States of Matter
6 marks · NormalA teacher asks the class to consider a scenario: 'Chlorine gas and a solid sugar cube are each placed in the opposite ends of two sealed glass tubes filled with air. Both tubes are left for several hours at room temperature.'
Explain what happens to the chlorine gas in terms of diffusion.
Describe what would happen to the sugar cube over time and give a reason using particle ideas.
State what is meant by a solution, referring to both the sugar experiment and the key terms 'solute' and 'solvent.'
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(a) The chlorine gas particles spread out and mix with the air particles along the tube by diffusion, moving from higher concentration near the source to lower concentration areas. · must show spreading, particle movement, from high to low concentration
(b) The sugar cube will slowly dissolve if any moisture is present, and the dissolved sugar will diffuse into the air (much more slowly than a gas), because the sugar particles have to break away from the solid and mix among the air or water particles. · must show slow process, needs particles to move away, much slower than gas
(c) A solution forms when a solute (sugar) dissolves in a solvent (water). In the sugar experiment, sugar is the solute and water (if present) is the solvent, forming a solution where the sugar is evenly mixed in the water. · must show define solution, identify solute and solvent, apply to context
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Marking points
M1 (a) · 1 mark · Describes chlorine gas particles spreading/mixing with air
A1 (a) · 1 mark · Mentions movement from high to low concentration or diffusion process
M2 (b) · 1 mark · Describes sugar cube dissolving (if moisture) or not dissolving (if no solvent present)
A2 (b) · 1 mark · Reason given with particle ideas (break away from solid, diffusion much slower than gas)
M3 (c) · 1 mark · Defines a solution as a solute dissolved in a solvent
A3 (c) · 1 mark · Identifies sugar as solute, water as solvent, and correctly applies to context
Worked solution
a) The chlorine gas particles move randomly and spread out from their starting point, mixing with air by diffusion. They move from a region of high concentration (near where added) to regions of lower concentration.
b) The sugar cube will dissolve slowly if moisture (water) is present; then, sugar particles will gradually spread among the water particles. This is a slower diffusion process than with gases because solids dissolve and then move as particles in the liquid.
c) A solution is a mixture in which a solute dissolves in a solvent. In this case, sugar is the solute, water is the solvent, and together they make a solution where the sugar is evenly spread out in the water.