Science 102 Laboratory Investigation

Title: Hey, Something's Missing!

Background: A balanced equation contains much information. For example, it shows you what chemicals are necessary to start a particular reaction (reactants) and what chemicals are created when the reaction is finished (the products.) A balanced equation can also be used to show that the mass of all the reactants equals the mass of all the products. This idea is called Conservation of Mass. But, sometime, it seems that something is wrong because the initial and final masses are different. What is happening in these situations?

Process:

1. Just rinse a medium size test tube but rinse and dry a 100 ml beaker. Place the beaker on the balance pan and add about 10 g of baking soda to it. Then, set the beaker aside.

2. Rinse a graduated cylinder and then use it to measure out 15 ml of vinegar. Pour the vinegar into the test tube. Be sure the bottom of the test tube is dry.

3. Place the beaker and its baking soda back on the pan of the balance and then set the test tube and its vinegar in the beaker and baking soda. No mixing yet.

4. Record the total mass of the glassware and chemicals.

5. Now, move the glassware from the balance pan, take out the test tube and pour the vinegar into the baking soda. Use a wooden splint to carefully mix the baking soda and vinegar. After the reaction stops, place the empty test tube back into the beaker and place them both back onto the balance pan.
Reweigh the glassware and chemicals and record the mass.

6. Now, carefully dispose of the chemicals as directed. Clean up the glassware and your work station and wash your paws.

Questions:

1. What is the evidence of a chemical reaction?

2. According to the idea of Conservation of Mass, how should the initial and final mass values compare?

3. How do your initial and final values compare?

4. Would you say mass has been "conserved" during this reaction?

5. Can you explain your two mass readings?