States of MatterCambridge IGCSE Chemistry: Topic test

20 questions, 54 marks

Cambridge IGCSE Chemistry

States of Matter topic test

Total 54 marks

Name

Class

Date

1
A student investigates a pure solid substance, X, with a known melting point of 80°C. The student heats a small sample of solid X slowly and steadily in a water bath, recording its temperature at regular time intervals as it changes from a solid into a liquid.
(a)
As the substance is heated, its temperature rises steadily and then remains constant for several minutes before rising again. What is happening to the substance during the period when its temperature stays constant?
[1 mark]
AIt is boiling, turning from a liquid into a gas
BIt is melting, turning from a solid into a liquid
CIt is subliming, turning directly from a solid into a gas
DIt is condensing, turning from a gas into a liquid
(b)
Which statement correctly compares the arrangement and movement of the particles in solid X just before melting with the particles in liquid X just after melting?
[1 mark]
AIn the solid the particles are held in fixed positions and only vibrate; in the liquid the particles are close together but can move past each other
BIn the solid the particles are far apart and move randomly; in the liquid the particles are close together and fixed in position
CThe particles in the solid and the liquid are arranged and move in exactly the same way
DIn the solid the particles move past each other freely; in the liquid the particles are held in fixed positions
(c)
Explain, in terms of kinetic particle theory, why the temperature of substance X stays constant while it is melting, even though it is still being heated.
[2 marks]
Total for question 1: 4 marks
2
A fixed mass of gas is trapped inside a sealed glass syringe fitted with a frictionless, gas-tight plunger. The syringe is connected to a pressure sensor and placed in a water bath so that its temperature can be controlled.
(a)
The plunger is pushed in, reducing the volume of the trapped gas to half its original value while the temperature is kept constant. What happens to the pressure of the gas?
[1 mark]
AIt stays the same, because the mass of gas has not changed
BIt decreases to half its original value
CIt increases, because the same number of particles now collide with the walls more frequently
DIt becomes zero, because the particles can no longer move
(b)
The plunger is returned to its original position and the water bath is then used to raise the temperature of the gas while its volume is kept constant. What happens to the pressure of the gas?
[1 mark]
AIt decreases, because the particles move more slowly at higher temperature
BIt increases, because the particles have more kinetic energy and collide with the walls more frequently and forcefully
CIt stays the same, because pressure does not depend on temperature
DIt increases only if the gas is changed for a denser gas
(c)
Explain, in terms of kinetic particle theory, why decreasing the volume of the trapped gas at constant temperature increases its pressure.
[2 marks]
Total for question 2: 4 marks
3
A single small crystal of purple potassium manganate(VII) is dropped gently into a beaker of still water and left undisturbed. Over the next hour, a purple colour is seen to spread slowly outwards from the crystal until it eventually colours the whole beaker of water.
(a)
Describe and explain, in terms of kinetic particle theory, how the purple colour spreads through the water even though the water is not stirred.
[3 marks]
(b)
The experiment is repeated with an identical crystal in a second beaker of water that is kept at a much higher temperature. Explain why the purple colour spreads through the hot water more quickly than through the water at room temperature.
[4 marks]
Total for question 3: 7 marks
4
A few drops of orange-brown liquid bromine are placed in the bottom of a gas jar, which is then sealed with a glass cover and left at room temperature. A second identical gas jar, filled only with air, is placed directly on top of the first, and the glass cover between them is carefully removed so the two jars form one connected space. Within a few minutes, the whole connected space is filled with a uniform pale orange-brown colour.
(a)
Explain fully, in terms of kinetic particle theory, the changes that take place from the moment the liquid bromine is placed in the sealed jar to the point where the colour is spread evenly through both jars.
[6 marks]
(b)
Predict and explain how the outcome of this experiment would differ if it were repeated at a much lower temperature, and separately, how it would differ if the bromine were replaced with an equal amount of a liquid that produces a much lighter vapour with a smaller relative molecular mass, at the same room temperature.
[6 marks]
Total for question 4: 12 marks
5
A technician melts a sample of pure candle wax completely in a beaker and then allows it to cool slowly at room temperature, recording its temperature at regular time intervals until it has completely solidified.
(a)
The recorded temperature falls steadily, then stays constant for several minutes, then falls steadily again. What is happening to the wax while its temperature is constant?
[1 mark]
AIt is boiling, turning from a liquid into a gas
BIt is condensing, turning from a gas into a liquid
CIt is freezing, turning from a liquid into a solid
DIt is subliming, turning from a solid into a gas
(b)
Which statement correctly describes how the arrangement of the wax particles changes as the wax freezes?
[1 mark]
AThe particles move further apart and become completely free to move in any direction
BThe particles become held in fixed positions in a regular, closely packed arrangement, only vibrating about those positions
CThe particles stop moving completely and no longer possess any energy
DThe particles gain enough energy to escape from each other entirely
(c)
Explain, in terms of kinetic particle theory, why the temperature of the wax remains constant while it is freezing, even though it is still losing thermal energy to its surroundings.
[2 marks]
Total for question 5: 4 marks
6
A fixed mass of air is trapped inside a bicycle pump with the outlet sealed shut, so the trapped air cannot escape. The temperature of the air is kept constant throughout.
(a)
The handle of the pump is pulled outward, increasing the volume of the trapped air to twice its original value. What happens to the pressure of the trapped air?
[1 mark]
AIt doubles
BIt stays the same
CIt becomes zero
DIt decreases to about half its original value
(b)
The handle is then pushed firmly back in, reducing the volume of the trapped air to well below its original value. Which statement correctly explains, in terms of kinetic particle theory, why the pressure of the trapped air increases?
[1 mark]
AThe particles of air are destroyed as the volume decreases, releasing energy as pressure
BThe same number of particles are confined to a smaller space, so they collide with the walls of the pump more frequently
CThe particles of air turn into a liquid, which exerts a higher pressure than a gas
DThe particles move further apart, reducing the number of collisions with the walls
(c)
Explain, in terms of kinetic particle theory, why increasing the volume available to the trapped air, at constant temperature, decreases its pressure.
[2 marks]
Total for question 6: 4 marks
7
A student pours a layer of clear, still agar gel into a shallow dish and allows it to set. A single drop of blue dye is placed at the centre of the gel's surface. Without any stirring, the student measures the radius of the blue circle that spreads outward from the drop at regular time intervals.
(a)
Describe how the radius of the blue circle is expected to change over time, and explain this observation in terms of kinetic particle theory.
[3 marks]
(b)
The experiment is repeated with an identical dish of gel kept at a much lower temperature than the first. Explain why the radius of the blue circle increases more slowly in the colder gel.
[4 marks]
Total for question 7: 7 marks
8
A few grey-black crystals of solid iodine are placed in the bottom of a sealed gas jar filled with air, and the jar is warmed gently on a hotplate without reaching iodine's melting point. A deep purple vapour is seen to appear above the crystals and gradually spread until it fills the whole gas jar with an even purple colour.
(a)
Explain fully, in terms of kinetic particle theory, the changes that take place from the moment the iodine crystals are gently warmed to the point where the purple colour fills the gas jar evenly.
[6 marks]
(b)
Hydrogen gas, which has a much smaller relative molecular mass than iodine vapour, is released at the same time from a point source in a second identical gas jar at the same temperature. Predict and explain how the rate at which the hydrogen spreads through its jar compares with the rate at which the iodine vapour spread through its jar, and explain how this comparison would change if the second jar were instead kept at a much higher temperature than the first.
[6 marks]
Total for question 8: 12 marks

End of questions