Revision Library

revisionlibrary.co.uk

KS3 · Chemistry

K6 Particles and their Behaviour

AQA AQA KS3 Science - Chemistry · Calculator allowed · about 90 minutes

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Which state of matter has particles that are far apart and move quickly in random directions, filling any container they are put into?

A) Solid
B) Liquid
C) Gas
D) Plasma

Complete each sentence about the particle model by choosing the correct word(s).

(a)In a solid, particles are packed ______ together in a ______ pattern.(1)

(b)In a liquid, particles are close together but can ______ past each other.(1)

(c)In a gas, particles are ______ apart and move ______ in random directions.(1)

Name the change of state described in each part.

(a)Solid changing to liquid.(1)

(b)Liquid changing to gas.(1)

(c)Gas changing to liquid.(1)

(d)Liquid changing to solid.(1)

A rectangular metal block has a mass of 180 g and a volume of 24 cm^3.

(a)State the equation linking density, mass and volume.(1)

(b)Calculate the density of the metal block.(2)

(c)State the correct unit for your answer to part (b) if mass had instead been measured in kg and volume in m^3.(1)

Required practical activity. Chidinma is finding the density of an irregularly shaped stone. She records the mass of the stone as 64 g. She then places 50.0 cm³ of water into a measuring cylinder and lowers the stone in on a thread, fully submerging it. The water level rises to 74.0 cm^3.

(a)Describe how Chidinma should use the equipment to find the volume of the stone.(2)

(b)Calculate the volume of the stone from the readings given.(2)

(c)Calculate the density of the stone. Give your answer to 2 significant figures.(2)

(d)Suggest one source of error in this method and how it could affect the calculated density.(1)

A student says that a gas can be squeezed into a much smaller volume, but water (a liquid) cannot be squeezed very much at all.

(a)State how the spacing between particles in a gas compares with the spacing between particles in a liquid.(1)

(b)Use this idea to explain why a gas can be compressed but a liquid cannot.(2)

Required practical activity. Meera drops a single crystal of potassium permanganate into a beaker of cold water and does not stir it. She watches the beaker for 30 minutes.

(a)Describe what Meera would observe over the 30 minutes.(2)

(b)Explain this observation in terms of particle theory.(3)

(c)Predict and explain the effect on the rate of diffusion of repeating the experiment with warm water instead of cold water.(2)

A sample of a liquid has a volume of 250 cm³ and a mass of 0.275 kg.

(3)

This question is about gas pressure.

(a)State what causes gas pressure inside a sealed container.(1)

(b)A sealed, rigid container of gas is heated. Explain why the pressure of the gas increases.(2)

A student investigates how the volume of a fixed mass of gas affects its pressure, at a constant temperature. Their results are shown below.
Volume (cm³): 10, 20, 40
Pressure (kPa): 200, 100, ?

(a)State the pattern shown by the data in the table.(1)

(b)Calculate the missing pressure value when the volume is 40 cm³, using the fact that pressure x volume stays constant for a fixed mass of gas at constant temperature.(2)

(c)Use the particle model to explain why decreasing the volume of the container increases the pressure of the gas.(2)

State two things that happen to the particles of a solid when it is heated but has not yet started to melt.

(2)

Small gaps are deliberately left between sections of metal railway line when they are installed.

(a)State what happens to the spacing between the particles in the metal rail as its temperature increases.(1)

(b)Use this idea to explain why the gaps are left between the rail sections.(2)

Required practical activity. Kwame investigates the cooling curve of stearic acid. He records its temperature every 2 minutes as it cools.
Time (min): 0, 2, 4, 6, 8, 10, 12, 14, 16
Temperature (degC): 95, 85, 76, 70, 70, 70, 70, 62, 52

(a)Identify the melting point of stearic acid shown by this data.(1)

(b)Explain, in terms of particles, why the temperature stays constant between 6 and 12 minutes even though the substance is still cooling.(3)

(c)Describe the overall shape of the cooling curve from 0 to 16 minutes, referring to the steepness of the graph in each section.(2)

Solids, liquids and gases have very different densities and can be compressed to very different extents. Explain, using ideas about particles, why a gas can be squashed into a much smaller volume but a solid or a liquid cannot.

(6)

Which change of state is the reverse of condensation?

A) Melting
B) Evaporating
C) Freezing
D) Subliming

Aluminium has a density of 2.7 g/cm^3. Calculate the mass of an aluminium block with a volume of 50 cm^3.

(3)

Vegetable oil has a density of about 0.92 g/cm^3. Water has a density of 1.00 g/cm^3. Oil floats on top of water.

(a)State how the density of a liquid affects whether it floats on water.(1)

(b)Use the density values given and ideas about particles to explain why oil floats on top of water.(2)

The density of liquid water is 1000 kg/m^3. The density of steam at 100 degC is about 0.6 kg/m^3.

(a)Calculate how many times greater the volume of a fixed mass of water becomes when it turns into steam.(2)

(b)Use your answer to part (a) to explain, in terms of particle arrangement, why steam takes up so much more space than the same mass of liquid water.(2)

Freya watches a hot air balloon take off at a local fete. The balloon rises after the air inside its envelope is heated by a burner.

(a)State what happens to the air particles inside the balloon as they are heated, and what happens to the density of the air as a result.(2)

(b)Use this idea to explain why the hot air balloon rises into the air.(2)

For each statement, identify whether it is True or False. If a statement is false, give the correct version.

(a)Particles in a solid are arranged in a fixed, regular pattern.(1)

(b)Particles in a liquid have a fixed shape because they cannot move.(1)

(c)When a gas is cooled and turns into a liquid, this change is called condensing.(1)

(d)The particles themselves get bigger when a substance is heated.(1)

A jeweller called Priya has bought a gold-coloured bar and wants to check whether it is pure gold. The bar has a mass of 965 g. When lowered into a measuring cylinder containing 200 cm³ of water, the water level rises to 250 cm^3. The density of pure gold is 19.3 g/cm³ and the density of pure silver is 10.5 g/cm^3.

(a)Calculate the volume of the bar.(1)

(b)Calculate the density of the bar in g/cm^3.(2)

(c)Compare your answer to part (b) with the densities given and conclude whether the bar is likely to be pure gold, pure silver, or a mixture of the two metals. Justify your answer.(2)

(d)State one reason why measuring density is a useful test for identifying whether a material is a pure substance.(1)

Mark scheme · K6 Particles and their Behaviour

Question 1

B1 C cao
Answer: C) Gas

Question 2

(a) B1 closely (tightly) and regular (fixed), both needed, oe
(a) Answer: closely; regular
(b) B1 move (slide), oe
(b) Answer: move (slide)
(c) B1 far and quickly (fast), both needed, oe
(c) Answer: far; quickly

Question 3

(a) B1 melting cao
(a) Answer: Melting
(b) B1 evaporating (boiling), oe
(b) Answer: Evaporating (or boiling)
(c) B1 condensing cao
(c) Answer: Condensing
(d) B1 freezing (solidifying), oe
(d) Answer: Freezing

Question 4

(a) B1 density = mass / volume, oe (allow rearranged forms)
(a) Answer: density = mass / volume
(b) M1 density = 180 / 24
(b) A1 7.5 (g/cm³) cao
(b) Answer: 7.5 g/cm³
(c) B1 kg/m³ cao
(c) Answer: kg/m³

Question 5

(a) B1 lower the stone fully into the water on a thread so that it is completely submerged, without touching the sides
(a) B1 read the water level before and after adding the stone, at eye level from the bottom of the meniscus, and take the difference in readings as the volume, oe
(a) Answer: Fully submerge the stone on a thread and read the water level before and after; the difference in readings is the volume of the stone.
(b) M1 volume = 74.0 - 50.0
(b) A1 24.0 (cm³) cao
(b) Answer: 24.0 cm³
(c) M1 density = 64 / 24, ft from (b)
(c) A1 2.7 (g/cm³) awrt 2 sf, ft from (b)
(c) Answer: 2.7 g/cm³
(d) B1 any one of: air bubbles trapped on the stone would make the recorded volume too large, giving a density that is too low; parallax error when reading the meniscus could make the volume too big or too small; the stone touching the side of the cylinder could give an inaccurate reading, oe
(d) Answer: Air bubbles trapped on the stone's surface would make the recorded volume too big, giving a calculated density that is too low.

Question 6

(a) B1 particles in a gas are much further apart (more spread out) than particles in a liquid, oe
(a) Answer: Gas particles are much further apart than liquid particles.
(b) M1 gas particles have large spaces between them, and pushing them closer together reduces the volume by a large amount
(b) A1 liquid particles are already close together (touching), so there is almost no space left to reduce, oe
(b) Answer: A gas compresses easily because its particles have large spaces between them that can be pushed together; a liquid cannot compress because its particles are already close together with almost no space left to remove.

Question 7

(a) B1 purple colour spreads out from the crystal through the water
(a) B1 eventually the whole beaker becomes evenly (uniformly) coloured purple, without any stirring, oe
(a) Answer: The purple colour gradually spreads out from the crystal until the whole beaker of water is evenly coloured purple.
(b) M1 water particles and potassium permanganate particles are in constant, random motion
(b) M1 particles collide and move into the spaces between other particles, moving from a region of higher concentration to a region of lower concentration
(b) A1 this is called diffusion, and it continues until the particles are evenly spread throughout the water, oe
(b) Answer: The constantly moving particles of potassium permanganate spread out (diffuse) from an area of high concentration to low concentration through the randomly moving water particles, until they are evenly spread throughout the beaker.
(c) B1 diffusion would be faster in warm water
(c) B1 because the water particles have more kinetic energy and move faster, so they collide with and spread the potassium permanganate particles more quickly, oe
(c) Answer: Diffusion would be faster in warm water because the particles have more kinetic energy and move faster, spreading the colour through the beaker more quickly.

Question 8

M1 convert 0.275 kg to 275 g
M1 density = 275 / 250
A1 1.1 (g/cm³) cao
Answer: 1.1 g/cm³

Question 9

(a) B1 particles of the gas colliding with the walls of the container, oe
(a) Answer: Gas particles colliding with the walls of the container.
(b) M1 heating increases the kinetic energy of the gas particles, so they move faster, on average
(b) A1 the particles collide with the walls of the container more often and with greater force, increasing the pressure, oe
(b) Answer: Heating the gas increases the particles' kinetic energy so they move faster, hitting the container walls more often and with more force, which increases the pressure.

Question 10

(a) B1 as the volume increases the pressure decreases (they are inversely proportional), oe
(a) Answer: As volume increases, pressure decreases (the two are inversely proportional).
(b) M1 pressure x volume = 200 x 10 = 2000 (kPa cm³), so pressure = 2000 / 40
(b) A1 50 (kPa) cao
(b) Answer: 50 kPa
(c) B1 the same number of gas particles is now contained in a smaller volume, oe
(c) B1 so the particles collide with the walls of the container more often (in a given time), increasing the pressure, oe
(c) Answer: The same number of particles is squeezed into a smaller space, so the particles collide with the container walls more frequently, increasing the pressure.

Question 11

B1 the particles gain kinetic energy and vibrate more (vibrate faster/more vigorously), oe
B1 the particles stay in their fixed positions/arrangement (they do not move from place to place), oe
Answer: The particles gain kinetic energy and vibrate more vigorously, but they stay in their fixed positions.

Question 12

(a) B1 the particles vibrate more and take up (slightly) more space, so the average spacing between them increases, oe
(a) Answer: The particles vibrate more and take up slightly more space, so the average spacing between them increases.
(b) M1 in hot weather the metal expands (gets longer) as the particles take up more space
(b) A1 the gaps allow room for this expansion, so the rails do not buckle/bend under the compressive force, oe
(b) Answer: In hot weather the rail expands as its particles take up more space; the gaps leave room for this expansion so the rails do not buckle.

Question 13

(a) B1 70 (degC) cao
(a) Answer: 70 degC
(b) M1 during this time the substance is changing state from liquid to solid (freezing), oe
(b) M1 energy is still being transferred away from the substance, but this energy is lost as the particles move closer together and form a regular arrangement, rather than from a decrease in their kinetic energy
(b) A1 so the average kinetic energy of the particles (and therefore the temperature) does not fall until freezing is complete, oe
(b) Answer: The substance is freezing during this time. Energy is still being removed, but it comes from the particles forming a more ordered, closer arrangement rather than from a fall in their kinetic energy, so the temperature stays constant until freezing is complete.
(c) M1 the temperature falls steadily (a sloped line) from 95 degC to 70 degC between 0 and 6 minutes, as the liquid cools
(c) A1 the line is then flat (horizontal) from 6 to 12 minutes as the substance freezes, before falling steadily again (a sloped line) from 70 degC to 52 degC between 12 and 16 minutes, as the solid cools, oe
(c) Answer: The curve falls steadily as the liquid cools (0 to 6 minutes), becomes flat at 70 degC while it freezes (6 to 12 minutes), then falls steadily again as the solid cools (12 to 16 minutes).

Question 14

Level 1 (1-2): Basic, isolated statements are made about the arrangement or spacing of particles in one or two states, with little or no explanation linked to compressibility.
Level 2 (3-4): A clear description is given of particle arrangement and spacing in at least two states, with some explanation linking spacing to ease (or difficulty) of compression.
Level 3 (5-6): A full, logically linked explanation of particle arrangement, spacing and energy in solids, liquids and gases is given, clearly explaining why gases compress easily (large spaces between fast-moving particles) while solids and liquids do not (particles already close together, with little space to reduce).
Indicative content:
- In a solid, particles are arranged in a fixed, regular pattern, very close together (touching), and only vibrate about fixed positions.
- In a liquid, particles are close together (similar spacing to a solid) but arranged randomly and are free to move/slide past each other.
- In a gas, particles are far apart, with large spaces between them, and move quickly in random directions.
- Because solid and liquid particles are already touching or very close together, there is almost no space between them to remove, so they cannot be compressed by very much.
- Because gas particles have large spaces between them, pushing the particles closer together reduces the volume by a large amount, so gases can be compressed easily.
- Density depends on how much mass is packed into a given volume; because gas particles are spread far apart, gases have a much lower density than the same substance as a solid or liquid.
- A correct, explicit link is made between reduced particle spacing under pressure and reduced volume, specifically for the gas state.

Question 15

B1 B cao
Answer: B) Evaporating

Question 16

M1 rearrange to mass = density x volume
M1 mass = 2.7 x 50
A1 135 (g) cao
Answer: 135 g

Question 17

(a) B1 a liquid with a lower density than water will float on top of water, oe
(a) Answer: A liquid that is less dense than water will float on top of it.
(b) M1 a given volume of oil contains less mass than the same volume of water (fewer/less tightly packed particles for the same volume), so oil is less dense than water
(b) A1 because oil (0.92 g/cm³) is less dense than water (1.00 g/cm³), a given volume of oil weighs less than the same volume of water, so the oil floats on top, oe
(b) Answer: Oil is less dense than water because the same volume of oil has less mass; since a given volume of oil weighs less than the same volume of water, the oil floats on top.

Question 18

(a) M1 for the same mass, volume ratio = density of water / density of steam = 1000 / 0.6
(a) A1 awrt 1670 (accept 1660 to 1680) times greater
(a) Answer: Approximately 1670 times greater (accept 1660 to 1680)
(b) M1 the particles are much further apart (more spread out) in steam than in liquid water, ft from (a)
(b) A1 because the same mass/number of particles now occupies a much greater volume, the particles must be spread over a much larger average distance from each other in the gas, matching the very large volume ratio found in (a), oe
(b) Answer: The particles in steam are spread much further apart than in liquid water; because the same mass of particles now fills a volume around 1670 times greater, the average spacing between particles must be far larger in the gas state.

Question 19

(a) B1 the air particles gain kinetic energy and move faster/further apart, so the air expands, oe
(a) B1 as the same mass of air now occupies a larger volume, its density decreases, oe
(a) Answer: The heated air particles move faster and spread further apart, so the air expands; since the same mass now fills a larger volume, its density decreases.
(b) M1 the heated air inside the balloon is less dense than the cooler air outside the balloon, ft from (a)
(b) A1 because the balloon (and the less dense air inside it) is less dense than the surrounding air, it experiences an upward force and rises, similar to a less dense object floating in a denser fluid, oe
(b) Answer: The heated air inside the balloon is less dense than the cooler air outside; because it is less dense than its surroundings, the balloon experiences an upward force and rises.

Question 20

(a) B1 True cao
(a) Answer: True
(b) B1 False; particles in a liquid can move/slide past each other, so a liquid takes the shape of its container, oe
(b) Answer: False - liquid particles can move/slide past each other, so a liquid takes the shape of its container.
(c) B1 True cao
(c) Answer: True
(d) B1 False; particles do not get bigger, they move faster/vibrate more and take up more space between them (the spacing increases, not the particle size), oe
(d) Answer: False - the particles do not get bigger; they move faster and spread further apart, so it is the spacing between them that increases.

Question 21

(a) B1 50 (cm³) cao
(a) Answer: 50 cm³
(b) M1 density = 965 / 50, ft from (a)
(b) A1 19.3 (g/cm³) cao, ft from (a)
(b) Answer: 19.3 g/cm³
(c) M1 the calculated density (19.3 g/cm³, ft from (b)) is very close to (matches) the density of pure gold (19.3 g/cm³), and is much higher than the density of pure silver (10.5 g/cm³)
(c) A1 so the bar is very likely to be pure gold (there is no evidence it is a silver mixture), oe
(c) Answer: The calculated density (19.3 g/cm³) matches the density of pure gold exactly and is far higher than silver's density, so the bar is very likely to be pure gold.
(d) B1 density is a fixed/characteristic property of a pure substance, regardless of the size or shape of the sample tested, oe
(d) Answer: Density is a fixed property of a pure substance, so the same value should be obtained no matter the size or shape of the sample tested.

Particles and their Behaviour - Worksheets, Questions and Revision