crystalline allotrope of carbon built up from a hexagonal unit.
Answer:
Graphite.

Question 2.
An allotrope of carbon used for the manufacture of coke.
Answer:
Coal.

Question 3.
An amorphous allotrope of carbon which floats on water.
Answer:
Wood charcoal.

Question 4.
An acid formed when carbon dioxide is dissolved in water under pressure.
Answer:
Carbonic acid.

Question 5.
The gaseous product obtained when carbon monoxide is passed over heated iron (III] oxide.
Answer:
CO₂ [Carbon dioxide].

Q.2. Select the correct answer from A, B, C, D & E for each statement given below :
A : Anthracite
B : Diamond
C : Carbogen
D : Urea
E: Lampblack

Question 1.
An allotrope of carbon used as a tip for deep boring drills.
Answer:
B : Diamond

Question 2.
The type of coal with the highest carbon conent.
Answer:
A : Anthracite

Question 3.
An allotrope of carbon obtained by burning kerosene oil in a limited supply of air.
Answer:
E : Lampblack

Question 4.
A nitrogenous fertilizer obtained from carbon dioxide.
Answer:
D : Urea

Question 5.
A compound which finds use for a victim of carbon monoxide poisoning.
Answer:
C : Carbogen

Q.3. Give a balanced equation for the following conversions : [In one or two steps]

Question 1.
Coke to water gas.
Answer:
Steam is passed over white hot coke at 1000°C

Question 2.
Calcium bicarbonate to calcium nitrate using a dilute acid.
Answer:
Calcium bicarbonate to calcium nitrate

Question 3.
Lime water [soln. of calcium hydroxide] to calcium bicarbonate.
Answer:
Lime water to calcium bicarbonate
When CO₂ is passed it turns milky.

Question 4.
Carbon dioxide to carbon.
Answer:
CO₂ to carbon
On burning magnesium in CO₂

Question 5.
A metallic oxide to calcium carbonate.
Answer:
A metallic oxide to calcium carbonate

Q.4. Complete the statements by filling the blanks with the correct word from the bracket.

Question 1.
The crystal of ___ [diamond/graphite] is opaque to light and is a good conductor of heat.
Answer:
The crystal of graphite is opaque to light and is a good conductor of heat.

Question 2.
A graphite-clay mixture baked at high temperature is used in making ___ [lubricants/refractory cruscibles].
Answer:
A graphite-clay mixture baked at high temperature is used in making refractory cruscibles.

Question 3.
Adsorption capacity of wood charcoal is increased by passing ___ [carbon dioxide/steam] over wood charcoal, at high temperature.
Answer:
Adsorption capacity of wood charcoal is increased by passing steam over wood charcoal, at high temperature.

Question 4.
___ [organic/inorganic] Chemistry is the Chemistry of carbon compounds mainly of ‘Carbon’, ‘Hydrogen’ & ‘Oxygen’.
Answer:
Organic Chemistry is the Chemistry of carbon compounds mainly of ‘Carbon’, ‘Hydrogen’ & ‘Oxygen’.

Question 5.
Sodium oxide combines with carbon dioxide to give ___ (sodium carbonate/sodium bicarbonate].
Answer:
Sodium oxide combines with carbon dioxide to give sodium carbonate.

Q.5. Give reasons for the following :

Question 1.
Diamond & graphite are allotropic modifications of carbon.
Answer:
Both diamond and graphite are carbon element, differ only in physical state and properties. Both on burning form CO₂ and nothing is left.

Question 2.
It is dangerous to stand behind a running engine of a vehicle.
Answer:
Running engine of a vehicle produces carbon monoxide which is dangerous for us.

Question 3.
Both CO₂ & SO₂ turn lime water milky. Moist potassium permanganate paper, helps in distinguishing the two gases.
Answer:
SO₂ gas moist potassium permanganate paper turns purple to colourless when comes in contact with sulphur dioxide gas where as CO₂ gas has no effect.

Question 4.
Carbon monoxide and not carbon dioxide is a highly poisonous gas.
Answer:
CO is highly poisonous combines with haemoglobin of R.B.C. and reduces the oxygen carrying capacity and death results.

Question 5.
Lime water finds application for testing both carbon dioxide & carbon monoxide gas individually.
Answer:
CO carbon-monoxide when passed through lime water, does not produce milkiness where as CO₂ produces milkiness in lime water and hence is used to test CO and CO₂.

New Simplified Chemistry Class 8 ICSE Solutions – Water

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Simplified ChemistryChemistryPhysicsBiologyMathsGeographyHistory & Civics

EXERCISE

Question 1.
Name a ‘pure form’ and an,‘impure form’ of water in the natural state.
Answer:
Rain water – pure natural water.
Sea water, lake water – impure form of natural water.

Question 2.
State what is potable water. Give its qualities or characteristics which make it fit for human consumption.
Answer:
Potable water : “That water which is fit for human consumption and for drinking purposes.”
Characteristics of potable water :

1. Water should be free from harmful bacteria, germs, suspended impurities and harmful salts.
2. Should be clear, colourless and odourless.
3. Should contain small amounts of dissolved gases and minerals for good taste.
4. Should have dissolved air and salts of (Na, Ca, Mg) which impart taste to the water and are useful for metabolic functions of the human body.

Question 3.
Give a reason why water is called a ‘universal solvent’ but, an alkali is not.
Answer:
Water is a polar covalent compound. When it comes in contact with any substance it breaks the electrostatic forces holding the molecules of that substance. Thus, the molecules break loose from the substance and hence dissolve in water. Thus, water is called a universal solvent and an alkali is not.

Question 4.
Name the solute, solvent & solution in the statement – ‘sodium chloride dissolves in water to give sodium chloride solution’. Define each of the terms in italics.
Answer:

• Solute (sodium chloride) : The substance which dissolves or disappears in solvent, i.e. liquid to form a solution.
  Mostly solvent is which is in less quantity.
• Solvent (water) : The substance which allows the solute to dissolve in it. It is the substance which is in more quantity.
• Solution (sodium chloride solution) : The homogenous mixture of solute and solvent is called solution.

Question 5.
Explain how each of the following factors affects the formation of a solution

(a) Proportion of the solute & the solvent
(b) Particle size of the solute
(c) Temperature of the solvent

Answer:
Factors effecting the formation of solution :

(a) Proportion of solute & the solvent : The solute must be in a small amount compared to the solvent which must be in much greater amount to dissolve the solute.
(b) Particle size of the solute : Smaller the size of solute, quickly and completely they will dissolve and form solution.
(c) Temperature of the solvent : Sometime increase in temperature makes the solution quicker.

Question 6.
Define the term ‘solubility ’ of a solute in water. If 10 g. of a solute is added to 100 g. of water at 50°C and stirred, it is seen that the total solute dissolves at that temperature giving an unsaturated solution. Is 10 g, the solubility of the solute in water. Give reasons.
Answer:
Solubility is the maximum amount of solute in grams – that will saturate 100 g of water at 0°C.
OR
Maximum amount of solute that can be dissolved in 100 g of solvent at specific temperature.
No, 10 g is not solubility as the solution is unsaturated and not saturated solution. This means more of solute can be added to make it saturated solution.

Question 7.
Give a reason why – (a) Alcohol and water form a miscible mixture while oil & water do not. (b) Boiled water tastes flat, (c) On opening a bottle of soda [carbon dioxide dissolved in water] the gas escapes out with a ‘fizz’.
Answer:

(a) Alcohol and water form miscible mixture as alcohol is soluble in water. Oil does not dissolve in water form immiscible mixture.
(b) Boiled water loses the gases and mineral and the water tastes flat.
(c) Solubility of gases in liquid decreases on decreasing the pressure and CO₂ come out of water with a ‘fizz’ when pressure decreases on opening the bottle.

Question 8.
Give the importance of

(a) Dissolved minerals & salts
(b) Dissolved air – in water.

Answer:
Importance in water of:

(a) Dissolved minerals & salts : Provide taste to water and are useful for metabolic functions of the human body.
(b) Air : Air containing various gases gives taste to water.

Question 9.
How are solutions generally classified. What is the basis of this classification.
Answer:
Solutions are classified into :

(a) True solutions.
(b) Colloidal solution.
(c) Suspensions.

The basis of classification is the size of dissolved or dispersed particles in the medium.

Question 10.
Draw a table to differentiate – True solutions, colloidal solutions & suspensions – with respect to

1. Type of mixture
2. Solute particles in the mixture.

Answer:
True solution :

1. Homogeneous mixture.
2. Particles are extremely small less than 1 nm in diameter = 10^-9 m.

Colloidal :

1. Appears to be homogeneous actually it is heterogeneous
2. Between 1 nm and 100 nm in diameter.

Suspension :

1. Heterogeneous mixture.
2. Size larger than 100 nm in diameter. Quite large size.

Question 11.
Give four examples of each of the above types of solutions i.e. true solution, colloidal solution & suspension. Give a reason why a true solution does not exhibit ‘Tyndall effect’.
Answer:
Examples of :

(a) True solution : Salt solution, vinegar, copper sulphate solution, sugar in water solution, air, brass.
(b) Colloidal solution : Milk, ink, blood, soap solution, starch sol.
(c) Suspension : Milk of magnesia, flour in water, chalk- water solution, muddy water. A true solution cannot exhibit ‘Tyndall effect’ because ‘the size of particles is very small and cannot reflect light falling on them.”

Question 12.
If 5 g. of a solute is added to 50 ml. of a solvent at a particular temperature and the solution can dissolve more of the solute at that temperature – is the solution obtained a saturated or an unsaturated solution. Give reasons.
Answer:
As more of solute can be dissolved at that temperature, it is unsaturated solution because saturated solution cannot dissolve any more quantity of solute at a particular temperature.

Question 13.
Explain the meaning of the term ‘saturated solution’. State two methods to convert a saturated solution to an unsaturated solution.
Answer:
Saturated solution : “A solution in which no more solute can be dissolved at that temperature, is called saturated solution.”
Two methods to convert a saturated solution into unsaturated solution are :

1. By increasing temperature
2. By increasing the amount of solvent.

Question 14.
State how a ‘supersaturated’ solution differs from a ‘saturated solution’. State briefly how you would prepare a supersaturated solution using potassium chloride and water.
Answer:
Super saturated solution contains more amount of solute than saturated solution in hot solution. On cooling, it gives out excess salt which separate out.
Preparation of supersaturated solution of potassium chloride in water : Take 100 g of water and add little by little of KCl salt and stir it, if it gets dissolved, add a little more and stir it. We find that 35 g of KCl can make the solution saturated at 20°C. Now heat the saturated solution and add more of KCl. At 40°C it will dissolve 40 g and 46 g at 60°C and 54 g at 80°C. This super saturated solution at 80°C. On cooling this super saturated solution excess of solute [KCl] crystals separates out.

Question 15.
The process of separation or deposition of crystals from a hot saturated solution on gentle cooling of the solution is called ‘crystallisation’. With reference to the statement explain what is meant by ‘water of crystallisation’. State which physical properties of a crystal are correlated with the water of crystallisation.
Answer:
Water of crystallisation is the number of water molecules that combine chemically – in definite proportion with the – concerned salt in the crystalline state.
OR
Some salts, while crystallising out from their solutions unite with a definite quantity of water, which is known as water of crystallisation.
Physical properties are that crystals are solid, definite regular shapes.

Question 16.
Differentiate between ‘hydrated’ & ‘anhydrous’ crystals. Give the chemical formula of – the following hydrated crystals –

(a) Washing soda
(b) Gypsum
(c) Blue vitriol
(d) Epsom salt
(e) Glauber’s salt. State

which crystal from (a) to (e) is a pentahydrate.
Answer:
Hydrated crystals : Contain definite number of water molecules in loose chemical combination with the crystals.
Anhydrous crystals : Do not contain any definite number of water molecules – in loose chemical combination with the crystals.

Formula of hydrated crystals :

(a) Washing soda : CaCO₃10H₂O
(b) Gypsum : CaSO₄.2H₂0
(c) Blue vitriol : CuSO₄.5H₂0
(d) Epsom salt : MgSO₄.7H₂0
(c) blue vitriol [CuSO₄.5H₂0] is a pentahydrate.

Question 17.
Differentiate between an efflorescent, deliquescent & ‘ hygroscopic substance with suitable examples.
Answer:
Efflorescent substances :

1. Lose wholly or partially their water of crystallisation when exposed to air.
2. Become powdery.
3. Washing soda CaCO₃.10H₂O, Gauber’s salt
   
4. Crystalline when hydrated.

Deliquescent substances :

1. Absorb moisture from atmosphere, absorb water and dissolve in it forming a saturated solution.
2. Deliquescence is maximized in dry conditions,
3. NaOH, KOH, CaCl₂, MgCl₂, FeCl₃ are the examples.
4. They are crystalline water soluble.
   FeCl₃ → FeCl₃ [Crystal changes to Solution]

Hygroscopic substances :

1. They are amorphous solids or liquids.
2. Absorb moisture from the air of atmosphere.
3. Do not change their original state.
   CaO (quick lime), cone. H₂SO₄, P₂O₅ and silica gel are the examples.
   
   (State not changed)
   is used for drying gases in laboratory.

Question 18.
Differentiate the function of concentrated sulphuric acid as a drying agent & as a dehydrating agent. Is fused calcium chloride a dehydrating or a desiccating agent. Give reasons.
Answer:
Sulphuric acid (cone.) acts as drying agent when it removes water from other substances i.e. for drying gases.
Cone, sulphuric acid acts as dehydrating agent when it removes chemically combined water from compounds due to it strong affinity for water.

Cone. H₂SO₄ has removed H₂0 from ethanol and changed it to ethene. Fused calcium chloride [CaCl₂] is desiccating agent as it is drying the substance.

Question 19.
Give a reason why metals are arranged in a series called – ‘activity series of metals’. Name a metal which reacts
with

(a) Cold water
(b) Boiling water
(c) Steam to liberate hydrogen in each case.

Answer:
Metals arranged in series is called ‘activity series of metals’ because metals differ in tendency to lose valence electrons and can be arranged in a series, i.e. metals are arranged in decreasing order of their reactivity. The most reactive metal at top of the series and then with decreasing reactivity.
Metal that react with

(a) Cold water – Sodium

(b) Boiling water – Magnesium [Mg]
(c) Steam – Iron [Fe]

Question 20.
Differentiate between – (a) Hard & soft water (b) Temporary & permanent hard water – with suitable examples.
Answer:
(a) Hard water : It does not lather readily with soap and soap is wasted.
Soft water : Soft water form lather easily with soap.

(b) Temporary hard water : contains bicarbonate of calcium or magnesium. Hardness can be removed by boiling water.
Permanent hard water : contains sulphates or chlorides of calcium and magnesium. Hardness cannot be removed by boiling water.

Question 21.
Give balanced equations to show how – (a) Temporary hardness enters into water, (b) Temporary hardness in water can be removed by boiling, (c) Permanent hardness in water can be removed by addition of washing soda.
Answer:

(a) Temporary hardness : Enters in water when rain water containing CO₂ falls on earth and combines with limestone [CaCO₃] & magnesite [MgCO₃] layers forming respective soluble bicarbonates.

(b) To remove temporary hardness by boiling : Bicarbonate changes to insoluble carbonate and water becomes soft.

(c) Removal of permanent hardness in water by adding washing soda : CaCl₂ or CaSO₄ present in permanent hard water exchanges the ions and forms CaCO₃ which being in soluble can be filtered.

OBJECTIVE TYPE QUESTIONS

Q.1. Select the correct answer from A, B, C, D & E for each statement given below :
A : Colloidal
B : Fused calcium chloride
C : Solvent
D : Suspension
E : Washing soda

Question 1.
The medium of dissolution which allows the solute to dissolve in it.
Answer:
C : Solvent

Question 2.
A solution which can pass through a filter paper but not through a semipermeable membrane.
Answer:
A : Colloidal

Question 3.
A decahydrate crystal.
Answer:
E : Washing soda

Question 4.
A drying agent placed in desiccator.
Answer:
B : Fused calcium chloride

Question 5.
A heterogenous mixture of undissolved particles in dispersion medium, visible to the naked eye.
Answer:
D : Suspension

Q.2. Give a balanced equation for the following conversions :

Question 1.
Calcium sulphate in permanent hard water to calcium carbonate using sodium carbonate.
Answer:

Question 2.
Iron to triiron tetroxide using steam.
Answer:

Question 3.
Sulphur dioxide to sulphurous acid using a neutral liquid.
Answer:

Question 4.
Potassium oxide to a strong alkali.
Answer:

Question 5.
Magnesium bicarbonate in temporary hard water to magnesium carbonate by boiling.
Answer:

Q.3. Complete the statements by filling the blanks with the correct word from the bracket.

Question 1.
Solubility of most solids ___ [decreases/increases] with rise in temperature.
Answer:
Solubility of most solids increases with rise in temperature.

Question 2.
Kerosene & water form a ___ [miscible / immiscible] mixture.
Answer:
Kerosene & water form a immiscible mixture.

Question 3.
Solubility of a solute is the ___ [minimum/maximum] amount of solute that will saturate 100 g. of water at t°C.
Answer:
Solubility of a solute is the maximum amount of solute that will saturate 100 g. of water at t°C.

Question 4.
Hygroscopic substance absorb moisture from the atmosphere & ___ [do not change/change] their original state.
Answer:
Hygroscopic substance absorb moisture from the atmosphere & do not change their original state.

Question 5.
The ratio of hydrogen & oxygen in water is ___ [2 : 1/ 1 : 2].
Answer:
The ratio of hydrogen & oxygen in water is 2 : 1.

Q.4. Give reasons for the following :

Question 1.
All solutions are homogenous mixtures of a solute in a solvent.
Answer:
Because solute dissapears in solvent and uniform composition throughout.

Question 2.
Hardness in temporary water can be removed by boiling, but hardness in permanent hard water cannot.
Answer:
Temporary hardness is due to the presence of bicarbonate of calcium or magnesium, on boiling bicarbonate decomposes to CO₂, carbonate which is in soluble and can be filtered out. Where as permanent hard water contains [SO₂]^2- or Cl^–– of calcium and magnesium, cannot be removed by boiling.

Question 3.
Colloidal solutions exhibit brownian movement.
Answer:
Particles in colloidal solutions do not settle down and are always in motion.

Question 4.
The percentage of oxygen, in air dissolved in water, is higher than the percentage of oxygen in ordinary air.
Answer:
Oxygen dissolves in water and in air there are some other gases also which make the bulk of air. Some gases dissolve in water.

Question 5.
Washing soda can be used to remove both temporary and permanent hardness in water.
Answer:
Washing soda Na₂CO₃ exchanges ions [SO₄]^– and Cl^– and do not make water hard.

Q.5. Match the substances in List I with the appropriate answer in List II.

Answer:

New Simplified Chemistry Class 8 ICSE Solutions – Hydrogen

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Simplified ChemistryChemistryPhysicsBiologyMathsGeographyHistory & Civics

EXERCISE

Question 1.
State how hydrogen occurs in the free state. Name three compounds containing hydrogen in the combined state.
Answer:

• In free state : In traces in the earth’s crust and atmosphere and in volcanic gases. It is also found in huge amount in the interior of the sun.
• In combined state : In organic compounds, plant and animals, in acids, in water.

Question 2.
Starting from zinc how would you obtain hydrogen using

(a) Steam
(b) A dilute acid
(c) An alkali

[ Give balanced equations for each & name the product formed in each case other than hydrogen]. Name a metal which will not react with the reactants above to give hydrogen.
Answer:
To obtain hydrogen using :

(a) Steam : Metals above [H] in activity series of metals, i.e. Zn, Fe and Pb react with steam and form corresponding oxides.

Metals below [H] do not react even with steam. Metal are Cu, Hg, Ag, Pt and Au.
(b) With dil. acids : Metals like Zn, Fe, Pb form corresponding salt.

Cu and metals below Cu do not react with dil. acids.
(c) An alkali : Zn, Pb react with concentrated alkali on boiling to give the corresponding metallic salt and liberate hydrogen.

Question 3.
‘Hydrogen is obtained by electrolysis of acidified water’. Answer the following pertaining to the preparation of hydrogen by electrolysis, (a) The meaning of the term ‘electrolysis’ and ‘electrolyte’, (b) Name the electrode –

1. through which the current enters the electrolyte.
2. at which hydrogen is liberated.

Answer:

(a) Electrolysis : “Dissociation of water into hydrogen gas and oxygen gas by the passage of electric current is called electrolysis.”

• Electrolyte : “A chemical compound (water) in solution state which conducts electric current and decomposes is called electrolyte.”

(b)

1. Electrode through which current enters the electrolyte is anode.
2. Electrode at which hydrogen is liberated is cathode.

Question 4.
In the laboratory preparation of hydrogen from zinc & dilute hydrocholoric acid – state a reason for

(a) Addition of traces of copper [II] sulphate to the reaction medium
(b) Collecting the hydrogen by downward displacement of water and not air & collecting it after all the air in the apparatus is allowed to escape
(c) Having the end of the thistle funnel dip below the level of the acid in the flask.

Answer:

(a) Addition of traces of copper [II] sulphate acts as catalyst and speeds up the reaction.
(b) Hydrogen is collected by downward displacement of water as it is slightly soluble in water and in air it form explosive mixture with air and also hydrogen is lighter than air.
(c) Otherwise the gas formed will escape through thistle funnel.

Question 5.
In the industrial method of preparation of hydrogen by the Bosch process – give

(a) Balanced equations for the first two main steps in the production of hydrogen
(b) The reason for use of addition of a promoter to the catalyst in the final step
(c) The name of the solution which absorbs the unreacted carbon monoxide.

Answer:
(a) Bosch process for industrial production of hydrogen :

• Step [I] : Preparation of water gas [CO + H₂] by passing steam over white hot coke.
  
• Step [II] : Reduction of steam to hydrogen by carbon monoxide.
  

(b) Promotor Cr₂O₃ is used to increase the efficiency of catalyst [Fe₂O₃].
(c) Ammoniacal cuprous Chloride [CuCl] solution absorbs unreacted CO.

Question 6.
State the following pertaining to the physical properties of hydrogen :

(a) Colour & odour
(b) Solubility in water
(c) Effect on moist blue litmus paper.

Answer:

(a) Colour and odour of hydrogen gas colourless. Odourless.
(b) Slightly soluble in water.
(c) No-effect i.e. colour does not change.

Question 7.
Draw neat labelled diagrams for two different experiments to prove that – hydrogen is lighter than air.
Answer:

1. To show that H₂ is lighter than air :
   
   
2. Air from jar B being heavier runs down in jar A and H₂ runs to jar B as it is lighter than air and burns with ‘pop’ sound in jar B if a burning splinter is brought there.

Question 8.
Starting from hydrogen gas how would you obtain

(a) A neutral liquid
(b) A basic gas
(c) A metal by reduction of its heated oxide.

[The metal formed is above iron in the activity series]
Answer:

(a) Hydrogen bums quietly in oxygen to produce water (a neutral liquid)
2H₂ + O₂ → 2H₂0
(b) 3 volumes of H₂ react with 1 vol. of N₂ gas in presence of catalyst (finely divided Fe at 450-500°C) and a basic gas ammonia is produced.

(c) Reduction of Fe₂O₃ (iron oxide) on heating to metal iron.

Question 9.
Using a burning candle and a jar of hydrogen – how would you prove experimentally that (a) Hydrogen is a combustible gas (b) Hydrogen does not support combustion.
Answer:

(a) Hydrogen gas is combustible and bums at the mouth of the gas jar. When a burning candle is brought near the mouth of hydrogen in gas jar.

(b) Hydrogen extinguishes the burning candle when pushed inside the jar. This shows that hydrogen does not support combustion.

Question 10.
State a reason why, when hydrogen is passed over heated copper oxide, the resultant product formed, differs in colour from the original reactant.
Answer:

H₂ removes oxygen from CuO and reduces it to Cu metal (reddish brown in colour).

Question 11.
With reference to the uses of hydrogen, give reasons for the following :

(a) Hydrogen is not used in air balloons
(b) A mixture of hydrogen & oxygen on burning, find application in welding & cutting metals
(c) Reaction of hydrogen with nitrogen under specific conditions finds industrial utility.

Answer:

(a) Hydrogen gas in ‘highly inflamable’ i.e. catches fire. Hence generally it is not used in air balloons.
(b) Hydrogen and oxygen mixture on burning produces a high temperature upto 2800°C which is used for welding and cutting of metals.
(c) One vol. of N₂ and 3 vol. of H₂ in presence of a catalyst (finely divided iron) at 450-500°C and at 200-900 mm pressure forms basic compound ammonia [NH₃] which finds applications in fertilizers and nitric acid [HNO₃] and explosives.

Question 12.
Give a test to differentiate between two gas jars – one containing pure hydrogen and the other hydrogen-air mixture.
Answer:
When a burning splinter is brought near the gas jar containing, pure H2 bums with pale blue flame quietly.
H₂ + Oxygen mixture bums with explosion.

Question 13.
With reference to oxidation & reduction reaction – complete the statement given by filling in the blanks with only the words (a) Addition (b) Removal.
‘Oxidation is a chemical reaction involving ____ of oxygen to a substance or ____ of hydrogen from a substance. Reduction on the otherhand involves ____ of hydrogen to a substance or ____ of oxygen from a substance.
Answer:
‘Oxidation is a chemical reaction involving – addition of oxygen to a substance or removal of hydrogen from a substance. Reduction on the otherhand involves addition of hydrogen to a substance or removal of oxygen from a substance.

Question 14.
With reference to the equation : Cl₂ + H₂S → 2HCl + S pertaining to a redox reaction – select the correct answer in each case –

(a) Chlorine is oxidised/redcued to HCl.
(b) Hydrogen sulphide is oxidised/redcued to sulphur since the reaction involves addition/removal of hydrogen.
(c) Chlorine acts as an oxidising/reducing agent.

Answer:

OBJECTIVE TYPE QUESTIONS

Q.1. Give balanced equations for the following conversions :

Question 1.
Zinc to sodium zincate – using an alkali.
Answer:
Zinc to sodium zincate.

Question 2.
Acidified water to hydrogen – by electrolysis.
Answer:

Question 3.
Water gas to hydrogen – industrially.
Answer:

CO₂ is removed by dissolving the mixture obtained in water under pressure
By passing the mixture through water or KOH [Caustic Potash Solution]
2KOH + CO₂ → K₂CO₃ + H₂0
Residual gas left is HYDROGEN.

Question 4.
Iron [III] oxide to iron – using hydrogen.
Answer:
Fe₂O₃ is reduced by hydrogen

Question 5.
Nitrogen to a basic gas – using hydrogen.
Answer:
Nitrogen to basic gas [NH₃] – using H₂

Q.2. Give reasons for the following :

Question 1.
Copper does not displace hydrogen from dilute hydrochloric acid, but zinc does.
Answer:
Copper lies below [H] in activity series of metals and cannot displace hydrogen from acid.
Zn lies above [H] in reactivity series of metals and being more reactive can displace hydrogen from dil. acids.

Question 2.
In the preparation of hydrogen by electrolysis of water – the distilled water used is acidified.
Answer:
Pure or distilled water is bad conductor of electricity and does not form ions. To increase the number of H⁺ ions distilled water is acidified and made good conductor of electricity.

Question 3.
In the laboratory preparation of hydrogen from zinc and dilute hydrochloric acid – the zinc used granulated zinc.
Answer:
Granulated zinc contains traces of impurities which act as catalyst and increase the rate of production of hydrogen.

Question 4.
In Bosch process – the final gaseous products are passed through caustic potash [KOH] soln.
Answer:
In Bosch process, final products are passed through caustic potash solution to separate hydrogen from the mixture. CO₂ dissolves in KOH leaving behind hydrogen.

Question 5.
The reaction of chlorine with hydrogen sulphide is deemed a redox reaction.
Answer:
Reaction of Cl₂ with H₂S is redox reaction as Cl₂ gets reduced to HCl and H₂S is oxidised simultaneously in the reaction. Hence it is redox reaction.

Q.3. Select the correct answer from A, B, C, D or E for each statement given below :
A: Nickel
B: Sodium
C: Iron
D: Iron [III] oxide
E: Magnesium oxide

Question 1.
A metal which reacts with water to give a metallic hydroxide & liberate hydrogen.
Answer:
B : Sodium

Question 2.
The metallic compound used as a catalyst in Bosch process.
Answer:
D : Iron [III] oxide

Question 3.
The metal used as a catalyst in hydrogenation of oils.
Answer:
A : Nickel

Question 4.
The metal which reacts with steam liberating hydrogen & the reaction is reversible.
Answer:
C : Iron

Question 5.
The metallic compound formed when a metal above aluminium in the activity series reacts with steam.
Answer:
E : Magnesium oxide

Q.4. Select the correct answer from the choice in bracket to complete each sentence.

Question 1.
The acid ___ [dil.H₂SO₄, dil. HNO₃, dil. HCl] is not Used in the laboratory preparation of hydrogen, using zinc and an acid.
Answer:
The acid dil. HNO₃ is not used in the laboratory preparation of hydrogen, using zinc and an acid.

Question 2.
In Bosch process the catalytic reduction of steam to hydrogen is carried out by ___ [CO₂, CO, C].
Answer:
In Bosch process the catalytic reduction of steam to hydrogen is carried out by CO [carbon monoxide].

Question 3.
A foul smelling gas formed when hydrogen reacts with a molten non-metal, is ___ [hydrogen chloride, hydrogen sulphide, ammonia].
Answer:
A foul smelling gas formed when hydrogen reacts with a molten non-metal, is hydrogen sulphide [H₂S].

Question 4.
The product formed on combustion of hydrogen in air is ___ [water gas, water, producer gas].
Answer:
The product formed on combustion of hydrogen in air is water.

Question 5.
The gas which has now replaced hydrogen in air balloons is ___ [argon, helium, neon].
Answer:
The gas which has now replaced hydrogen in air balloons is helium.

Q.5. Match the statements in List I with the appropriate answer in List II.

Answer:

New Simplified Chemistry Class 8 ICSE Solutions – Chemical Reactions

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

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EXERCISE

Question 1.
State what is a chemical reaction. A chemical reaction is often accompanied by external indications or characteristics which include – (a) Colour change (b) Effervescene or gas evolved (c) Evolution or absorption of heat (d) Formation of a precipitate. With reference to each of the above indications, state the external indication seen during – (i) Addition of dilute acid to an active metal (ii) Addition of dilute hydrochloric acid to silver nitrate (iii) Addition of water to quicklime (iv) Thermal decomposition of mercury [II] oxide.
Answer:
Chemical reaction : “Is a chemical change in which matter changes into a new substance or substances.”

1. Addition of dil. acid to an active metal : Gas is evolved, test tube or flask becomes hot (heat is produced).
2. Addition of dil. hydrochloric acid to silver nitrate : A white coloured precipitate of AgCl is seen.
3. Addition of water to quick lime : Hissing sound accompanied by a lot of heat (boiling).
4. Thermal decomposition of mercury [II] oxides : Red colour of Hg[II]0 changes to silvery (Hg metal).

Question 2.
State why a direct combination reaction is called a – ‘synthesis reaction’.
Answer:
When two or more substances [element with element or element with compound or compound with another compound] combine to form a new compound with new properties. Hence direct combination is called ‘synthesis reaction’.
Example : Hydrogen (a gas) + Oxygen (a gas) combines to form water (liquid).
2H₂ + O₂ → 2H₂0 H₂

Question 3.
Differentiate between –

(a) Direct combination reaction & a decomposition reaction
(b) Displacement reaction & a neutralization reaction.

Answer:
(a) Direct combination : “Is a reaction in which two elements or compound combine to give one new compound.”
C + O₂ → CO₂

• Decomposition reaction : “A chemical compound (breaks up) decomposes into two or more simpler substances.” Copper carbonate → Copper oxide + carbon dioxide
  CUCO₃ → CuO + CO₂
  

(b) Displacement reaction : “A chemical reaction in which an element displaces the element from a solution of its compound.”

In a activitiy series of metals, an element placed higher displaces the element placed below it.

Here Zn is placed above Cu in activity series of metal and is more reactive than copper has displaced Cu from copper sulphate.

• Neutralization reaction : “A reaction between an acid and a base to form salt and water is called neutralization reaction.”
  

Question 4.
Classify the following reactions into – (a) Direct combination (b) Decomposition (c) Displacement (d) Double decomposition – The reactions are – (i) Zinc hydroxide on heating gives zinc oxide & water (ii) Zinc reacts with copper [II] sulphate to give zinc sulphate & copper (iii) Zinc sulphate reacts with ammonium hydroxide to give ammonium sulphate & zinc hydroxide (iv) Molten zinc at high temperatures, burns in air to give zinc oxide.
Answer:

1. Zinc hydroxide a single compound decomposes into two simpler components zinc oxide and water, hence it is decomposition reaction.
2. Zinc reacts with copper [II] sulphate to give zinc sulphate and copper is displacement reaction. Zinc being more reactive than copper displaced copper from copper sulphate.
3. Is double decomposition as exchange of ions takes place.
   

Question 5.
Give balanced equations for –

1. A direct combination reaction involving two elements, one of which is a non-metal
2. A thermal decomposition reaction involving heat on limestone [calcium carbonate]
3. An electrolytic decomposition reaction involving a neutral liquid
4. A displacement reaction involving a metal above hydrogen in the activity series with copper [II] sulphate solution
5. A double decomposition neutralization reaction involving an acid & a base
6. A white precipitate obtained during a double decomposition reaction involving a silver salt with a sodium salt.

Answer:

1. Balanced chemical equation of : A combination reaction between calcium and oxygen (non-metal) to form calcium oxide.
   2Ca + O₂ → 2CaO
2. Thermal decomposition of limestone :
   
   
3. Electrolytic decomposition of neutral liquid [water]
   
4. Displacement reaction
   
   [more reactive displaces less reactive Cu]
5. Neutralization of acid with base to form salt and water.
   
6. Double decomposition reaction
   

Question 6.
State what is meant by ‘reactivity series of metals’. With reference to – (a) Water (b) Acids explain with suitable examples how the reactivity of the metals could be differentiated.
Answer:
Activity series of metals : “Is a series of arrangement of metals in decreasing order of their reactivity.”
i.e. metals at top are most reactive and least reactive metals are at the bottom of the series. Metal above is more reactive than the lower metal. In other words K is more reactive than all the metals below it and Na is more reactive than all the metals below it.
(a) Action of metals with water : K, Na, Ca react with cold water.
K : Darts on water surface and react violently.
Na : Revolves on the water surface and bums.
Ca : Sinks in water, react less violently.
Hence, K > Na > Ca calcium is less reactive than K and Na.
Mg and Al react with boiling water/steam.
Hence, Mg and Al are less reactive than K, Na and Ca. Zn, Fe, Pb also react with steam and reaction stops soon. Fe when hot reacts with steam
This shows that Mg > Al > Zn > Fe > Pb.
Cu, Hg, Ag, Pt, Au do not react with steam or even when hot are less reactive.
(b) Action of metals with acids : As reactivity decreases from top to bottom in metal activity series.
K and Na react with dil. HC1 and dil. H₂SO₄ explosively to produce H₂↑
2Na + 2HCl → 2NaCl + H₂
Ca, Mg, Al, Zn and iron react less vigorously with decreasing vigour with dil. H₂SO₄ or dil. HC1 to produce H₂↑
Ca + H₂SO → CaSO₄ + H₂
Metals below hydrogen do not react with dil. acid and do not displace H₂ from it.

Question 7.
A chemical reaction may be ‘reversible’ in nature. State the meaning of the term in italics. Give a reason why a catalyst is used in certain chemical reactions. Give a r balanced equation for the following – (a) A reversible catalytic reaction involving –

1. nitrogen as one of the reactants
2. sulphur dioxide as one of the reactants.

Answer:
Reversible reaction : “A chemical reaction is said to be reversible in nature if “products formed react together – to form actual reactants depending on the condition of the reaction.”

A catalyst is used to make the reaction fast or slow down it. When KClO₃ is heated, oxygen is produced but reaction is very slow. If we add MnO₂ to KClO₃ and heat the rate of production of oxygen becomes faster.
Balanced chemical equations for reversible reactions involving,

(a) Nitrogen as one of the reactants

(b) SO₂ as one of the reactants.

Question 8.
State which type of chemical reactions proceed with – (a) Evolution of heat energy (b) Absorption of heat energy. State in each of the following reactions whether heat is evolved or absorbed – (i) water is added to quicklime (ii) two neutral gases on passage through an electric arc give nitric oxide (iii) two neutral gases combine to give – a basic gas.
Answer:
(a) Exothermic reactions.
(b) Endothermic reactions.

1. When water is added to quicklime heat is evolved.
2. Nitrogen and oxygen.
3. Nitrogen gas and hydrogen gas give NH₃ (ammonia a basic gas).

Question 9.
Certain thermal decomposition reactions, result in formation of oxides. Give balanced equations for the thermal decomposition of the following, which result in formation of a metallic oxide

(a) Limestone

(b) Lead carbonate

(c) Calcium nitrate

(d) Calcium hydroxide.

Answer:

(a) Limestone CaCO₃ decomposes to CaO and CO₂
(b) Lead carbonate PbCO₃
(c) Calcium nitrate Ca[NO₃]₂
(d) Calcium hydroxide

Question 10.
State the meaning of the term ‘oxide’. Give a balanced equation for formation of the following oxides –

(a) Sulphur dioxide from a non-metal
(b) Zinc oxide from a metal
(c) Lead oxide from a mixed Oxide.

Answer:
Oxide is product obtained on combining with oxygen.
i. e. combination with oxygen.
OR
Binary compounds of a metallic or non-metallic element with oxygen.

Question 11.
Give two examples each of the following oxides – (a) Acidic oxides (b) Basic oxides (c) Amphoteric oxides (d) Neutral oxides. State which of the following oxides i.e. (a) to (d) (i) React with water to give a base (ii) React with a base to give salt & water (iii) React with acids & bases to give salt & water.
Answer:
(a) Acidic oxides : Non-metallic oxides are acidic oxides.

1. SO₂
2. CO₂
3. NO₂ are acidic oxides.

(b) Basic oxides : Metallic oxides are basic oxides.

1. Na20
2. K20
3. CaO are basic oxides.

(c) Amphoteric oxides : Oxides of metals like Zn, Pb, Al are amphoteric oxides.

1. ZnO
2. PbO
3. Al₂O₃ are amphoteric oxides.

(d) Neutral oxides : Oxides like NO,CO,N₂0 are neutral oxides.

1. Basic oxides react with water to give bases.
2. Acidic oxide reacts with base to give salt and water.
3. Amphoteric oxide reacts with acids and bases to give salt and water.

Question 12.
Give one example each of –

(a) A peroxide
(b) A mixed oxide
(c) A dioxide.

Answer:
Examples of :

(a) A peroxide — Na₂O₂ (Sodium peroxide)
(b) A mixed oxide — Pb₃0₄
(c) A dioxide – PbO₂

OBJECTIVE TYPE QUESTIONS

Q.1. Select the correct answer from A, B, C, D and E for each statement given below :
A: Iron
B: Carbonic acid
C: Hydrogen
D: Oxygen
E: Carbon monoxide

Question 1.
The product formed during direct combination reaction of carbon dioxide & water.
Answer:
B: Carbonic acid

Question 2.
The neutral gas obtained on thermal decomposition of potassium nitrate.
Answer:
D: Oxygen

Question 3.
The displaced product of the displacement reaction of sodium with cold water.
Answer:
C: Hydrogen

Question 4.
The catalyst used in the catalystic reaction involving the reactants nitrogen & hydrogen.
Answer:
A: Iron

Question 5.
A neutral oxide which does not react with an acid or a base to give salt & water.
Answer:
E: Carbon monoxide

Q.2. Complete the statements by filling in the blank with the correct word/s :

Question 1.
Direct combination reaction of phosphorus pentoxide with water gives ___ [H₃PO₃/H3PO₄].
Answer:
Direct combination reaction of phosphorus pentoxide with water gives H₃PO₄.

Question 2.
Decomposition of silver salts in the presence of sunlight is an example of ___ [double decomposition/photochemial decomposition].
Answer:
Decomposition of silver salts in the presence of sunlight is an example of  photochemial decomposition.

Question 3.
The element molybdenum used in the reaction of nitrogen with hydrogen at elevated temperatures is an example of a ___ [promoter/catalyst].
Answer:
The element molybdenum used in the reaction of nitrogen with hydrogen at elevated temperatures is an example of a promoter.

Question 4.
The reaction of coke with steam to give water gas is an example of an ___ [exothermic/endothermic] reaction.
Answer:
The reaction of coke with steam to give water gas is an example of an endothermic reaction.

Question 5.
The metal which reacts with steam and the reaction is reversible is ___ [calcium/iron].
Answer:
The metal which reacts with steam and the reaction is reversible is iron.

Q.3. Give a balanced equation for each of the following types of reactions :

Question 1.
A thermal decomposition reaction in which a compound decomposes to give two new compounds.
Answer:

Question 2.
A reaction of direct combination i.e. synthesis in which twp gases combine to give another gas – which turns lime wafer milky.
Answer:
Synthesis when two gases combine to give a gas which turns lime water milky.

Question 3.
A thermal decomposition reaction in which a metallic nitrate decomposes to give – a basic oxide.
Answer:
Metallic nitrate is calcium nitrate on thermal decomposition gives CaO which is a basic oxide.

Question 4.
A catalytic, reversible, exothermic reaction.
Answer:
A catalytic, reversible, exothermic reaction.

Question 5.
A displacement reaction in which a metal above hydrogen in the reactivity series, displaces another metal from the solution of its compound.
Answer:

Q.4. Differentiate between the following :

Question 1.
Thermal decomposition & thermal dissociation.
Answer:
Thermal decomposition and thermal dissociation.
Decomposition of a compound on heating into two elements or element and compound or into two new compounds. It is irreversible reaction.
Thermal dissocation is the decomposition of a substance into two or more simpler substances on heating but reaction is reversible.

Question 2.
Neutralization reaction & a precipitation reaction.
Answer:
Formation of salt and water when an acid reacts with a base is called neutralisation.

• Precipitation : Formation of semi solid (insoluble) product in called precipitation.
  

Question 3.
Electrolytic decomposition & photochemical decomposition.
Answer:

• Electrolytic decomposition : “A decomposition reaction which is brought about by – passage of electric current.”
  
• Photochemical decomposition : “A decomposition reaction which takes place in presence of light.”
  e.g. decomposition of silver salts in presence of sun light.

Question 4.
A catalyst & a promoter.
Answer:

• Catalyst : “A substance which alters the rate of chemical reaction.”
  e.g. MnO₂, V₂O₅, Fe, Pt. etc.
• The positive catalyst : A catalyst which speeds up the reaction.
• Negative catalyst : A catalyst which reduces the rate of reaction, e.g. alcohol.
  Enzymes are biological catalysts present in human body and accelerate the biochemical reactions in the body.
• Promotors is a catalyst to catalyst, i.e. a substance which increases the activity of a catalyst.
  Molybdenum [MO] is added to the catalyst iron [Fe] to increase its efficiency.

Question 5.
An acidic oxide & a basic oxide.
Answer:

• Acidic oxide : Non-metal oxide is called acidic oxide i.e. SO₂, NO₂ when acidic oxide dissolves in water forms acid.
• Basic oxide : Metallic oxide is called basic oxide, e.g. CaO, Na₂O basic oxide dissolved in water is called alkali.

Q.5. Match the chemical reactions in List I with the appropriate answer in List II.

Answer: