States of Matter
6 marks · NormalA student investigates how quickly a purple solid, potassium manganate(VII), spreads through water and compares this to how a coloured gas spreads through air.
Describe, using the particle model, what happens to potassium manganate(VII) when it is placed in water.
State what is meant by the term 'solute' in this experiment.
Explain why the potassium manganate(VII) spreads more slowly in water than a coloured gas spreads in air.
State what is meant by a 'saturated solution.'
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Potassium manganate(VII) particles (ions) leave the solid and move between the water particles. They gradually spread out into the water, moving from an area of high concentration to low concentration, eventually mixing evenly. · must show particle movement, mixing, diffusion
(b) The solute is the potassium manganate(VII) solid that is dissolving in the water. · must show solid, dissolves
(c) Particles in water move more slowly than in air and are closer together, so the potassium manganate(VII) diffuses more slowly than a gas does in air. There is less space for particles to move past each other in liquids. · must show speed comparison, closer particles/less space
(d) A saturated solution is one that contains as much dissolved solute as possible at that temperature, with some undissolved solute remaining. · must show maximum dissolved, undissolved present, at a given temperature
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Describes particle movement (potassium manganate(VII) particles/ions move through water)
M2 (a) · 1 mark · Mentions spreading out, diffusion, or movement from high to low concentration
B1 (b) · 1 mark · Identifies potassium manganate(VII) as the solute (solid that dissolves)
M3 (c) · 1 mark · States that particles in water/liquid move more slowly OR are closer together
A1 (c) · 1 mark · Correctly links this to slower diffusion in water/liquids than gases/air
B2 (d) · 1 mark · States a saturated solution has the maximum amount dissolved, with undissolved solute at a given temperature
Worked solution
a) When potassium manganate(VII) is placed in water, its particles (ions) leave the solid and move into the water. These particles spread out among the water particles, moving from a region of high concentration (near where added) to low concentration, until evenly mixed. This is diffusion.
b) In this experiment, the solute is the potassium manganate(VII) solid because it is dissolved by the water.
c) Diffusion is slower in water than in air because particles in a liquid move more slowly and are packed closer together than in a gas. There is less space between particles, so it takes longer for the potassium manganate(VII) to diffuse.
d) A saturated solution is a solution containing as much dissolved solute as possible at a particular temperature, with some undissolved solid remaining.