Fill each of your three test tubes about 1/4 full with baking soda, then add distilled water until the test tube is almost full, leaving some room for the cap. Cap each test tube and give it a good shake. Place one test tube in a coffee mug filled with ice water. Place the second test tube in a coffee mug filled with hot water. Leave the third tube sitting at room temperature. Let the test tubes sit for 10 minutes in order for the temperatures to equilibrate. There should be undissolved baking soda left in the bottom of each tube, indicating that the solutions are saturated. 

Step 2: titrate

After the 10 minutes, use your thermometer to measure the temperature of the liquid in the cold test tube and record it in your notebook. Be careful not to agitate the solution. The undissolved baking soda should remain at the bottom of the tube. Use one of your plastic pipettes to extract 3 mL of the saturated solution, being careful not to draw up any of the solid. Place the 3 mL of cold, saturated baking soda solution into a clean 100 mL beaker. Add distilled water to the beaker until the solution reaches the 20 mL mark. Optional: add 1-2 mL of your cabbage juice indicator and note your observations.

Pour about 50 mL of vinegar into a second clean beaker and label it. With a second pipette, draw up 0.5 mL (the first marking on the pipette) of vinegar. Add the 0.5 mL of vinegar to the beaker containing the baking soda solution. You should see some tiny bubbles, indicating that the neutralization reaction is taking place. Stir the solution until it stops producing bubbles. Continue adding vinegar 0.5 mL at a time, stirring between each addition until the bubbles stop. Keep track of how much vinegar you are adding (I used tally marks in my notebook). Stop adding vinegar once the equivalence point is reached. You can use the color of the cabbage juice and/or the absence of bubbling to indicate that the equivalence point has been reached. The bubbles can be a little sticky. Use your best judgment. 

Repeat step 2 for the room temperature and hot baking soda solutions. 

1) Calculate the molarity of acetic acid in vinegar, assuming it is 5% (m/v). 

2) For each of your three baking soda solutions (cold, room temperature, and hot), calculate the number of moles of acetic acid required to reach the equivalence point.

3) Calculate the molarity of sodium bicarbonate in each saturated baking soda solution. This is the molar solubility of baking soda at that temperature. 

4) Calculate K_sp for each of your three temperatures.