Name: _________________________________________ Date: _______________ Period: ____
Comparing Solubilities and Rates of Dissolving
Background Information
When one substance dissolves in another, the mixture is called a solution. The substance
that dissolves is the solute. A substance that dissolves other substances is called a solvent. The
rate at which a solid solute dissolves depends on several factors including temperature, stirring,
and the surface area of the solute. Solubility is the maximum amount of a solute that can dissolve
in a given amount of a solvent at a certain temperature. The solubility of different substances
varies, but it is always the same for a given substance at a given temperature.
In this investigation, you will determine the effect of surface area on the rate at which
NaCl dissolves in water. You will also investigate how temperature affects the solubility of
ammonium chloride in water.
Materials
Rock Salt
Stop Watch
Table Salt
Stirring Rods
Paper Towel
Thermometer
NH4Cl
150 mL Beaker
Spoon
Scale
Hot Plate
100 mL Graduated Cylinder
Procedure: Part A, Effect of Surface Area on Rate of Dissolving.
1. Place a beaker on the scale. Measure and record the mass of the beaker.
2. Pour some rock salt in the beaker. Measure the mass of the beaker and salt. Add or
remove the rock salt from the beaker if necessary until the mass of the beaker and salt is 5
to 10 grams more than the mass of the beaker alone. Record the mass of the beaker and
salt.
3. Repeat steps 2 and 3 with a second beaker and a sample of table salt. Be sure that the
mass of table salt in the beaker does not differ from the mass of the rock salt by more
than 0.1g.
4. Use a graduated cylinder to add 75 mL of room temperature water to each beaker. Not
the time. Observe the solutions for 2 minutes. After 2 minutes, look for any signs of
dissolving. Record your observations.
5. Place a glass stirring rod in each beaker. Note the time. Working with a partner, stir the
water gently in each beaker. Be sure to stir both samples at the same time and at the same
slow rate. Note the time when each sample completely dissolves. Record the time it took
for each salt sample to dissolve completely.
Procedure: Part B, The Effect of Temperature on solubility.
1. Put 50mL of room temperature water into a clean beaker. Use a thermometer to measure
the temperature of the water. Record this temperature in the data table. Remove the
thermometer from the beaker.
2. Add on spoonful of ammonium chloride to the water in the beaker. Stir vigorously with a
clean glass stirring rod until no more of the solid will dissolve. Make sure that you allow
enough time for the solid to dissolve.
3. Repeat step 2 until no more ammonium chloride will dissolve. Note the number of
spoonfuls of ammonium chloride that you added. Be sure to allow enough time for each
spoonful of ammonium chloride to dissolve before adding more. Record the number of
spoonfuls that dissolved in the data table.
4. Place the beaker of ammonium chloride solution on a hot plate. Place the thermometer in
the beaker. Turn the hot plate to the medium low setting and warm the solution to 40C.
5. Remove the thermometer from the beaker. Add more spoonfuls of ammonium chloride to
the beaker. Stir the solution and use the thermometer to check the temperature of the
solution after you add each spoonful. Note the total number of spoonfuls of ammonium
chloride that you added. Be sure to allow enough time for each spoonful of ammonium
chloride to dissolve before adding more. Use the heat setting of the hot plate to keep the
temperature constant as you add ammonium chloride to the beaker.
6. Record the total number of spoonfuls that have dissolved.
7. Turn up the hot plate to warm the solution to 60C. Then, repeat steps 11 and 12 with the
solution at this temperature.
8. Turn up the hot plate to warm the solution to 80C. Repeat steps 11 and 12 with the
solution at this temperature.
9. Record you data in the table.
Type if
NaCl
Approximate
Particle Size
(Larger /
Smaller)
Mass of
Beaker (g)
Mass of
Beaker and
Salt (g)
Appearance of
Mixture After 2
Minutes Without
Stirring
Time to Dissolve
(Seconds)
Rock Salt
Table Salt
Temperature (C)
18 – 24
40
60
80
Number of Spoonfuls of Ammonium Chloride Dissolved
Data Analysis
1. How did stirring affect the rate at which the salt dissolved?
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2. Why did the different salts dissolved at different rates?
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3. What is the manipulated variable in part A? In part B?
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4. In part B, why did the manipulated variable effect solubility?
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