Experiment B1: Solutions

Prerequisite Skills
No prerequisite skills have been assigned to this laboratory.

Objectives
When you have completed the following experiment, you will have

1. learned of the different factors involved in the solution process.
2. learned of the different factors affecting solubility.
3. seen illustrated some of the colligative properties of solutions.
4. determined the conductivity of various common electrolytic and non-electrolytic solutions.

Safety Tips
Experiment Location. Work on a steady table in a safe secure place. Keep doors and windows closed to prevent drafts. Your kitchen stove will be used as a heat source. Do no cooking while the experiment is in progress.
Handling of Chemicals. All are common household chemicals, but should be treated with care.
Safety glasses should be worn at all times. Wear appropriate clothes and closed-toed shoes.

Procedure

A. Solubility
1. Dissolution vs. Particle Size Dissolution
Fill one small test tube to a depth of about 0.3 cm with table salt and fill the other to a depth of 0.3 cm with rock salt. Now add about 8 mL (1/2 tbsp) of cold tap water to each.
Cover both tubes with a thumb and shake.
Note the time it takes to dissolve the salt in each tube.

2. Dissolution vs. Stirring
Fill two small test tubes to 0.3 cm depth with table salt and add about 8 mL of cold tap water to each.
Set one tube aside and shake the other one covering the mouth of the test tube with your thumb.
Note the time it takes to dissolve the salt in each tube.

3. Dissolution vs. Temperature
Measure out two salt samples, each 1/8 of a teaspoon.
Fill one small test tube with 8 mL of cold tap water and the other tube with 8 mL of hot tap water.
Cover the mouth of both tubes with a thumb and then shake. Note the time it takes to dissolve the salt in each tube.

4. Dissolution vs. Diffusion
Take two to three crystal chunks of instant coffee and wrap in a small piece of paper towel.
Place this packet at the bottom of one of the large test tubes and fill with cold tap water.
Add cold tap water to a second large test tube.
Prepare a second coffee packet and carefully place this packet on top of the water, making sure it is completely submerged in the water.
Set both tubes aside in an upright position. Leave these test tubes undisturbed for at least two hours, checking occasionally on the progress of both tubes.
You may need to carefully lift both tubes up and hold them against a white sheet of paper to notice any results.
Record your observations.

B. Saturation

1. Saturated Solution
Fill a 150 mL beaker one-third (~50 mL) full of cold tap water, and add sugar slowly while stirring.
Keep adding sugar until no more sugar dissolves. (Be patient—it takes a lot of sugar!)
You will know that the solution is saturated when a few crystals of sugar remain at the bottom of the beaker.

2. Increased Temperature
Fill a small pot about one-quarter full of hot tap water and put on low heat on a stove or heating surface.
CAUTION: Do not touch the hot pot or the hot water.
You may get burned! Place the beaker with sugar water (from step 1 above) into the hot water, making sure it will not tip over.
Warm the sugar solution gently while stirring. Note what happens to the sugar crystals at the bottom of the beaker.
Now continue to add more sugar so that you have a saturated solution (again—be patient!)
This time make sure there are no extra crystals of sugar at the bottom of the beaker at your saturation endpoint.
The easiest way to accomplish this is to follow the same procedure as in step 1 and then add a little water to dissolve the last few crystals.
Save this solution and keep it warm, you will need it for later.

3. Evaporation
Pour half of your solution from step 2 into a 50 mL beaker and place in the oven at 175°C (350 degrees F).
Allow about half the water in this 50 mL beaker to evaporate by boiling.
(Don’t forget about it!) Take the beaker out of the oven and allow it to cool.
Record your results.
While waiting continue on with step 4.

4. Supersaturation
Remove the other half of the warm sugar solution from step 2 and allow it to cool undisturbed.
The sugar should remain in solution and upon cooling will form a supersatured solution.
The excess sugar can be brought out of solution by “seeding” the solution with a crystal of sugar.
Tie a coarse string (frayed a little is OK) to the center of a pencil. Dip the end of the thread in some corn syrup and stick a few sugar crystals to the thread.
Lower the thread and sugar gently into the saturated solution and support the thread by laying the pencil across the mouth of the beaker.
You can adjust the height of the suspended thread by rotating the pencil in the appropriate direction and winding the thread in and out.
Allow this setup to sit undisturbed for a few days.
After a few days you should have some nice rock candy.
Record your observations. CAUTION: Do not eat the rock candy formed in this experiment!

Experiment B1: Solutions Prerequisite Skills No prerequisite sk...