Working with Solutions and Mixtures
ANSWERS
Key Terms:
saturated solutions , unsaturated solutions , solubility ,
supersaturated solutions , rate of dissolving
Review Questions:
ANSWER ON A SEPARATE SHEET OF PAPER
1. Explain the difference between saturated and unsaturated solutions.
In a saturated solution, no more solute will dissolve at a specific
temperature. In an unsaturated solution, more of the solute can be
dissolved at the same temperature.
2. Use the particle theory to explain why a solution reaches a saturation
point.
A solution reaches a saturation point when no more solute will dissolve
because all the solvent particles are already attracted to as many solute
particles as they can be. No additional solvent particles are available to
attract more solute particles.
3. Explain how a supersaturated solution is made.
A supersaturated solution is made by heating the solvent so that more
solute is able to dissolve, and then cooling the solution without stirring it.
The extra solute that dissolved at the higher temperature will remain
dissolved even though the solution cools back to room temperature.
4. What 3 things could you do to make a solid dissolve more quickly in
a liquid? Explain how each of these factors affects the rate of
dissolving.
To make a solute dissolve more quickly, you could increase the
temperature of the solvent, stir the mixture at a faster speed, or break the
solute into smaller pieces.
a) Increasing the temperature causes movement of the solvent particles to
increase.
b) Stirring the mixture also increases the motion of the solvent particles,
so the solute dissolves faster. The attractive forces of the solvent pulls in
the different particles of the solute more quickly.
c) By breaking the solute into smaller pieces, the amount of surface area
that is exposed to the solvent increases, and therefore the solute dissolves
faster.
5. Match the description in column A with the correct term in column
B.
A
B
------------------------------------------------------------------------------------------------------ solution that has all the solute it can
dissolve at a given temperature
- rate of dissolving
- solubility
- amount of a solute that can be dissolved
in a specific amount of solvent at a
given temperature
- unsaturated
- supersaturated
- solution that can dissolve more solute
at a given temperature
- time it takes for a solute to dissolve
in a solvent
- solution that contains more dissolved
solute than it can hold at any given
temperature
- saturated
6. Rock salt has very large crystals. A test tube contains a saturated
solution of salt water, and a single crystal of rock salt is added. Will the
crystal eventually dissolve? Explain your answer.
The crystal will not dissolve because the solution is saturated. The
solution has no more room to dissolve any more salt.
7. Which would dissolve faster, powdered sugar (very fine sugar), or
regular granulated sugar? Explain your answer using the particle
theory.
Powdered sugar would dissolve faster than granulated sugar. Since the
powdered sugar has smaller particles, there is more surface area exposed
to the solvent.
8. If you were given some large crystals of rock salt to dissolve, what
would you do to speed up the process?
To speed up the process, you could heat the solvent to increase its
temperature, stir the solution, or crush the large crystals of salt into
smaller pieces to increase the exposed surface area.
9. You have been given a solution of sodium thiosulphate in a test tube
and you are to determine if the solution is unsaturated, saturated, or
supersaturated. How would you conduct an experiment to find out what
type it is?
You could obtain one more crystal of sodium thiosulphate and drop it into
the test tube and observe the results. If the crystal dissolves, you had an
unsaturated solution. If the crystal will not dissolve, you had a saturated
solution. Finally, if after dropping the crystal into the test tube the
solution begins to crystallize, you had a supersaturated solution
10. At 0oC, the solubility of salt is 35.7g per 100g of water. How much
salt must be added to 50g of water to make a saturated solution at 0oC?
For 100g of water, it takes 35.7g of salt to make a saturated solution.
Therefore, since you only have 50g of water (half of 100g), it takes
17.85g of salt (half of 35.7g) to make a saturated solution.
11. The top rock layer of Niagara Falls is made of a kind of rock called
limestone. The solubility of limestone in water is 0.0007g per 100g of
water. With 200 000 000 tons of water going over the falls everyday,
1400 tons of limestone could be dissolved. However, only a tiny fraction
of this amount actually dissolves. Explain why.
Much of the water that goes over Niagara Falls never comes in contact
with the rock. The water is moving so quickly that it only has time to
dissolve a tiny fraction of the limestone.