Water as a Solvent
LA
O
RY
59
T
BO RA
J
ust like climate, ocean currents are affected by many factors. These
factors include wind, water temperature, the shape of the ocean
floor, and the rotation of the earth itself. The salinity (suh-LIN-ihtee) of seawater is another factor driving ocean currents. Salinity is the
amount of salt dissolved in water. In this activity, you will investigate
how well solids dissolve in water compared to other liquids.
CHALLENGE
How well do different liquids dissolve the same solid?
In the Middle East, the Dead Sea is so salty that you can see areas of dried salt as well as water.
E-49
Activity 59 • Water as a Solvent
MATERIALS
For each group of four students
1
container of sodium chloride
1
container of calcium chloride
1
30-mL dropper bottle of water
1
60-mL dropper bottle of ethanol
1
60-mL dropper bottle of mineral oil
1
cup of water
For each pair of students
1
SEPUP tray
1
stir stick
For each student
1
pair of safety goggles
SAFET Y NOTE
Wear safety eyewear, and do not touch the chemicals directly.
Follow all classroom safety rules. Wash your hands when you finish
the activity.
PROCEDURE
1. Carefully read the table below to review the different liquids and
solids you will investigate in this activity.
Mixing Liquids and Solids
Cup
E-50
Liquid
Solid
1
15 drops of water
2 level scoops of sodium chloride
2
15 drops of ethanol
2 level scoops of sodium chloride
3
15 drops of mineral oil
2 level scoops of sodium chloride
4
None
2 level scoops of sodium chloride
5
15 drops of water
2 level scoops of calcium chloride
6
15 drops of ethanol
2 level scoops of calcium chloride
7
15 drops of mineral oil
2 level scoops of calcium chloride
8
None
2 level scoops of calcium chloride
Water as a Solvent • Activity 59
2. Create a data table to record (a) your observations of the liquids in
Cups 1–8 (b) your observations of each liquid and solid mixed
together and (c) the amount of solid dissolved in each liquid.
3. Work with your partner and use Table 1 to add the correct amounts
of three different liquids to Cups 1–3 of your SEPUP tray.
4. Observe the color, transparency, and odor of each liquid, and
record your observations of Cups 1–3 in your data table.
5. Use the scoop end of your stir stick, as
shown, to add 2 level scoops of sodium
chloride to Cups 1–4.
6. Stir the mixture in each cup for exactly
one minute, making sure to rinse the
stir stick before placing it in the next cup.
7. Compare the amount of solid remaining in the cup to the amount
of solid in Cup 4. Estimate the amount of solid that dissolved (all,
some, or none), and record your observations in your table.
8. Use Cups 5–8 to repeat Steps 3–7, but when you come to Step 5, use
calcium chloride instead of sodium chloride.
ANALYSIS
1. A liquid that has a solid dissolved in it is called a solvent (SOLvent). In this investigation:
a. what are the solvents?
b. in which solvent did the solids dissolve the most?
2. All water on earth contains some dissolved materials, usually salts.
Ocean water is about 3.5% salt, with sodium chloride (table salt)
being the most common dissolved salt. Calcium chloride is also
found on the earth’s surface. Would you expect to find calcium
chloride in ocean water? Explain.
3. Water is sometimes called the universal solvent. Explain what you
think this statement means. Support your answer with evidence
from this activity.
4. Do you think most of the water on the earth is salt water or freshwater? Why?
E-51
Activity 59 • Water as a Solvent
EXTENSION
How good a solvent is water? Design an experiment to find out. Consider investigating how much of a particular solid can dissolve in
water or test other solids to see if they dissolve in water. Then present
your results to the class.
E-52