Kinetic theory and gas behaviourIB MYP Sciences: Subtopic test

1. 1
   A hospital stores oxygen gas in sealed steel cylinders in a room with an air-conditioning system. The gas particles inside each cylinder are in constant random motion.

   (a)

   What causes the pressure of the gas inside a sealed cylinder?

   [1 mark]

   • AThe gas particles attract each other
   • BThe weight of the gas particles pressing on the base
   • CThe gas particles colliding with each other
   • DThe gas particles colliding with the walls of the cylinder

   (b)

   The temperature of the storage room is 27 °C. What is this temperature on the Kelvin scale?

   [1 mark]

   • A246 K
   • B300 K
   • C327 K
   • D27 K

   (c)

   A cylinder is left in hot sunlight. Explain, in terms of particles, why the pressure of the gas inside it increases.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a kitchen in Mumbai, the smell of spices frying on the stove reaches the far side of the room within a minute. In the same kitchen, a drop of food colouring added to a glass of water slowly spreads until the whole glass is coloured, without anyone stirring it.

   (a)

   What is the name of the spreading of particles from where there are many to where there are fewer, caused by their random motion?

   [1 mark]

   • AEvaporation
   • BCondensation
   • CDiffusion
   • DCompression

   (b)

   Why does diffusion happen faster in the air than in the water?

   [1 mark]

   • AGas particles are far apart and weakly attracted, so they spread more easily
   • BGas particles are heavier than liquid particles
   • CGas particles are attracted more strongly to each other
   • DLiquid particles do not move

   (c)

   The cook finds that the smell of the spices spreads more quickly when the kitchen is warm. Explain this using the particle model.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A class investigates how temperature affects diffusion. They add one crystal of potassium manganate(VII) to a beaker containing 200 cm³ of water and time how long it takes for the purple colour to spread evenly through the water. They repeat the test with water at different temperatures.

   (a)

   State a testable hypothesis for this investigation, including a scientific reason.

   [3 marks]

   (b)

   The times taken for the colour to spread evenly were 240 s at 10 °C, 95 s at 30 °C, 40 s at 50 °C and 18 s at 70 °C. Describe the trend, evaluate whether the results support the hypothesis and suggest one improvement to the investigation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Gas particles are too small to see, but scientists have indirect evidence for them. In one demonstration, a student watches smoke particles in a small glass cell of air through a microscope and sees each speck of smoke jerk about at random. Gases also have practical uses: in many villages in India, families are being offered cylinders of liquefied petroleum gas (LPG), stored under pressure, to replace cooking over wood fires.

   (a)

   Explain how the movement of the smoke particles provides evidence that air is made of tiny particles that are in constant random motion.

   [6 marks]

   (b)

   Evaluate the switch from cooking over wood fires to using LPG cylinders in villages. Discuss the benefits and drawbacks for people and the environment, and reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions