**Double replacement lab 2

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STOICHIOMETRY
OF A
DOUBLE REPLACEMENT REACTION

INTRODUCTION:

There are two types of chemical analysis; qualitative analysis which is the identification of a substance present in a material, and quanitative analysis which measures the amount of the substance. In this lab, you will perform a quantitative analysis of a two-step reaction. Copper(II) oxide will be synthesized from a known mass of copper(II) sulfate pentahydrate. Using the relationship of the balanced equation, and other stoichiometry relationships, you will calculate a theoretical yield of CuO, and your actual yield. You then will calculate a percent yield.

Copper(II) sulfate pentahydrate will be dissolved in water and reacted using a double replacement reaction with sodium hydroxide. The addition of hydroxide ions to a solution containing copper(II) ions results in the precipitation of copper(II) hydroxide. Subsequent heating of the copper(II) hydroxide results in decomposition to copper(II) oxide and water. The CuO can be quantitatively filtered, dried and weighed.

You will perform the reaction with an accurately weighed amount of CuSO₄+5H₂O. From this amount, you will calculate the amount of copper(II) oxide that should be formed (theoretical yield). By performing the experiment, the experimental yield is obtained and this value is compared with the theoretical yield. The ratio of the experimental to the theoretical (times 100%) is the percent yield.

MATERIALS NEEDED:
Safety goggles		100-ml beaker
Ring stand
Small iron ring		Balance
Large iron ring with wire gauze		Weighing dish
Bunsen burner		Drying oven or light
		10-ml graduated cylinder
Filtering funnel
#1 filter paper		1.8 to 2.2 grams CuSO45H2O
250-ml beaker		2.5g NaOH dissolved in 10 ml H2O

PROCEDURE:

1. Weigh between 1.8 and 2.2 grams of copper(II) sulfate pentahydrate in a weighing dish, to the nearest 0.01 gram. Be sure to use proper procedure for the balance used. Record the mass of the copper(II) pentahydrate on your DATA TABLE.

2. Transfer the chemical to your 250-ml beaker. Add 10 ml of distilled water to the beaker. Remember, use some of the water to rinse any chemical that remains on the weighing dish. This is quantitative so you need to make sure everything gets transferred. Swirl the beaker to dissolve the solid.

3. Add 2.5g of NaOH to10 ml of water and add solution to the beaker, and carefully swirl to mix. REMEMBER: NaOH is very caustic, and will burn your skin.

4. Set up the ring stand and wire gauze. Place the beaker on the wire gauze. Heat the mixture to the boiling point. Try to avoid spattering. If spattering occurs use a wash bottle to wash all the solid back down into the solution. Heat until all the blue solid has been decomposed to copper(II) oxide and water (a few minutes). Allow the mixture to cool before filtering.

5. Fold a piece of #1 filter paper in half, then in fourths.

6. Place the filter paper in the 100-ml beaker. If more than one person or group is conducting this experiment, mark your 100-ml beaker, with a pencil only, on the white square. Find the mass of the 100-ml beaker and filter paper to the nearest 0.01 g and record on your data table.

7. Open the cone with one thickness on one side, and three thicknesses on the other. Set-up a filtering funnel on the ring stand and small ring. Place the 100-ml beaker that you massed, under the funnel. While holding the filter paper in place, wet the paper with water. This will seal it to the funnel.

8. Now transfer the previously heated mixture to the filter. Be careful to never allow the filter paper to be filled more than about 0.5 cm from the top of the paper. Be patient and add small amounts. when all the liquid has been transferred to the funnel, use a small amount of water, and wash all the solid precipitate into the filter paper.

9. When all the liquid has filtered through the filter paper, wash the precipitate, to remove any remaining sodium sulfate or sodium hydroxide. Do 3 small rinses.

10. Discard the contents of the 100-ml beaker, and rinse it thoroughly with 4 or 5 rinses of distilled water. Now carefully remove the filter paper containing the copper(II) oxide precipitate, and place it into the 100-ml beaker.

11. Place the beaker with the filter paper and precipitate in the drying oven at 105 ^oC. Allow to dry for 24 hours.

12. After 24 hours. Remove the beaker containing the filter paper and precipitate from the drying oven and allow to cool.

13. When cool, find the mass of the beaker, filter paper, and precipitate to the nearest 0.01 g, and record in your DATA TABLE.

DATA TABLE:

Formula weight of CuSO₄5 H₂O = ____________

Formula weight of CuO = ____________

Mass of CuSO₄5 H₂O = __________ g

Mass of 100-ml beaker and filter paper = __________ g

Mass of 100-ml beaker, filter paper, and CuO precipitate = __________ g

CALCULATIONS:

15. Calculate the theoretical yield of CuO based on both the copper II sulfate and the sodium hydroxide. Determine the limiting reactant and the theoretical yield.

Theoretical yield of CuO = _________ g

16. Calculate the mass of CuO you obtained in the experiment (experimental yield).

Experimental yield of CuO = _________ g

17. Now calculate the percent yield of CuO.

Percent yield of CuO = _________ %