Law of Conservation of Mass - Experiment 3

The experiment will explore whether matter is created or destroyed during a chemical reaction.

Materials Substitutions
solutions of NaOH, CuSO4, NH4OH, and Na2CO3 solutions made with Drano, Bluestone algaecide, ammonia, and washing soda
4 graduated cylinders 4-2 oz plastic cups
3 150-mL beakers 3-5 oz plastic cups
balance

Procedure
1. Label the four graduated cylinders (or 2 oz cups) to contain the solutions (one each for NaOH, CuSO4, NH3 (aq), and Na2CO3).
2. Use a graduated cylinder to measure about 60 mL (2 oz) of the NaOH solution. Use a second graduated cylinder to measure about 60 mL (2 oz) of the CuSO4 solution and pour it into a 150-mL beaker (or 5 oz cup).
3. Carefully place the two solutions (in their containers) on the balance. Weigh the solutions and their containers together and record their combined weight.
4. Pour the NaOH solution into the container with the CuSO4 solution. Allow the solutions to mix. Describe what happens.
5. Weigh both containers and the mixture again. Record the new weight.
Did the weight change?
6. Repeat the process in steps # 2 and #3 above, first substituting NH3 (aq.) for the NaOH solution, then substituting Na2CO3 for the NaOH solution. In each case measure and record the masses as described in steps #3 and #5 above.

Data and Observations
1. Total weight of NaOH and CuSO4: Before __________g After _______g
2. Total weight of NH3 (aq) and CuSO4: Before __________g After _______g
3. Total weight of Na2CO3 and CuSO4: Before __________g After _______g
Complete the following equations:
4. NaOH + CuSO4 —–>_________________________________
5. NH3 (aq)+ CuSO4 ——->_____________________________
6. Na2CO3 + CuSO4 ——->____________________________

Extensions
The substances chosen for this lab are common and easy to find. You may want to repeat this lab with solutions of Fe(NO3)2 or Zn(NO3)2 solutions with Na2CO3. or NaOH. Note that NEITHER iron(II) or zinc carbonates or hydroxides are as insoluble as the copper(II) analog. While barium and lead salts have frequently been used in this type experiment, the problems associated with disposing of these materials suggests NOT USING either of these salts in experiments.

Questions
1. What is the insoluble solid that is produced? Use a solubility chart to predict the identity of the insoluble product.
2. Use the periodic table to prove that total formula mass is conserved. Why is it important to balance a chemical reaction?

Teacher’s Notes
This experiment verifies the Law of Conservation of Matter: Matter is neither created or destroyed as a result of chemical changes but may be changed in form. The balanced equations are as follows:
4. 2NaOH (aq) + CuSO4 (aq) —–> Na2SO4 (aq) + Cu(OH)2 (s)
5. 4NH3 (aq) + CuSO4 (aq) ——-> Cu(NH3)4SO4 (s)
6. Na2CO3 (aq) + CuSO4 (aq) ——-> Na2SO4 (aq) + CuCO3 (s)
The insoluble product that is formed is called a precipitate. Solubility Tables can help students predict which product will be insoluble (form a precipitate)
For additional ideas on this concept, see Experiment #2 and the Teacher’s Notes.

Solution Preparation
The sodium hydroxide can be obtained from Drano™ or Red Devil™ Lye. If you use Drano, the solution does not need to be very concentrated but you would want to filter the aluminum filings that are mixed in with the pellets of NaOH. Lye is CAUSTIC so wear gloves and wash all surfaces anyone might touch. Copper (II) sulfate can be purchased at a good hardware or swimming pool supply store as an algaecide (Bluestone) or root eater. Aqueous ammonia (formerly called ammonium hydroxide) is nothing more than household ammonia, and can be used straight out of the bottle from the grocery store. Finally, the sodium carbonate can be purchased at the grocery store as washing soda (Arm and Hammer) and can be mixed with water to form a solution.

0.1 M solutions can be prepared by dissolving the following masses of solid into enough water to make 1-L of solution:

Copper sulfate Sodium hydroxide Sodium carbonate
25g 4 g 10.6 g

Safety Precautions
As mentioned in the solutions preparations section, sodium hydroxide is CAUSTIC and should be handled carefully. Students should wear gloves. The base will feel slippery on the skin and should be washed immediately. Copper solutions can cause eye infections, so students should wash their hands after handling these substances, too.

Disposal
All solids should be placed in solid-waste containers. Most solutions can be poured down the sink. Check your local municipal water regulations concerning copper sulfate, as some water regulators restrict the concentration of copper (II) ions that can be poured down drains.