Question

1. Solubility in WATER

Check solubility of four solutes in water (H₂O). For each solute record how many teaspoons dissolved in 1/2 cup of water.

NaCl: Start out with 4 small glasses (cups) and add 1/2 cup of water to each. Put 1/2 level teaspoon (tsp) of salt (NaCl) into the first cup and stir. If it dissolves within 1 minute; add another 1/2 tsp of salt and stir. Count the number of 1/2 tsps you are adding. Repeat until no more dissolves.

Record the number of teaspoons of salt (NaCl) that dissolved in 1/2 cup water.

Sugar: Put 1/2 level tsp of sugar (C₁₂H₂₂O₁₁) into the second cup and stir. Keep adding sugar 1/2 tsp at a time until no more dissolves.

Record the number of teaspoons of sugar that dissolved in 1/2 cup water.

Alcohol: Put 1/2 level tsp of rubbing alcohol (C₃H₈O) into the third cup and stir. Keep adding alsohol 1/2 tsp at a time until no more dissolves.

Record the number of teaspoons of alcohol that dissolved in 1/2 cup water.

Margarine: Put 1/2 level tsp of melted margarine (C₂₇H₅₆) into the fourth cup and stir. Keep adding the melted margarine 1/2 tsp at a time until no more dissolves.

Record the number of teaspoons of margarine that dissolved in 1/2 cup water.

Which solute was most soluble in water? Which solute was least soluble in water? What about that compound do you think made it more soluble in water?

2. Solubility in Oil.

Check solubility of four solutes in oil (C₁₇H₂₆). For each solute record how many teaspoons dissolved in 1/2 cup of oil.

Salt: Start out with 4 small glasses (cups) and add 1/2 cup cooking oil to each. Take the first cup and add salt (NaCl) 1/2 teaspoon at a time, just as you did in (1) above until no more dissolves.

Record the number of teaspoons of salt that dissolved in 1/2 cup oil.

Sugar: Take the second cup and add sugar (C₁₂H₂₂O₁₁) 1/2 tsp at a time, just as you did in (1) above until no more dissolves.

Record the number of teaspoons of sugar that dissolved in 1/2 cup oil.

Alcohol: Take the third cup and add alcohol (C₃H₈O) 1/2 tsp at a time, just as you did in (1) above until no more dissolves.

Record the number of teaspoons of alcohol that dissolved in 1/2 cup oil.

Margarine: Take the fourth cup and add melted margarine (C₂₇H₅₆) 1/2 tsp at a time, just as you did in (1) above until no more dissolves.

Record the number of teaspoons of margarine that dissolved in 1/2 cup oil.

Which solute was most soluble in oil? Which solute was least soluble in oil? What about that compound do you think made it more soluble in oil?

3. The effect of heating on solubility:

Boil some water and put 1/2 cup into a measuring cup. Add sugar 1/2 tsp at a time until no more will dissolve.

Record the number of teaspoons of sugar that dissolved in 1/2 cup HOT water.

Compare this solubility in hot water to the solubility you got for sugar in water at room temperature. Did the solubility of sugar in water increase or decrease with increasing temperature?

Open a cold can of soda pop from the refrigerator and pour it into two glasses. The bubbles you see are CO₂ gas molecules dissolved in water. Leave one soda pop sitting on the counter at room temperature and place one back into your refrigerator. Come back in an hour and check them. Compare the bubbles in the warm soda to those of the cold soda? Does this mean that the solubility of CO₂ gas increased or decreased with increasing temperature?

Did the solubility of the solid sugar and the gaseous carbon dioxide respond to temperature change in the same way? Explain.

4. One of your solutes was an ionic compound.

a. Which solute was ionic.
b. Which solvent was it most soluble in?
c. What kind of attractive forces are responsible for the solubility? (see list sections 6.3 and 6.4).

There is a rule that says “Like dissolves Like”. This means that non polar (usually pure carbon-hydrogen compounds) solvents dissolve non polar solutes best. This means that polar solvents like water dissolve polar solutes best. Based on their solubilities, indicate whether the following solutes are more likely to consist of polar or nonpolar molecules.

(a) Sugar (b) Alcohol (c) Margarine.

Which solute was most soluble in cooking oil. What kind of electrical attraction exists between solute and solvent particles that accounts for this solubility? (hint: it is one of the forces from 6.3 and 6.4).

Calculate the percent by mass of NaCl in the solution that you prepared in (1). Assume 1 tsp of NaCl has a mass of 2.4 grams and that 1 cup of water has a mass of 235 grams. Show your work or explain how you got that answer. Refer back to chapter 5 for % mass calculations.

Answer 1