Diffusion and gas behaviourIB MYP Chemistry: Subtopic test

1. 1
   A teacher in Johannesburg places cotton wool soaked in concentrated ammonia solution at one end of a long, horizontal glass tube, and cotton wool soaked in concentrated hydrochloric acid at the other end. Both ends are sealed with bungs. After a few minutes a ring of white solid (ammonium chloride) forms inside the tube, closer to the hydrochloric acid end than to the ammonia end.

   (a)

   What is the name of the process by which the ammonia and hydrogen chloride gases spread through the tube?

   [1 mark]

   • AEvaporation
   • BDiffusion
   • CCondensation
   • DSublimation

   (b)

   The teacher repeats the experiment with the tube in a warm room. What is the most likely result?

   [1 mark]

   • AThe ring forms exactly in the middle of the tube
   • BThe ring takes longer to form
   • CNo ring forms
   • DThe ring forms sooner because the particles have more kinetic energy

   (c)

   A particle of ammonia has a relative mass of 17 and a particle of hydrogen chloride has a relative mass of 36.5. Explain why the white ring forms closer to the hydrochloric acid end.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in Oslo uses a microscope to look at smoke in a small glass cell lit from the side. The student sees tiny bright specks of smoke ash that jiggle about in random, jerky paths, constantly changing direction. The specks never stop moving, even though the air in the cell is perfectly still.

   (a)

   What causes the smoke specks to move in random, jerky paths?

   [1 mark]

   • ACollisions with fast-moving air particles that are too small to see
   • BThe specks are being pushed by the light from the lamp
   • CThe specks have forces pulling them towards the glass
   • DThe specks are alive

   (b)

   What does this observation provide evidence for?

   [1 mark]

   • AAir is made of particles that never move
   • BSmoke is a liquid
   • CAir is made of tiny particles in constant random motion
   • DAll the particles in air move at exactly the same speed

   (c)

   Explain why the smoke specks move in random directions rather than in a straight line.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Wellington investigates how temperature affects diffusion in a liquid. She drops one small crystal of potassium manganate(VII), which is purple, into each of three beakers containing 200 cm³ of water at different temperatures, without stirring. She uses a stopwatch to time how long it takes for the purple colour to spread evenly through the water, judged by eye. She wears safety glasses throughout.

   (a)

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

   [3 marks]

   (b)

   The student records these times for the colour to spread evenly: 420 s at 10 °C, 190 s at 30 °C and 85 s at 50 °C. Describe the trend, state whether the results support the hypothesis and suggest one way to improve the reliability of the results.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A can of deodorant sold in Dubai carries the warning: 'Pressurised container. Do not expose to temperatures above 50 °C. Do not puncture or burn.' The can is sealed and rigid and contains a fixed amount of gas as well as the liquid product. Last summer a delivery driver left several cans in a van parked in direct sunshine, and one of them burst.

   (a)

   Explain, using the particle model, how the gas in the can exerts pressure and why the pressure increases when the can is heated.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of using pressurised aerosol cans for consumer products, and reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions