Name:
Date:
Period:
Factors Affecting Solubility (50 pts)
Introduction:
The amount of a substance that will dissolve in a given amount of a solvent to give a solution
under specified conditions. Why is it that some soluble solids take so much longer to dissolve
than others? What factors affect the rate of dissolving? Understanding solutions is important
when studying chemistry since solutions are used to perform so many chemical reactions. In this
laboratory activity, you will test several factors and observe how each factor affects the rate of a
solute (what is being dissolved) dissolving in a solvent (what there is always more of and does
the dissolving of the other).
Materials (5pt): read through the lab and create your materials list (be sure to include quantities
needed)
Hypothesis (5pt):
In this lab, you will be examining how agitation or stirring, temperature, surface area, and
concentration affect the rate of solvation. How do you predict these four factors will affect the rate
of solvation? Answer in complete sentences.
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Procedure:
Available to you will be access to three different temperatures of water that the teacher will have
prepared in advance. At the supply table, you will find warm distilled water on a hotplate (warmed
to ~80oC, room temperature water, and chilled water at ~5oC)
Part A: Effect of Stirring on the Rate of Dissolving
1. Place two test tubes in a test tube rack. Label the tubes 1 and 2. Place about 0.2 g of salt
crystals in each test tube. The amount added is not as important as adding equal amount
to each tube.
2. Add enough room temperature water to fill each test tube about two-thirds full. Pour the
water carefully down the side of the tube so that little mixing occurs as the water is added.
3. Stopper test tube 2 and invert it. If all of the salt does not dissolve invert it again.
Continue inverting until all of the salt is dissolved. Count the number of inversions
required. One inversion consists of turning the stoppered test tube upside down, then
bringing it back right-side up.
4. Compare the rate of dissolving between the two tubes. Record your observations in Data
Table 1.
5. Rinse the contents of both test tubes down the drain. Rinse and dry each test tube.
Part B: Effect of Temperature on the Rate of Dissolving
1. Place three test tubes in a test tube rack. Label the tubes 1, 2, and 3. Add about 0.2 g of
salt crystals to each tube.
2. Measure the temperature of the water in the beakers from Steps 1, 2 and 3 with a
thermometer. Once they have reached the desired temperatures, record the temperatures
in Data Table 2 and proceed.
3. Fill the first test tube about two-thirds full with cold-ice-water. Pour the water carefully
down the side of the tube so that little mixing occurs as the water is added. Stopper the
tube and invert it to dissolve all of the salt. Count the number of inversions required.
Record your observations and the number of inversions required in Data Table 2.
4. Fill the second test tube about two-thirds full with room temperature water. Repeat
5. Fill the third test tube about two-thirds full with the hot water sample. Repeat
6. Rinse the contents of each test tube down the drain. Rinse and dry each test tube.
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Part C: Effect of Surface Area on the Rate of Dissolving
1. Place three test tubes in a test tube rack. Label the tubes 1, 2 and 3.
2. Obtain two of the larger rock salt crystals that are approximately the same mass. Weigh
them on a balance. Place one of the rock salt crystals into the first test tube.
3. Grind the second rock salt crystal with a mortar and pestle until it is a fine powder.
Transfer the powdered salt to the third test tube.
4. Add the same mass of salt crystals to the second test tube.
5. Fill the first test tube containing the rock salt crystal about two-thirds full with water.
6. Pour the water carefully down the side of the tube so that little mixing occurs as the water
is added. Stopper the tube and invert it to dissolve all of the salt. Count the number of
inversions.
7. If the number of inversions required to dissolve the crystal is greater than 25, stop and
record “25” for the number of inversions in Data Table 3.
8. Fill the second test tube containing the salt crystals about two-thirds full with water.
Repeat. Records your observations and the number of inversions required in Data Table
3.
9. Fill the third test tube containing the powdered salt two-thirds full with water. Repeat
Records your observations and the number of inversions required in Data Table 3.
10. Rinse the contents of each test tube down the drain. Rinse and dry each test tube.
Part D: Effect of Already Dissolved Solute on the Rate of Dissolving
11. Place two test tubes in a test tube rack. Label the tubes 1 and 2.
12. Place about 0.2 g of salt crystals in test tube 1. Fill this tube about two-thirds full with
water. Pour the water carefully down the side of the tube so that little mixing occurs as the
water is added. Stopper the tube and invert it to dissolve all of the salt. Count the number
of inversions required. Record your observations and the number of inversions required in
Data Table 4.
13. Add 0.4 g of salt crystals to test tube 2. Fill this tube about two-thirds full with water and
invert (without counting) until all of the salt is dissolved.
14. Now add about 0.2 g of additional salt crystals to test tube 2. Stopper test tube 2 and
invert until all of the salt is dissolved. Count the number of inversions required. Record
your observations and the number of inversions required in Data Table 4.
15. Rinse the contents of each test tube down the drain. Rinse and dry each tube.
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Name:
Date:
Period:
Factors Effecting Solubility Data Tables (10 pts)
Data Table 1: Effect of Stirring of the Rate of Dissolving
Observations
Uninverted
Number of Inversions
Test tube not inverted
Inverted
Data Table 2: Effect of Temperature on the Rate of Dissolving
Temp. (ºC) Observations
Number of Inversions
Cold
Room Temp.
Warm
Data Table 3: Effect of Surface Area on the Rate of Dissolving
Observations
Number of Inversions
Rock Salt
Salt Crystals
Powdered Salt
Data Table 4: Effect of Already Dissolved Solute on the Rate of Dissolving
Observations
Solution Containing
No Already
Dissolved Solute
Solution Containing
Already Dissolved
Solute
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Number of Inversions
Post-Lab Questions (30 pts) Answer in complete sentences
1. In this lab, what is the solute and what is the solvent?
2. What is the effect of inverting the test tube or stirring on the rate of dissolving? Explain.
3. What is the effect of temperature on the rate of dissolving? Explain.
4. What is the effect of surface area on the rate of dissolving? Explain.
5. Dissolving can be described as a surface phenomenon. Explain.
6. What is the effect of already dissolved solute or concentration on the rate of dissolving?
Explain.
7. How did your results compare to your hypothesis?
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8. The solubility of a given solute in a given solvent typically depends on temperature. For many
solids dissolved in liquid water, the solubility increases with temperature up to 100 °C. In liquid
water at high temperatures, the solubility of ionic solutes tends to decrease due to the change
of properties and structure of liquid water. The graph below shows solubility curves for some
typical solid inorganic salts.
a) Identify the three salts whose
solubility increases consistently
with temperature.
b) Identify the salt whose solubility
dramatically changes and at
what temperature.
c) Identify the salt whose solubility
decreases with temperature.
d) Does this information change your answer to question 3?
9. Below is a graph of the solubility curves of several gases. Discuss how gases solubility differs
from that of solids. Apply your understanding of kinetic molecular theory and the behavior of
gases to explain the gases solubility curves as temperature increases. (Hint: think about the
speed of which warm soda goes flat vs cold soda)
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