States of matter and kinetic theoryIB MYP Chemistry: Subtopic test

1. 1
   In a science lesson in Lagos, students seal the nozzles of two identical syringes. One syringe holds 20 cm³ of air and the other holds 20 cm³ of water. When the students push each plunger in firmly, the air syringe squashes to about 5 cm³ but the water syringe hardly changes volume. The teacher then draws the particles in each syringe as small hard spheres.

   (a)

   Which statement describes the particles in the air in the syringe?

   [1 mark]

   • AParticles are touching each other and vibrate in fixed positions
   • BParticles are far apart and move randomly at high speed
   • CParticles are touching each other and slide past one another
   • DParticles are far apart and vibrate in fixed positions

   (b)

   The teacher draws the particles as small hard spheres. Which is a limitation of this particle model?

   [1 mark]

   • AIt cannot show that the particles are very small
   • BIt shows particles in a gas that are far apart
   • CIt shows the particles as solid spheres and does not show the forces between them
   • DIt shows that the particles in a liquid are touching

   (c)

   Explain why the water in the syringe hardly changes volume when the plunger is pushed.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A metal worker in Seoul heats a solid iron bar from 20 °C to 300 °C in a workshop. The bar becomes slightly longer but stays solid and keeps its shape. Later in the day the same bar is heated in a furnace until it melts.

   (a)

   What happens to the iron particles as the bar is heated from 20 °C to 300 °C while it stays solid?

   [1 mark]

   • AThey vibrate with more energy about their fixed positions
   • BThey stop vibrating and become still
   • CThey start to slide past each other
   • DThey move far apart and travel in straight lines

   (b)

   When the iron is heated in the furnace until it melts, which describes the particles in the molten iron?

   [1 mark]

   • AClose together in a regular pattern and only vibrating
   • BFar apart and moving randomly
   • CFar apart and sliding past each other
   • DClose together, in an irregular arrangement, moving past each other

   (c)

   Explain, using the particle model, why the iron bar becomes slightly longer when heated but stays solid.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students in Santiago want to test the hypothesis that a gas is more compressible than a liquid. They seal the nozzles of two identical 50 cm³ syringes, one filled with 50 cm³ of air and one with 50 cm³ of water. They place the same 5 kg mass on each plunger, wait until the plunger stops moving and read the volume. Safety glasses are worn throughout.

   (a)

   Identify the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   The students find that the air has been compressed from 50 cm³ to 12 cm³, but the water has only changed from 50 cm³ to 49.5 cm³. Describe how the results differ, explain them using the particle model, and suggest one improvement to the method.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Engineers at a bus company in Delhi are replacing petrol buses with buses that run on compressed natural gas (CNG). The CNG is stored as a gas squeezed into strong steel cylinders at very high pressure. Petrol is a liquid fuel stored in a tank at normal pressure. The city government wants to expand the CNG fleet and has asked the engineers to explain and justify the plan to the public.

   (a)

   Use the particle model to explain why a large amount of natural gas can be squeezed into a small steel cylinder, but the same amount of liquid petrol cannot be squeezed into a smaller volume.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of replacing petrol buses with CNG buses in the city, and reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions