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Questions Core curriculum 1 A large crystal of potassium manganate(VII) was placed in the bottom of a beaker of cold water, and left for several hours.
4 A cooling curve is the opposite of a heating curve. It shows how the temperature of a substance changes with time, as it is cooled from a gas to a solid. Here is the cooling curve for one substance:
crystal of potassium manganate(VII) a Describe what would be seen: i after five minutes ii after several hours b Explain your answers using the idea of particles. c Name the two processes that took place during the experiment.
Use the idea of particles to explain why: a solids have a definite shape b liquids fill the bottom of a container c you can’t store gases in open containers d you can’t squeeze a sealed plastic syringe that is completely full of water e a balloon expands as you blow into it.
3 Below is a heating curve for a pure substance. It shows how the temperature rises over time, when the substance is heated until it melts, then boils.
a What is the melting point of the substance? b What happens to the temperature while the substance changes state? c The graph shows that the substance takes longer to boil than to melt. Suggest a reason for this. d How can you tell that the substance is not water? f Sketch a rough heating curve for pure water.
a What is the state of the substance at room temperature (20 °C)? b Use the list of melting and boiling points on page 9 to identify the substance. c Sketch a cooling curve for pure water.
5 Using the idea of particles explain why: a the smell of burnt food travels through the house b when two solids are placed on top of each other, they do not mix c pumping up your bike tyres gives a smooth ride d smokers can cause lung damage in other people e heating a gas in a closed container will increase its pressure f a liquid is used in a car’s breaking system, to transfer the pressure from the brake pedal g poisonous gases from a factory chimney can affect a large area. 6 a Which of these are examples of diffusion? i a helium-filled balloon rising in air ii a hydrogen-filled balloon deflating, due to gas passing through the skin iii the smell of perfume from a person standing on the other side of a room iv sucking a drink from a bottle, using a straw v an ice lolly turning liquid when it is left out of the freezer vi the tea in the cup changing colour when you add milk, without stirring vii a light, coloured gas, spreading down through a gas jar viii a blue crystal forming a blue solution, when it is left sitting in a glass of water ix spraying paint from a spray can. b For one of the examples of diffusion, draw a diagram showing the particles before and after diffusion has taken place. © OUP: this may be reproduced for class use solely for the purchaser’s institute
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Extended curriculum 7 You can measure the rate of diffusion of a gas using this apparatus. The gas enters through the thin tube: hydrogen gas (H2) in
air plug of porous plaster 0
c Explain your answer to b. Use the term mass! d The molecules in carbon dioxide are heavier than those in nitrogen and oxygen. So what do you think will happen to the water in the measuring tube, when you use carbon dioxide? Explain your answer.
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water rising in tube
The measuring tube is sealed at the top with a plug of porous plaster. Air and other gases can diffuse in and out through the tiny holes in the plug. The water rises in the measuring tube if the chosen gas diffuses out through the plug faster than air diffuses in. Air is mainly nitrogen and oxygen. a When you use hydrogen gas, the water rises in the measuring tube. Why? b What does this tell you about the rate of diffusion of hydrogen, compared to the gases in air?
Relative atomic or molecular mass
Look at the table above. a Which two gases will mix fastest? Explain. b Which gas will take least time to escape from a gas syringe? c Would you expect chlorine to diffuse more slowly than the gases in air? Explain. d An unknown gas diffuses faster than nitrogen, but more slowly than methane. What you can say about its relative molecular mass?
ÂŠ OUP: this may be reproduced for class use solely for the purchaserâ€™s institute