Selina Class 8 ICSE Solutions

Selina Concise Chemistry Class 8 ICSE Solutions – Language of Chemistry

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Selina Concise Chemistry Class 8 ICSE Solutions – Language of Chemistry

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 5 Language of Chemistry. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 5 Language of Chemistry

Points to Remember:

  • The valency of an element is the number of electrons donated or accepted by its ‘atom’ during chemical combination.
  • There are some elements with more than one valency e.g., iron, copper, tin, lead.
  • Two or more different non-metals that collectively accept or donate one or more electrons and become negatively or positively charged in the process are called radicals.
  • A chemical reaction involves the transformation of original substance into an altogether new substance(s).
  • A chemical reaction can be represented with the help of the symbols or the formulae of the elements and the compounds taking part in that reaction. This gives a chemical equation.
  • Certain necessary conditions for a chemical reaction to happen are — close contact, solution form, heat, light and catalyst.
  • Characteristics of chemical reactions are — change of colour, evolution of a gas, formation of a precipitate, change of state, change of smell and evolution/absorption of heat.
  • A complete chemical equation symbolically represents the reactants, products and their physical states.
  • The substances that react with each other are called reactants and they are represented on the left hand side of the equation. The substances that are formed as a result of the reaction are called products. They are represented on the right hand side of the equation.
  • A chemical equation needs to be balanced to make it follow the law of the conservation of mass.
  • The law of conservation of mass states that mass can be neither created nor destroyed, it can only be transformed from one form to another.
  • A chemical equation gives both qualitative and quantitative information about the reactants and products.

ACTIVITY 1
Write the names and symbols of the first twenty elements that you have studied in class VI & VII.
Answer:
selina-concise-chemistry-class-8-icse-solutions-language-of-chemistry-1

ACTIVITY 2
Write the molecular formulae of:

  1. Copper oxide
  2. Iron (III) chloride
  3. Sodium hydroxide
  4. Iron (II) sulphide
  5. Lead (II) oxide
  6. Hydrogen nitrate (nitric acid)
  7. Hydrogen sulphate (sulphuric acid)
  8. Calcium hydroxide
  9. Magnesium carbonate
  10. Ammonium carbonate

Answer:

  1. Copper oxide – CuO
  2. Iron (III) chloride – FeCl3
  3. Sodium hydroxide – NaOH
  4. Iron (II) sulphide – FeS
  5. Lead (II) oxide – PbO
  6. Hydrogen nitrate (nitric acid) – HNO3
  7. Hydrogen sulphate (sulphuric acid) – H2SO4
  8. Calcium hydroxide – Ca(OH)2
  9. Magnesium carbonate – MgCO3
  10. Ammonium carbonate – (NH4)2CO3

ACTIVITY 3
Write the molecular formula for each of the following compounds:

  1. Sulphur trioxide
  2. Iron (II) sulphide and
  3. Ammonia

Find the number and names of elements present in them and calculate their molecular masses.
Answer:
1. Sulphur trioxide

  1. A molecule of sulphur trioxide is represented by the formula SO3.
  2. The elements present in it are sulphur dioxide and oxygen.
  3. One molecule of sulphur trioxide has one atom of sulphur and three atoms of oxygen.
  4. Molecular mass of sulphur trioxide (SO3)
    = 32 + 3 x 16
    = 32 + 48 = 80 amu.

2. Iron (II) sulphide

  1. A molecule of iron (II) sulphide is represented by the formula FeS.
  2. The elements present in it are iron and sulphur.
  3. One molecule of iron (II) sulphide has one atom of iron and one atom of sulphur.
  4. Molecular mass of iron (II) sulphide (FeS)
    = 55.5 + 32
    = 87.5 amu.

3. Ammonia

  1. A molecule of ammonia is represented by the formula NH3.
  2. The elements present in it are nitrogen and hydrogen.
  3. One molecule of ammonia has one atom of nitrogen and three atoms of hydrogen.
  4. Molecular mass of ammonia (NH3)
    = 14 + 3 x 1
    = 14 + 3
    = 17 amu.

Exercise

Question 1.
Define:
(a) Radical
(b) Valency
(c) Molecular formula
Answer:
(a) Radical: A radical is an atom of an element or a group of atoms of different elements that behaves as a single unit with a positive or negative charge on it.
(b) Valency: It is the number of electrons donated or accepted by the valence shell of an atom during chemical combination.
(c) Molecular formula: It is a symbolic representation of a molecule. It shows the number of atoms of each element present in it. These atoms combine in whole number to form the molecule.

Question 2.
Give the symbols and valencies of following radicals:
(a) Hydroxide (b) Chloride
(c) Carbonate (d) ammonium
(e) Nitrate
Answer:
selina-concise-chemistry-class-8-icse-solutions-language-of-chemistry-2

Question 3.
Write the molecular formula for the oxide and sulphide of following elements.
(a) Sodium (b) Calcium
(c) Hydrogen
Answer:
(a) Sodium oxide Na2O
Sodium sulphide Na2S
(b) Calcium oxide CaO
Calcium sulphide CaS
(c) Hydrogen oxide H2O
Hydrogen sulphide H2S

Question 4.
Write the molecular formulae for the following compounds and name the elements present.
(a) Baking soda (b) Common salt
(c) Sulphuric acid (d) Nitric acid
Answer:
(a) Baking soda — NaHCO3
Elements present in Baking soda are sodium, hydrogen, oxygen and carbon.
(b) Common salt — NaCl
Element present are: Sodium and chlorine.
(c) Sulphuric acid — H2SO4
Element present are: Hydrogen, sulphur and oxygen.
(d) Nitric acid — HNO3
Elements present are: Hydrogen, nitrogen and oxygen.

Question 5.
The valency of aluminium is 3. Write the valency of other radicals present in the following compounds.
(a) Aluminium chloride
(b) Aluminium oxide
(c) Aluminium nitride
(d) Aluminium sulphate
Answer:
(a) Aluminium chloride — (AlCl3) here valency of Al is 3.
Other radical – Chloride (Cl–)
Valency of chloride = 1
(b) Aluminium oxide — (Al2O3)
Here valency of Al is 3
Other radical present = oxide (O2-)
Valency of O2- = 2
(c) Aluminium nitride — (Al N)
Here valency of aluminium = 3
Another radical = Nitride (N3-)
Valency of nitride (N3-) = 3
(d) Aluminium sulphate — Al2(SO4)3
Here valency of aluminium is 3
Another radical = Sulphate (SO42-)
Valency of (SO42-) = 2

Question 6.
What is variable valency ? Give two examples of elements showing variable valency.
Answer:
Certain elements exhibit more than one valency, that means they show variable valency.
Ferrous is written as Iron (II) and Ferric is written as Iron (III).

MetalRadicalsValency
IronFerrous [Iron (II)]
Ferric [Iron (III)]		2
3
CopperCuprous [Copper (I)]
Cupric [Copper (II)]		1
2

Question 7.
(a) What is a chemical equation ?
(b) Why it is necessary to balance a chemical equation ?
(c) What are the limitations of a chemical equation ?
Answer:
(a) Chemical Equation— A chemical equation is the symbolic representation of a chemical reaction using the symbols and the formulae of the substances involved in the reaction.
(b) A chemical equation needs to be balanced so as to make the number of the atoms of the reactants equal to the number of the atoms of the products.
(c)

  1. It does not inform about the physical states of the reactants and the product i.e. whether they are solids, liquids and gases.
  2. It does not inform about the concentration of reactants and products.
  3. It does not inform about the time taken for the completion of the reaction.
  4. It does not inform about the rate at which a reaction proceeds.
  5. It does not inform about the heat changes during the reaction i. e. whether the heat is given out or absorbed.
  6. It does not inform about the conditions such as temperature, pressure, catalyst etc. which affect the reaction.
  7. It does not inform about the nature of the reaction i.e. whether it is reversible or irreversible.

Question 8.
What are the ways by which a chemical equation can be made more informative ?
Answer:
A chemical equation can give more informations in the following ways:

  1. The physical state of the reactants and products can be indicated by putting (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous state.
  2. Evolution or absorption of heat during the reaction can be denoted by adding or subtracting a heat term on the product side.
  3. Temperature, pressure and catalyst can be indicated above the arrow (→ or =) separating the reactants and products.
  4. Concentration of reactants and products are indicated by adding word (dil) for dilute and (cone) for concentrated before their formulae.
  5. By the sign → or \(\rightleftharpoons \) information about irreversible and reversible reactions can be obtained.

Question 9.
State the law of conservation of mass.
Answer:
Law of conservation of mass: It states that mass can neither be created nor destroyed in a chemical reaction. During any change (physical or chemical), matter is neither created nor destroyed. However it may change from one form to another.
selina-concise-chemistry-class-8-icse-solutions-language-of-chemistry-3
Experimental Verification of Law of Conservation of Mass

Requirements: H-shaped tube called Landolt’s tube, Sodium chloride solution, silver nitrate solution, etc.
Procedure: A specially designed H-shaped tube is taken. Sodium chloride solution is taken in one limb of the tube and silver nitrate solution in the other limb as shown in figure.
Both the limbs are now sealed and weighed. Now the tubes is averted so that the solutions can mix up together and react chemically. The reaction takes place and a white precipitate of silver chloride is obtained.
selina-concise-chemistry-class-8-icse-solutions-language-of-chemistry-4
The tube is weighed again. The mass of the tube is found to be exactly the same as the mass obtained before inverting the tube.
Thus, this experiment clearly verifies the law of conservation of mass.

Question 10.
Differentiate between:
(a) Reactants and products
(b) A balanced and an unbalanced chemical equation
Answer:
(a) Reactants and products

Reactants

  1. The substances that react with one another are called reactants.
  2. Reactants are written on the left hand side of equation.

Products

  1. The new substances formed are called products.
  2. Products are written on the right hand side of equation.

(b) A balanced and an unbalanced chemical equation

Balanced chemical

  1. A balanced chemical reaction is the one in which the number of atoms of each element on the reactant side is equal to the number of atoms of that element on the product side.
  2. Ex- H2 + Cl2 → HCl

Unbalanced chemical

  1. Number of elements on reactant side are not equal to the number of elements on product side.
  2. Ex- H2 + Cl2 → 2HCl

Question 11.
Balance the following equations:
selina-concise-chemistry-class-8-icse-solutions-language-of-chemistry-5
Answer:
selina-concise-chemistry-class-8-icse-solutions-language-of-chemistry-6

Question 12.
12. Write balanced chemical equations for the following word equations:
(a) Iron + Chlorine → Iron (III) chloride
(b) Magnesium + dil sulphuric acid → Magnesium sulphate + water
(c) Magnesium + oxygen → Magnesium oxide
(d) Calcium oxide + water → Calcium hydroxide
(e) Sodium + chlorine → Sodium chloride
Answer:
(a) Iron + Chlorine → Iron (III) chloride
4Fe + 3Cl2 → 2F2Cl3
(b) Magnesium + dil sulphuric acid → Magnesium sulphate + water
2Mg + 2H2SO4 → 2MgSO4 + 2H2
(c) Magnesium + oxygen → Magnesium oxide
2Mg + O2 → 2MgO
(d) Calcium oxide + water → Calcium hydroxide
CaO + H2O → Ca(OH)2
(e) Sodium + chlorine → Sodium chloride
2Na + Cl2 → 2NaCl

Question 13.
What information do you get from the following chemical equation:
Zn(s) + 2HCl (dil) → ZnCl2 (aq) + H2(g)
Answer:
This gives zinc chloride and hydrogen. The word equation is:
Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
Formulae for the products are ZnCl2 and H2

Selina Concise Chemistry Class 8 ICSE Solutions – Elements, Compounds and Mixtures

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Selina Concise Chemistry Class 8 ICSE Solutions – Elements, Compounds and Mixtures

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 3 Elements, Compounds and Mixtures. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 3 Elements, Compounds and Mixtures

Exercise 3(A)

Question 1.
Define: (a) Elements (b) Compounds
Answer:
(a) Elements: Element is a substance which cannot be broken further into simpler substances and has a definite set of properties. Elements are made up of only one kind of atoms.
(b) Compounds: Compounds are pure substances composed of two or more elements in definite proportion by mass and has properties, entirely different from those of its constituents elements.
Compound, are made up of different types of atoms combined chemically.

Question 2.
Give two examples for each of the following:
(a) Metals (b) Non-metals
(c) Metalloids (d) Inert gases
Answer:
(a) Metals: Iron, silver, gold.
(b) Non-metals: Carbon, sulphur, oxygen.
(c) Metalloids: Antimony, silicon, boron.
(d) Inert gases: Helium, argon, neon.

Question 3.
Differentiate between:
(a) Pure and impure substances
(b) Homogenous and heterogenous substances
Answer:
(a) Pure substances —

  1. Pure substances have definite composition and definite physical and chemical properties.
  2. They are all homogeneous i.e. their composition is uniform throughout the bulk.
  3. Examples: Elements and compounds.

Impure substances —

  1. Impure substances are made up of two or more pure substances mixed together in any proportion.
  2. They may be homogeneous or hetergeneous i.e. their composition is not uniform throughout the bulk.
  3. They are all mixtures.
    Examples: air, sea water, petroleum, a solution of sugar in water are all impure substances.

(b) Homogeneous mixture — is a mixture where the components that make up the mixture are uniformly distributed throughout the mixture.
Example — air, sugar water, rain water.
Heterogeneous mixture — is a mixture, where the components of the mixture are not uniform or have localized regios with different properties.
Example—Cereal in milk, vegetable soup.

Question 4.
Write the chemical name of the following and also give their molecular formulae:
(a) Baking soda (b) Vinegar
(c) Marble (d) Sand
Answer:
(a) Sodium bicarbonate (Baking soda) — NaHCO3
(b) Acetic acid (Vinegar) — CH3COOH
(c) Calcium carbonate (Marble) — CaCO3
(d) Silicon dioxide (Sand) — SiO2

Question 5.
Name:
(a) a soft metal
(b) a metal which is brittle
(c) a non-metal which is lustrous
(d) a liquid metal
(e) a metal which is a poor conductor of electricity.
(f) a non-metal which is a good conductor of electricity.
(g) a liquid non-metal
(h) the hardest naturally occurring substance
(i) an inert gas
Answer:
(a) Gold
(b) Zinc
(c) Iodine
(d) Mercury
(e) Tungsten
(f) Graphite
(g) Bromine
(h) Diamond
(i) Neon, helium

Question 6.
How is sodium chloride different from its constituent elements ?
Answer:
The properties of sodium chloride are completely different from those of sodium and chlorine. Sodium is a soft, highly reactive metal. Chlorine is a poisonous non-metallic gas while sodium chloride is a very useful non poisonous compound which is added to our food to get minerals and also to add taste to it.

Question 7.
Why is iron sulphide a compound ?
Answer:
Iron sulphide is a compound which can be broken into the elements iron and sulphur they both have different properties. The properties of compound are entirely different from there of its constituents elements.

Exercise 3(B)

Question 1.
Classify the following substances into compounds and mixtures:
Answer:
Carbon dioxide, air, water, milk, common, salt, blood, fruit juice, iron sulphide.
Carbon dioxide — (Compound)
air — (Mixture)
water — (Compound)
milk — (Mixture)
common salt — (Compound)
blood — (Mixture)
fruit juice — (Mixture)
iron sulphide — (Compound)

Question 2.
Give one example for each of the following types of mixtures
(a) solid-solid homogenous mixture
(b) solid-liquid heterogenous mixture
(c) misicible liquids
(d) liquid-gas homogenous mixture
Answer:
(a) Solid-solid homogenous mixture — Alloys of metals e.g. brass, bronze stainless steel etc.
(b) Solid-liquid heterogenous mixture — Sand and water, mud and water, sugar and oil.
(c) Misicible liquids — water and ethanol.
(d) Liquid-gas homogenous mixture — Air

Question 3.
Suggest a suitable technique to separate the constituents of the following mixtures. Also give the reason for selecting the particular method.
(a) Salt from sea water
(b) Ammonium chloride from sand
(c) Chalk powder from water
(d) Iron from sulphur
(e) Water and alcohol
(f) Sodium chloride and potassium nitrate
(g) Calcium carbonate and sodium chloride
Answer:

(a) The technique used to separate the salt from seawater is Evaporation.
Reason – Because this method is used to separate the components of the homogeneous solid-liquid mixture. In this method, sea water is collected in a shallow bed and allowed to evaporate in the sun. When all the water is evaporated, salt is left behind. By this method, we only get solid and liquid is evaporated in its vapour form.

(b) Technique used to separate Ammonium chloride from sand is sublimation.
Because this method is used for solid mixtures in which one of the components can sublime on heating. In this method, Ammonium chloride changes into vapours on heating and salt is left behind.

(c) Technique used to separate chalk powder from water is filtration.
Reason – Because this process is used to separate the components of a heterogeneous solid-liquid mixture in which solids are lights and insoluble in liquids. Substances used as filters are sand filter paper at C. These filters allows the liquid to pass through them, but not solids.

(d) Technique to separate iron from sulpher is magnetic separation.
Because, this method is used when one of the component of mixture is Iron. Iron gets attracted towards the magnet and hence get separated.

(e) Technique used to separate water and Alcohol is Fractional Distillation.
Because in this method, the vapours of water is left behind in the original vessel as the alcohol boils at lower temperature than water. Thus these two liquids can be separated.

(f) Technique used is Fractional-crystallisation.
Because: This method is used when solubility of solid components of mixture and different in the same solvent. Here, sodium chloride and potassium nitrate. Both are soluble in water but solubility of potassium nitrate is more.

(g) Technique used is Solvent Extraction Method: Because, by this method, salts get dissolve in water while calcium carbonate being insoluble in water settles down in the container. And hence get separated about.

Question 4.
(a) Define mixture.
(b) Why is it necessary to separate the constituents of a mixture.
(c) State four differences between compounds and mixtures.
Answer:
(a) “Mixtures can be defined as. a kind of matter which is formed by mixing two or more pure substances (elements and compounds) in any proportion, such that they do not undergo any chemical change and retain their individual properties. Therefore they are impure substances.

(b) Because: The mixtures contain unwanted substances which may be harmful and may degrade the properties of mixtures. So we, need to separated them and extract useful substances.
This is necessary because
(i) It removes unwanted and harmful substances
(ii) to obtain pure and useful substances them.
Example: Sea water is rich in common salt which is an important ingredient of our food to add taste and nutrients. But sea water, cannot be directly used to get the salt.
Hence, it is necessary to separate both.

(c) Compound

  1. A compound is formed from its constituent elements as a result of chemical reaction.
  2. A compound is always homogeneous in nature.
  3. In a compound the elements are present in a fixed ratio by weight.
  4. The components of a compound can’t be separated by physical methods but can be separated by chemical methods only.
  5. The properties of a compound are different from those of its elements.
  6. The formation of a compound from its elements is accompanied by energy changes.

Mixture

  1. A mixture is obtained form its (elements, compounds) components as a result of physical change.
  2. The mixtures can be homogeneous or heterogeneous.
  3. In a mixture the components can be present in any ratio.
  4. The components of a mixture can be separated by physical methods only.
  5. The properties of a mixture lie between those of-its components.
  6. The formation of a mixture from its constituents is not accompanied by energy changes.

Question 5.
(a) What is chromatography ? For which type of mixture is it used ?
(b) What are the advantages of chromatography.
Answer:
(a) This is one of the latest techniques to separate the coloured components of a mixture when all the components are very similar in their properties. Example: Components of ink are separated by this method. Ink is a mixture of different dyes, which are separated by chromatography because some of the dyes are less soluble and some are more soluble in a solvent.

(b)

  1. A very small quantity of the substance can be separated.
  2. Components with very similar physical and chemical properties can be separated.
  3. It identifies the different constitutes of a mixture.
  4. It also helps in quantitive estimation of components of a mixture.

6. Choose the most appropriate answer from the options given below:

(a) a mixture of sand and ammonium chloride can be separated by

  1. filtration
  2. distillation
  3. sublimation
  4. crystallisation

(b) A pair of metalloids are

  1. Na and Mg
  2. B and Si
  3. C and P
  4. HeandAr

(c) Which of the following property is not shown by compounds?

  1. They are heterogeneous.
  2. They are homogeneous.
  3. They have definite molecular formulae.
  4. They have fixed melting and boiling points.

(d) A solvent of Iodine is

  1. Water
  2. Kerosene oil
  3. Alcohol
  4. Petrol

(e) Which of the gas is highly soluble in water ?

  1. Ammonia
  2. Nitrogen
  3. Carbon monoxide
  4. Oxygen

Selina Concise Chemistry Class 8 ICSE Solutions – Matter

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Selina Concise Chemistry Class 8 ICSE Solutions – Matter

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 1 Matter. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 1 Matter

Exercise

Question 1.
Define:
(a) matter
(b) intermolecular force of attraction.
Answer:
(a) Matter is anything which has mass, occupies space and can be percieved by our senses.
Example: Air, Book.
(b) The molecules of matter are always in motion and attract each other with a force called intermolecular force of attraction due to which they are held together.

Question 2.
What are the three states of matter ? Define each of them with two examples.
Answer:
The three states of matter are:
solids, liquids and gases

  • Solids — A solid has a definite shape and definite volume.
    Example – wood, stone, iron, ice etc.
  • Liquid — A liquid has a definite volume but not definite shape.
    Example — water, juice, milk, oil, etc.
  • Gases — A gas neither has definite shape nor a definite volume.
    Example – air, hydrogen, oxygen, watervapour etc.

Question 3.
Define interconversion of states of matter. What are the two factors responsible for the change of states of matter?
Answer:
The process by which matter changes from one state to another and back to original state, without any change in its chemical composition is called interconversion state of matter.
Two factors responsible for change of state of matter are: change in
(i) Temperature (ii) Pressure

Question 4.
State the main postulates of kinetic theory of matter.
Answer:
The main postulates of the theory are:

  1. Matter is composed of very small particles called atoms and molecules.
  2. The constituent particles of a kind of matter are identical in all respects.
  3. These particles have space or gaps between them which is known as interparticular or intermolecular space.
  4. There exists a force of attraction between the particles of matter which holds them together. This force of attraction is known as interparticular or intermolecular force of attraction.
  5. Particles of matter are always in a state of random motion and possess kinetic energy, which increases with increase in temperature and vice-versa.

Question 5.
What happens to water if
(a) it is kept in a deep freezer
(b) it is heated
Explain the phenomenon of change of state of water.
Answer:
(a) When water is kept in a deep freezer, it gets cooled and change into ice at 0°C ice.
selina-concise-chemistry-class-8-icse-solutions-matter-1
(b) Water on heating changes into steam at 100°C
selina-concise-chemistry-class-8-icse-solutions-matter-2
Phenomenon of change of state of water:
Water is a liquid under ordinary conditions but, when it is kept in a deep freezer, it changes into ice at 0°C and when ice is kept at room temperature again changes back into liquid water.
Similarly, water on heating change into steam at 100°C, which on cooling changes back into liquid water. But there is no change in the chemical composition of water. When its state changes from liquid to solid or liquid to gaseous state.
selina-concise-chemistry-class-8-icse-solutions-matter-3

Question 6.
(a) State the law of conversation of mass.
(b) What do you observe when, barium chloride solution is mixed with sodium sulphate solution ?
Answer:
(a) “Matter can neither be created nor be destroyed in a chemical reaction”. However, it may change from one form to another in the process.
It can also be stated as, “In a chemical reaction, the total mass of the reactants is equal to the total mass of the products”.

(b)
selina-concise-chemistry-class-8-icse-solutions-matter-4
We will observe that a white insoluble solid (precipitate) of barium sulphate is formed along with a solution of sodium chloride. Wait for ten minutes to complete the reaction and the solid formed to settle down.
Weigh the content again and note the reading.
We will observe that,
total mass of the apparatus + reactants = total mass of apparatus + products
Hence the law of conservation of mass is verified.

Question 7.
Give reasons:
(a) A gas can fill the whole vessel in which it is enclosed.
(b) Solids cannot be compressed.
(c) Liquids can flow.
(d) When magnesium is burnt in air, there is an increase in mass after the reaction.
Answer:
(a) Because, in gases, the molecules are free to move.
They are not stuck to each other and the intermolecular force of attraction is least in the gases. So the gas almost filled the whole vessel in which it is enclosed.

(b) In solids, particles are closely packed. There is a strong force of attraction and the intermolecular space is almost zero. Therefore the molecules are not free to move, which makes them hard and rigid. So solids can not be compressed.

(c) In liquids intermolecular force is weaker because the particles are not closely packed and hence there is large intermolecular space. So molecules in a liquids can move randomely and hence liquids can flow easily.

(d) When magnesium ribbon is burnt in air, a white solid, magnesium oxide is formed. The mass of magnesium oxide is
more than the mass of magnesium. This is because mass of oxygen used is not taken. If that is considered, the total mass of the reactants and the products is found to be almost equal.
selina-concise-chemistry-class-8-icse-solutions-matter-5

Question 8.
Fill in the blanks:

(a) The change of a solid into a liquid is called melting or fusion.
(b) The process in which a solid directly changes into a gas is called sublimation.
(c) The change of water vapour into water is called condensation.
(d) The temperature at which a liquid starts changing into its vapour state is evaporation or vaporisation.

Question 9.
Give two examples for each of the following:
(a) The substances which sublime.
(b) The substances which do not change their state on heating.
Answer:
(a) Camphor, iodine, naphthalene, ammonium chloride, dry ice (solid carbon dioxide), etc.
(b) Gases do not change their state on heating.
Example: O2.

Question 10.
Define:
(a) Diffusion.
(b) Brownian motion.
Answer:
(a) Diffusion: The intermixing of two or more substances due to the motion of their particles in order to get a uniform mixture is called ‘diffusion’.
(b) Brownian motion: The haphazard, random motion of suspended particles on the surface of a liquid or in air is called ‘Brownian motion’.

Question 11.
When sodium chloride is added to a definite volume of water and stirred well, a solution is formed, but there is no increase in the level of water. Why?
Answer:
This is because there is some space between the particles of water in which the salt particles get accomodated when dissolved.

Question 12.
What do you observe when a gas jar which appears empty is inverted over a gas jar containing Bromine vapours? Name the phenomenon.
Answer:
When a gas jar full of bromine vapours (reddish brown) is inverted over a gas jar containing air over it. It is observed that after sometime, the reddish brown vapours of bromine also spread out into the upper jar. This mixing is called diffusion. The rate of diffusion is the fastest in gases and the slowest in solids. It increases with an increase in temperature.

Question 13.
Why can a piece of chalk be broken easily into smaller pieces while a coal piece cannot be broken easily?
Answer:
The particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction is lesser in chalk, hence it could be broken easily into smaller pieces.
But the strength of inter-molecular force of attraction is very strong in coal, therefore it is not possible to break them into small pieces.

Selina Concise Biology Class 8 ICSE Solutions – Nervous System

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Selina Concise Biology Class 8 ICSE Solutions – Nervous System

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 7 Nervous System. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Biology Chapter 7 Nervous System

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) Medulla oblongata controls

  1. Smelling
  2. Beating of heart and respiratory movement
  3. Intelligence and will power
  4. Balancing the body

(b) Balance of body is controlled by:

  1. Spinal cord
  2. Cerebellum
  3. Cerebrum
  4. Medulla

(c) The smell of good food causes watering of your mouth. It is a

  1. Natural reflex
  2. Acquired relfex
  3. Inborn reflex
  4. Ordinary reflex

(d) The structural and functional unit of nervous system is a

  1. Axon
  2. Nephron
  3. Neuron
  4. Texon

Short Answer Questions:

Question 1.
Name the two types of coordination which take place in our body.
Answer:
(a) Nervous coordination: By nerves and brain
(b) Chemical coordination: By hormones

Question 2.
Your are driving your bicycle at a fast speed. Suddenly, a small boy comes in front of your cycle and, without wasting any time in thinking, you immediately apply the brakes and accident is avoided. What name is given to such an action?
Answer:
Reflex action (acquired).

Question 3.
Given below is the diagram of a neuron. Name the parts numbered 1-5.
Selina Concise Biology Class 8 ICSE Solutions – Nervous System 1
Answer:

  1. Dendrite
  2. Nucleus
  3. Cell Body (Nyton)
  4. Axon (Nerve fibre)
  5. Node of Ranvier

Question 4.
Write one word in the space provided to complete the second pair of the related words pertaining to nervous system.
Memory : cerebrum : : breathing :
Balance : cerebellum : : reasoning :
Answer:
Memory : cerebrum : : breathing: medulla oblongata
Balance : cerebellum : : reasoning : cerebrum

Question 5.
Differentiate between the following pair of terms:
(a) Stimulus and impulse
(b) Receptor and effector
(c) Motor nerve and sensory nerve
Answer:
(a) Stimulus: Any change in the environment that usually results in change in the activity of the body.
Impulse: A wave of electrical disturbance that runs through the nerves.

(b) Receptor: The nerve cell on receiving the stimulus sets up the waves of impulses towards the central nervous system.
Effector: Any muscle or gland on receiving the impulse from the brain (or the spinal cord), contracts or secretes.

(c) Motor nerve: It contains only motor neurons,
Example: Nerves going to the muscles of the eyeball.
Sensory nerve: It contains only sensoiy neurons.
Example: optic nerve of the eye.

Question 6.
(a) Name the three major divisions of the human nervous system.
(b) Name the three main parts of human brain.
Answer:
(a)

  1. The central nervous system (brain and spinal cord)
  2. The peripheral nervous system
  3. The autonomic nervous system

(b)

  1. Cerebrum
  2. Cerebellum
  3. Medulla oblongata

Question 7.
Give the function of each of the following:
(a) Olfactory nerve:
(b) Optic nerve:
(c) Facial nerve:
Answer:
(a) Olfactory nerve: The sense of smell is present in the epithelial layers of the nasal chambers. The sense of smell is carried to the brain by the olfactory nerve. They arise from the anterior ends of the olfactory lobes and are distributed to lining of nasal chambers.
(b) Optic nerve: It carries the reflection of the object from the retina to the brain. The image formed on the retina is in a reverted position and the correct picture is formed in the brain as the object is. The optic nerves arise from the side of diencephalon. They innervate the retina of the eye and are sensory in nature.
(c) Facial nerve: It carries message and all expressions of the face, mastication work alone by the teeth, movement of the neck and the activities of the salivary glands to the brain. It arises from the side of medulla. On the whole facial nerves are mixed in nature.

Long answer questions

Question 1.
With the help of a suitable diagram describe the structures of a neuron.
Answer:
Nervous system consists of special cells called nerve cells or neurons. It has a main cell body called cyton. It gives out many processes called dendrites. From it a very long process is given out. It is called axon or nerve fibre.
Selina Concise Biology Class 8 ICSE Solutions – Nervous System 2
The cell body has a nucleus. The dendrites get the message from the organs and send this message to the axon through the cell body. Then the axon sends the message to muscles to contrast or to the gland for secretion.
The neurons make contact with one another through their processes. The axon at its end branches and meets the dendrites of another neuron. The meeting point is called synapse. The message is passed on from one axon to the dendrites of another neuron. How the message goes ? It is like this:
Organ → Message goes to dnedrites → Cell body → Axon → Muscles or glands

Question 2.
Briefly describe the structure of the cerebrum in human brain and mention its functions.
Answer:
Brain consists of main three parts and lies in the cranial cavity of skull.

  1. The cerebrum
  2. The cerebellum
  3. The medulla oblongata

Cerebrum: It is very large and form two third of the whole brain. The two hemispheres are separated from each other by a deep longitudinal groove, the median fissure. The outer surface is folded with ridges and grooves. The hemispheres are hollow from inside and their walls have outer and inner portions. The outer portion has cell bodies of the neurons and it is called grey matter.
The wavery edges of the folded layer has large number of neurons to the extent of nine billion. The inner portion of the cerebrum has axons and it is called white matter.

Functions:

  1. It controls all the voluntary activities.
  2. It is the seat of intelligence, consciousness and will power.

Question 3.
Mention the three functions of spinal cord.
Answer:
Spinal cord has the following functions.

  1. It is the centre of reflex actions below the neck.
  2. It carries messages from the skin and muscles to the brain.
  3. All the stimuli and responses are passed from and to the brain through the spinal cord.

Question 4.
With the help of suitable example, describe reflex action.
Answer:
Reflex action: Reflex actions are automatic responses to stimuli. These actions are not under the control of the animal. They are of definite and mechanical type. Peripheral nervous system and spinal cord both control certain action and the brain is not in action.
Some examples of reflex actions are:

  1. Pupil becomes narrow when strong light falls on it.
  2. The aroma of the food makes the mouth watering.
  3. The hand is withdrawn as we touch the hot plate.
  4. Flow of bile from the gall bladder into the duodenum.
  5. A loud thud may lead to opening of the mouth.

In a reflex action brain is not involved, removing the hand on touching a hot plate is a reflex action. The impulse of heat goes from the hand to the spinal cord and the order is sent back to the muscles of the hand to remove the hand from the hot plate.

Question 5.
Describe three kinds of nerves, giving the example of each.
Answer:
A nerve is formed by a group of nerve fibres (axons) encased by tubular medullary sheath. The medullary sheath acts as insulation and do not allow mixing up of impulses of the neighbouring axons (nerve fibres) We have three kinds of nerves:

Selina Concise Biology Class 8 ICSE Solutions – Nervous System 3

  1. Sensory nerve: It brings impulses from sense organs as these have sensory fibres. These nerve carry the impulses from the sense organs to the brain or to the spinal cord as optic nerve of the eye.
  2. Motor nerves: These carry impulses to muscles or glands from the brain or spinal cord. These nerves have only motor fibres as nerves to the muscles of the eye ball.
  3. Mixed nerve: It has both sensory and motors fibres as nerve going to the tongue.

Question 6.
Differentiate between natural reflex and conditioned reflex. Give examples to illustrate your answer.
Answer:
Natural reflex: It is one in which no previous experience or learning is required. These reflexes are inborn i.e. inherited from the parents.
Examples are

  1. Blinking, coughing, sneezing as these are protective reflexes
  2. Salivation, swallowing, peristalsis as it provides functional efficiency.
  3. Dilation of the eyes pupil to look in the dark and vice versa. It is muscular movement.
  4. Pushing along of swallowed food through the food canal. It is muscular movement.

Conditioned Reflex: It is one which develops during lifetime due to experience or learning.
Examples are:

  1. Watering of mouth (Salvination) at the sight of a tasty food.
  2. Surfing the channels while watching the television.
  3. Typing of a keyboard of a computer.
  4. Playing a musical instrument.