Condensation

Methods Of Separation Of Substances Under Wet Conditions

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Methods Of Separation Of Substances Under Wet Conditions

Some solid particles are insoluble in water. For example chalk powder, dust particles, sand, and tiny pieces of straw are insoluble in water. To separate this type of particles generally we use the following methods

Sedimentation and Decantation

Have you seen pulses being washed in your home? When pulses are kept in a bowl of water, they settle down as they are heavy. However, dirt, insects, tiny pieces of straw, and other lighter impurities float at the top. The water, which contains these impurities, is then poured out and discarded. This process involves two methods: sedimentation and decantation.

The process of separating insoluble solids, suspended in a liquid, by allowing them to settle down is called sedimentation. The solid particles that settle down during sedimentation are called sediments. The process of pouring out the clear upper liquid without disturbing the sediments is called decantation. The liquid above the sediments is called a supernatant.

Methods Of Separation Of Substances Under Wet Conditions 1A mixture of sand and water can also be separated by sedimentation and decantation. The mixture is left undisturbed for some time. Sand, being heavier, settles down and water is poured out into a separate container.

Activity Aim: To observe cleaning of rice by sedimentation and decantation.
Materials needed: A cup of rice and a bowl of water.
Method:

  1. Observe the rice and record your observations. Does the rice look dirty?
  2. Now, mix the rice with water in a bowl and allow it to stand for something.
  3. Without disturbing the layer of rice, decant the water.

Observation: When the mixture is allowed to stand, most impurities came up and floated near the surface, whereas the rice settled down. On decanting the water, we got cleaner rice.
Conclusion: Rice can be cleaned by sedimentation and decantation.

Filtration

The process by which two substances (an insoluble solid and a liquid) are separated by passing the mixture through a filtering device is called filtration.

Filtration is commonly used in our homes. For example, after preparing tea, we filter out the tea leaves using a strainer. Filtration is also done to remove pulp from fresh fruit juice. Water may also contain solid impurities, which can be removed by filtration.

During filtration, the insoluble solid is retained in the filtering device whereas the liquid passes through it. It is important that the particles of the insoluble solid are bigger than the holes in the filtering device for them to be retained in it. A filter paper is a filtering device that has very fine pores in it.

Activity

Aim: To separate a mixture of sand and water by filtration.
Materials needed: Mixture of sand and water, funnel, beaker, flask, and filter paper.
Method:

    1. Fold the piece of filter paper twice to make a cone.
    2. Keep this filter paper cone inside the funnel. Place the funnel into the flask.
    3. Pour the mixture into the flask through the funnel.

Methods Of Separation Of Substances Under Wet Conditions 2

Observation: It is observed that sand is retained in the filter paper but water passes through.
Conclusion: Sand and water can be separated by filtration.

Evaporation

 

The process in which a liquid changes into a gas is called evaporation. In this method, the mixture is heated. The liquid part of the mixture evaporates leaving the solid part behind. For example, a mixture of common salt and water can be separated by evaporation. In fact, evaporating seawater is one of the oldest ways of obtaining salt.

Methods Of Separation Of Substances Under Wet Conditions 3

salt-from-seawater
Fig. Obtaining salt from seawater

Activity

Aim: To separate a mixture of salt and sand.
Materials needed: Mixture of salt and sand, filter paper, burner; test tube, test tube holder and water.
Method:

  1. Take the mixture of salt and sand in a test tube. Add water to it and shake it well.
  2. Salt dissolves in water, whereas sand does not. Sand can be separated using a filter paper.
  3. Now, only salt solution remains in the test tube.
  4. Heat the salt water till all the water changes to vapour, leaving the salt behind.

Observation: Salt is left behind in the test tube.
Conclusion: Two processes, filtration and evaporation, were used to separate a mixture of salt and sand. Thus, sometimes more than one method can be used to separate the components of a mixture.

Condensation

The process in which gas changes into liquid is called condensation. Condensation is the opposite of evaporation. In nature, water vapour in the air condenses to form its liquid form, the dew. Condensation takes place only when water vapour hits a cold surface.

Activity

Aim: To separate both water and salt from saltwater.
Materials needed: Saltwater, kettle, metal plate, a pair of tongs, bowl and burner.
Method:

    1. Take saltwater in the kettle and heat it over the burner.
    2. After some time, steam comes out of the spout of the kettle.
    3. Hold the metal plate (using tongs) above the spout. The steam condenses and changes into water droplets on touching the plate (cold surface).
    4. Collect the falling water drops in the bowl.
    5. Heat until all the water has boiled off.

Methods Of Separation Of Substances Under Wet Conditions 4

Observation: Salt is left behind in the kettle and water is collected in the bowl.
Conclusion: Water and salt could be separated from saltwater by the process of evaporation and condensation.

How does the Temperature Affect the Movement of Particles

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How does Temperature Affect the Movement of Particles

Effect of Temperature Change
By increasing the temperature (by heating), a solid can be converted into the liquid state; and the liquid can be converted into a gaseous state (or vapour state). And by decreasing the temperature (by cooling), a gas can be converted into a liquid state; and a liquid can be converted into solid-state. Students can know more about how does temperature affect the motion of particles and how does temperature affect particle movement. How does heating and cooling affect the movement of particles, movement of particles are dependent on temperature.

1. Solid to liquid change : Melting
Defination : The process in which a solid substance changes into   a liquid on heating, is called melting (or fusion).
Melting point : The temperature at which a solid substance melts and changes into a liquid at atmospheric pressure, is called melting point of the substance.
Ice is a solid. In solids, the particles are tightly packed together. When we heat a solid, its particles become more energetic and kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating more strongly with greater speed. The energy supplied by heat overcomes the intermolecular forces of attraction between the particles. As a result, the particles leave their mean position and break away from each other. When this happens, the solid melts and a liquid is formed.
Ex. Melting point of ice = 0ºC
Melting point of wax = 63ºC
Melting point of iron = 1535ºC
The melting point of a solid is a measure of the force of attraction between its particles. Higher the melting point of a solid substance, greater will be the force of attraction between its particles.
How does the Temperature Affect the Movement of Particles 12. Liquid to gas change : Boiling (or vaporisation)
Defination : The process in which a liquid substance changes into a gas rapidly on heating, is called boiling.
Boiling point : The temperature at which a liquid boils and changes rapidly into a gas at atmospheric pressure, is called boiling point of the liquid.
In a liquid most of the particles are close together. When we supply heat energy to the liquid, the particles of water start vibrating even faster. Some of the particles become so energetic that they can overcome the attractive forces of the particles around them. Therefore, they become free to move and escape from the liquid. When this happens, the liquid evaporates i.e., starts changing into gas.
Ex.       Boiling point of water = 100ºC
Boiling point of alcohol = 78ºC
Boiling point of mercury = 357ºC
The boiling point of a liquid is a measure of the force of attraction between its particles. Higher the boiling point of a liquid, greater will be the force of attraction between its particles.
When a liquid is heated, the heat energy makes its particles move even faster. At the boiling point the particles of a liquid have sufficient kinetic energy to overcome the forces of attraction holding them together and separate into individual particles. And the liquid boils to form a gas.

3. Gas to liquid change : Condensation
The process of changing a gas to a liquid by cooling, is called condensation. Condensation is the reverse of boiling.

4. Liquid to solid change : Freezing
The process of changing a liquid into a solid by cooling, is called freezing. Freezing means solidification. Freezing is the reverse of melting. So, the freezing point of a liquid is the same as the melting point of its solid form.
Ex.       Melting point of ice = 0ºC
Freezing poing of water = 0ºC

What is meant by the Kinetic Theory of Matter?

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What is meant by the Kinetic Theory of Matter?

The Kinetic Theory of Matter:

  1. The arrangement and movement of particles in solids, liquids and gases are described in the kinetic theory of matter.
  2. The kinetic theory of matter is used to explain the changes in the states of matter.
  3. The changes in the states of matter are caused by heating or cooling. For example, ice melts when it is heated and water changes into ice when it is frozen.
  4. The kinetic energy of particles increases during heating.
  5. The kinetic energy of particles decreases during cooling.

Arrangement and movement of particles in a gas:

  • Arrangement of particles:
    The particles are very far apart from each other and are in a random arrangement.
  • Forces of attraction between particles:
    There are weak forces between the particles. Movement of particles The particles can vibrate, rotate and move freely. The rate of collision is greater than the rate of collision in a liquid.
  • Energy content of particles:
    Highest energy content as movement is at random.
  • Why does a gas not have a fixed shape or volume?
    Gas can be easily compressed because the particles have more space between them compared to the particles of liquids or solids. Thus, it has no fixed shape or volume.

What is meant by the Kinetic Theory of Matter 1

Arrangement and movement of particles in a liquid:

  • Arrangement of particles:
    The particles are packed closely together but not in an orderly arrangement.
  • Forces of attraction between particles:
    The particles are held together by strong forces but weaker than the forces in a solid.
  • Movement of particles:
    The particles can vibrate, rotate and move throughout the liquid. They collide against each other.
  • Energy content of particles:
    Higher energy content as particles can move easily.
  • A liquid cannot be compressed easily because the particles are packed closely even though are arranged k in disorderly manner. Thus, it has a fixed volume.
  • It does not have a fixed shape but takes the shape of the container.

People also ask

Arrangement and movement of particles in a solid:

  • Arrangement of particles:
    The particles are packed closely together in an orderly manner.
  • Forces of attraction between particles:
    There are strong forces between the particles.
  • Movement of particles:
    The particles can only vibrate and rotate about their fixed positions.
  • Energy content of particles:
    Low energy content as movement is restricted.
  • Why does a solid have a fixed shape or volume?
    A solid cannot be compressed because its particles are very close to one another. Thus, it has a fixed shape or volume.

How can you change matter from one state to another?

Changes in the states of matter:
What is meant by the Kinetic Theory of Matter 2Boiling/Evaporation:

  • When a liquid is heated, the particles of the liquid gain kinetic energy and move faster as the temperature increases.
  • Eventually, the particles have enough energy to completely break the forces holding them together.
  • The particles are now able to move freely and far apart.
  • A gas is formed. The temperature at which this happens is called the boiling point.
  • The boiling point is the temperature at which a liquid changes into A a gas at a particular pressure.

Sublimation:

  • Sublimation is a process by which a solid changes directly into a gas without passing through the liquid state.
  • Examples of substances that undergo sublimation are iodine, ammonium chloride, NH4Cl and dry ice (solid carbon dioxide).

Freezing:

  • When a liquid is cooled, the particles in the liquid lose energy and move slower.
  • As the temperature continues to drop, the particles continue to lose more energy until they do not have enough energy to move freely.
  • At this point, the liquid changes into a solid.
  • The temperature at which this happens is called the freezing point.
  • The freezing point is the temperature at which a liquid changes into a solid at a particular pressure.

Condensation:

  • When a gas is cooled, the particles in the gas lose energy and move slower.
  • As the temperature drops, the gas particles lose energy and M move more slowly.
  • Eventually, the movements of the particles become slow enough for the gas to change into a liquid.
  • This change occurs at the boiling point of the substance.

Melting:

  • When a solid is heated, X the particles in the solid gain kinetic energy and vibrate more vigorously.
  • The particles vibrate faster as the temperature increases until the energy they gain is able to overcome the forces, that hold them at their fixed positions.
  • At this point, the solid becomes a liquid.
  • The temperature at which this happens is called the melting point.
  • The melting point is the temperature at which a solid changes into a liquid at a particular pressure.

Melting and Freezing points of Naphthalene Experiment

Aim: To determine the melting and freezing points of naphthalene.
Materials: Naphthalene and tap water.
Apparatus: Boiling tube, 250 cm3 beaker, thermometer, tripod stand, retort stand and clamp, Bunsen burner, stopwatch, conical flask and wire gauze.
Procedure:
A. Heating of naphthalene

  1. A boiling tube is filled with naphthalene to a depth of 3 cm and a thermometer is put into it.
  2. The boiling tube is suspended in a beaker half-filled with water using a retort stand and a clamp as shown in Figure A. The level of naphthalene in the boiling tube is ensured to be below the level of water in the beaker.
    What is meant by the Kinetic Theory of Matter 3
  3. The water is heated and the naphthalene (highly flammable) is stirred slowly with the thermometer.
  4. When the temperature of the naphthalene reaches 60°C, the stopwatch is started. The temperature and the state(s) of the naphthalene are recorded at half-minute intervals until the temperature of the naphthalene reaches 90°C.

B. Cooling of naphthalene

  1. The boiling tube in section A is removed from the water bath. The outer surface of the boiling tube is dried and immediately it is put in a conical flask, as shown in Figure B. The naphthalene is stirred continuously.
    What is meant by the Kinetic Theory of Matter 4
  2. The temperature and state(s) of the naphthalene are recorded at half¬minute intervals until the temperature drops to about 60°C.

Results:

Heating of naphthaleneCooling of naphthalene
Time (min)Temperature (°C)StateTime (min)Temperature (°C)State
0.061.0Solid0.087.0Liquid
0.565.0Solid0.584.0Liquid
1.067.0Solid1.083.0Liquid
1.571.0Solid1.581.0Liquid
2.074.0Solid2.080.0Liquid and solid
2.576.0Solid2.580.0Liquid and solid
3.079.0Solid3.080.0Liquid and solid
3.580.0Solid and liquid3.580.0Liquid and solid
4.080.0Solid and liquid4.080.0Liquid and solid
4.580.0Solid and liquid4.580.0Liquid and solid
5.080.0Solid and liquid5.080.0Liquid and solid
5.580.0Solid and liquid5.576.0Solid
6.080.0Solid and liquid6.073.0Solid
6.583.0Liquid6.569.0Solid
7.086.0Liquid7.066.0Solid
7.589.0liquid7.564.0Solid

Discussion:

  1. A graph of temperature against time is plotted for the heating of naphthalene, as shown in Figure C.
    What is meant by the Kinetic Theory of Matter 5
  2. Notice that there is a certain part of the curve where there is no change in the temperature with time during heating. At this temperature, both solid and liquid are present. It is the melting point of naphthalene. Hence, the melting point of naphthalene is 80.0°C.
    (a) At point A, naphthalene exists as a solid.
    (b) When the solid is heated, heat energy is absorbed. This causes the particles to gain kinetic energy and vibrate faster. The temperature increases from point A to point 8.
    (c) At point 8, solid naphthalene begins to melt. During the melting process, the temperature of naphthalene does not rise even though heating continues. The temperature remains constant because the heat energy absorbed by the particles is used to overcome the forces between particles so that the solid can turn into a liquid. At this temperature, both solid and liquid are present.
    (d) At point C, all the solid naphthalene has melted.
    (e) From point C to point D, the particles in liquid naphthalene absorb heat energy and move faster. The temperature increases from point C to point D.
  3. A graph of temperature against time is plotted for the cooling of naphthalene, as shown in Figure D.
    What is meant by the Kinetic Theory of Matter
  4. Notice that, there is a certain part of the curve where the temperature is constant with time during the cooling. At this temperature, both solid and liquid are present. It is the freezing point of naphthalene. Hence, the freezing point of naphthalene is 80.0°C.
    (a) At point E, naphthalene exists as a liquid.
    (b) When the liquid is cooled, the particles in the liquid lose their kinetic energy. They move slower as the temperature decreases from point E to point F.
    (c) At point F, liquid naphthalene begins to freeze. During the freezing process, the temperature of naphthalene remains constant because the heat loss to the surroundings is exactly balanced by the heat energy liberated as the particles attract one another to form a solid. At this temperature, both solid and liquid are present.
    (d) At point C, all the liquid naphthalene has frozen.
    (e) From point C to point H, the particles in solid naphthalene release heat energy and vibrate slower. The temperature decreases from point C to point H.
  5. During the heating of naphthalene,
    (a) a water bath is used instead of direct heating with a Bunsen flame. This is to ensure that the naphthalene is
    heated evenly. Furthermore, the naphthalene is flammable.
    (b) the naphthalene is stirred continuously to ensure an even heating.
  6. During the cooling of naphthalene,
    (a) the boiling tube containing liquid naphthalene is placed in a conical flask. This is to ensure an even cooling process and to minimise heat loss to the surroundings.
    (b) the naphthalene is stirred continuously to avoid supercooling.
    Supercooling is a condition in which the temperature of a cooling liquid drops below its normal freezing point, without the appearance of a solid.
    What is meant by the Kinetic Theory of Matter 6
  7. A water bath is used in this experiment because the melting point of naphthalene is below 100°C, the maximum temperature that can be attained by the water bath. For solids with melting points above 100°C, a liquid with a higher boiling point than water such as oil must be used.

Conclusion:
The melting and freezing points of naphthalene are the same, that is 80.0°C.