LAB 8
SOLID ZINC IN A SOLUTION OF LEAD ACETATE
BACKGROUND:
This lab is very similar to the last two labs you have completed. You will prepare a water solution of lead II acetate. You will also find the mass of a zinc strip and place it in the solution and observe what happens. At the end of the reaction you will remove the zinc strip and find its mass again.
Remember zinc is an element and lead II acetate is a compound. Lead II acetate is a hydrate, which means it has water molecules that are attached to it and this must be taken into account when finding its molecular weight. Lead II acetate has three water molecules attached and is written
lead II acetate .3 H2O.
obj. 1a,8,9 lab obj. 1-4
PROCEDURE
1. Obtain a piece of zinc, clean it with emery cloth and weigh it. Record this mass in your data table.
2. Mass a clean, empty 250 ml beaker. Record in data table.
3. Obtain approximately 2.00g of Lead II acetate trihydrate using the electronic balance. Record in data table. Lead II acetate trihydrate is poisonous so do not touch the crystals, if you do make sure to wash thoroughly.
4. Add the Lead II acetate trihydrate to the 250 ml beaker and dissolve it with 200 ml of distilled water. When this solution is made it will be cloudy, you can clear it by adding a few drops of concentrated acetic acid. This can be found at the front desk and must stay there. Be careful, concentrated acids are very dangerous.
5. Place the zinc strip into the solution and record your observations.
6. Cover the solution with a watch glass and set it in your drawer overnight.
NEXT DAY
7. Carefully open your drawer and remove the reaction beaker. Record your observations again.
8. Remove the watch glass. Shake off as many crystals as possible, I wonder what they could be? Remove as many crystals as possible by scraping the zinc with your plastic spoon.
9. You can enhance the drying of the zinc strip by dunking it in acetone which can be found at the front desk. When the strip is dry, weigh it and record in data table. Know wipe the zinc strip with paper towel and reweigh. If the mass is different you have wiped off more of the crystals, be sure to add this mass onto the mass of the dry crystals tomorrow.
10. Let the crystals settle and decant the solution into another beaker. There is no need to use filter paper since the crystals are dense enough that they will stay at the bottom of the beaker. The reason you pour into another beaker is that if some crystals do come out they won’t run down the drain.
11. Wash the crystals with about 10 ml of distilled water and again carefully decant. Wash the crystals and decant at least 3 more times.
12. Place the crystals in the drying oven to dry overnight.
NEXT DAY
13. Weigh the beaker with the crystals from the oven and record in data table. Dispose of the crystals as directed by your instructor.
CALCULATIONS
1. Calculate the change in mass of the zinc strip.
2. Calculate the mass of lead produced.
3. Find moles of zinc that reacted. Hint: watch sig figs.
4. Find moles of lead produced. Hint: watch sig figs.
5. Find the ratio: moles lead
moles zinc
your answer should be in decimal form and recorded to the correct number of sig figs.
6. Calculate and record the moles of Lead II acetate trihydrate used in the experiment. Again watch sig figs.
7. Find the ratio: moles lead
moles lead II acetate trihydrate
8. Use the results from steps 5 and 7 to write the simple whole number coefficients in the following:
1 mole zinc (solid) + __ mole(s) Lead II acetate trihydrate (sol’n) -->
___ mole(s) lead (solid) + ___ mole(s) zinc acetate (solution)
9. How many atoms of zinc were involved in this experiment? (Hint: use the # of grams that were “lost”)
10. How many atoms of lead were involved in this experiment? (Hint: use the # of grams that were“made”)