Hr.: ____ Mass-Mass Relationships in Reactions Name: _______________________________________________ Unit 8 – Moles Lab 2 Pre-lab Discussion As you have learned, given a balanced chemical equation and the mass of one of the substances in the reaction, the mass of any other substances in the reaction can be calculated. Calculations in which a known mass is used to find an unknown mass in a chemical reaction are called mass-mass stoichiometry calculations. In this experiment, a double replacement reaction will occur when an aqueous solution of sodium carbonate is mixed with an aqueous solution of zinc sulfate. There are two products of this reaction. One is the insoluble solid (zinc carbonate), which will precipitate out of solution. The other is a soluble salt (sodium sulfate) which will remain in solution. The insoluble salt will be separated from the liquid and its mass will be determined. The value of the experimentally measured mass of the compound will be compared with the theoretical mass of the compound predicted by mass-mass stoichiometry calculations. This experiment will emphasize the importance of mass-mass stoichiometry calculations in the chemistry laboratory and percent yield. Purpose To compare the theoretical mass of one of the products of a double replacement reaction with the experimentally determined mass of the same product. Equipment Materials Graduated cylinder 3 -- Beakers Stirring rod Ring stand Iron ring Funnel Sodium carbonate [Na2CO3] Zinc sulfate [ZnSO4] Filter paper Safety Handle glassware with care to avoid breakage. Always wear safety glasses when working in the lab. Procedure 1. Using the balance, measure out exactly 1.1 g of zinc sulfate. Record this mass as (a) in your list of data. 2. Place the ZnSO4 in a clean beaker and add 25 mL of water. Stir thoroughly to make sure all crystals are dissolved. Rinse off the stirring rod. 3. Measure out approximately 1.4 g of sodium carbonate. Place it in a separate clean beaker and add 25 mL of water. Stir until all of the crystals are dissolved. 4. Pour the Na2CO3 solution into the beaker containing the solution of ZnSO4. Stir. Record your observations as (d) in your list of data. 5. Fold a piece of filter paper and place it in the funnel. 6. SLOWLY pour the mixture from the beaker into the funnel. As shown by your teacher and below in the picture. 7. Rinse the beaker with about 10 mL of water. Pour the rinse water through the filter. Repeat the rinsing and filtering until all the precipitate is out of the beaker. 8. Find the mass of a clean, dry evaporating dish. Record this mass as (b) in your list of data. 9. Remove the filter paper and precipitate from the funnel. Scrape as much of the precipitate into the evaporating dish as possible. 10. Spread the precipitate out over the bottom of the evaporating dish and heat it on a bunsen burner or hot plate. Use a high setting to boil off the water. 11. Once the water has boiled off remove the dish and allow it to cool for a few minutes. 12. When the dish is cool enough to touch, find the mass of the dish +precipitate. Record this as mass (c) in your list of data. Data and Observations a. Mass of ZnSO4 a. ___________________________________ b. Mass of evaporating dish b. ___________________________________ c. Mass of evaporating dish + precipitate ZnCO3 c. ___________________________________ d. Observations Calculations 1. You performed a double replacement reaction where sodium carbonate reacted with zinc sulfate. Write a balanced equation for this reaction. Be sure to include states of matter and indicate which product is the solid. 2. Using stoichiometry, calculate the number of grams of ZnCO3 that you should have produced if you started with 1.1 g ZnSO4 and it reacted completely. 3. Find the experimental mass of ZnCO3 formed : c–b 4. Find your percent yield |𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 − 𝑎𝑐𝑡𝑢𝑎𝑙| %𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑦𝑖𝑒𝑙𝑑 = × 100 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 Conclusions and Questions 1. Use the balanced equation for the reaction to find the following mole ratios. 𝑁𝑎2 𝑆𝑂4 a. 𝑍𝑛𝑆𝑂4 b. 𝑁𝑎2 𝐶𝑂3 𝑍𝑛𝐶𝑂3 2. In your own words, give a brief explanation of a double replacement reaction. What must one of the products be? 3. Suggest at least 3 possible sources of error in this experiment. Be specific. 4. Define the terms filtrate and precipitate. 5. In the chemical reaction CaCO3 CaO + CO2 , if 40.0 g of CaCO3 is decomposed: a. How many grams of CaO is produced? b. How many grams of CO2 is produced?