Diffusion of Cobalt(II) Chloride in Water

Fig. 3.1 shows a coloured crystal of cobalt(II) chloride is placed at the bottom of a beaker containing water. After two days, the colour has spread throughout the water. This observation can best be explained by which process?

• Diffusion of cobalt(II) chloride particles throughout the water

• Evaporation of water from the beaker

• Condensation of water on the crystal

• Melting of cobalt(II) chloride in water

This question is about halogens. Bromine is a red-brown liquid. A drop of liquid bromine is placed in a gas jar. After 20 minutes the red-brown colour has spread throughout the gas jar. Which statement best explains these observations using the kinetic particle model?

• The bromine particles move from an area of high concentration to an area of low concentration by diffusion. The particles are in constant random motion due to their kinetic energy, which causes them to spread throughout the gas jar over time.

• The bromine particles remain stationary and do not move within the gas jar.

• The bromine particles only move when the gas jar is heated.

• The bromine particles settle at the bottom of the gas jar due to gravity.

This question is about the first 30 elements in the Periodic Table. Name the element which: (e) is the gas with the slowest rate of diffusion at room temperature (extended only)

• Argon

• Oxygen

• Nitrogen

• Neon

Identify the element which: (e) has the highest rate of diffusion at room temperature (extended only)

• Neon

• Argon

• Oxygen

• Nitrogen

This question is about gases found in clean, dry air and gases found in polluted air. (e) All gases diffuse. (i) Choose from the list of formulae the gas which diffuses most quickly. (extended only) Draw a circle around your answer.

• CO

• CO₂

• CH₄

• NO₂

• SO₂

All gases diffuse. Which gas diffuses most quickly?

• CH₄

• O₂

• CO₂

• N₂