CHEMISTRY – STOICHIOMETRY – LIMITING AND EXCESS ...



CHEMISTRY – STOICHIOMETRY – LIMITING REAGENT /PERCENTAGE YIELD LAB

Purpose : To determine the limiting reagent and the percentage yield for a double replacement reaction between Copper (II) Chloride and Sodium Carbonate .

BACKGROUND : In this lab/exam you will be performing a double replacement reaction in which one of the products will form a solid precipitate. The Copper (II) Carbonate will form a milk cloudy solid in the beaker or flask. You will be using equal amounts of the reactants in this lab and you will be able to determine the stochiometric relationship between the reactants and products. You will filter out the Copper (II) Carbonate precipitate and dry it on a hotplate and calculate the mass of this product.

Write the complete balanced equation for this lab

(double replacement reaction of copper (II) chloride and sodium carbonate)

Materials:

2 Erlenmeyer Flasks 1 electronic balance Cupric Chloride 2 Stirring Rods

1 piece fast filter paper 1 medium sized funnel Sodium Carbonate Wash Bottle

Pre Lab Questions: Write answers in your own words in complete sentences.

1. What is a limiting reactant? ___________________________________________________________

_____________________________________________________________________________________

2. What is an excess reactant? ____________________________________________________________

_____________________________________________________________________________________

3. The theoretical yield comes from the __________________________ reactant.

4. The maximum amount of product that can be formed is known as the _________________ _________.

5. A chemist makes 50mL of a 0.15M CuCl2 solution and 50mL of a 0.15M Na2CO3 solution.

a. How many grams of the copper (II) chloride were used?

b. How many grams of sodium carbonate were used?

6. The chemist then mixes the two solutions together. A double replacement reaction takes place and the products are Copper (II) carbonate and Sodium chloride. He filters out the CuCO3 and masses it. He finds that he has made 0.75 grams of Copper (II) Carbonate.

Show your work for all of the following calculations

a. What was the limiting reactant? __________________

b. What is the theoretical yield? _______________

c. What is the percentage yield? __________________________________

Procedure

1. Obtain two clean Erlenmeyer flasks, if they are dirty make sure to clean them.

2. Make 50mL of a 0.15 M solution of CuCl2 and a 50mL 0.15 M Na2CO3 solution. Each in their own Erlenmeyer flask.

3. Observe the color of the reactants and record in Data Table.

4. Now slowly add some of the CuCl2 to the Na2CO3 flask a little at a time, swirling the mixture with each addition of Copper (II) Chloride. The swirling causes the ions to collide into one another allowing for more product to be created. When flask is empty, rinse with a small amount of water from the wash bottle and pour into the other flask.

5. Weigh and record the mass of a dry piece of filter paper in Data Table. Fold the paper in four to create a cone (taco, snow cone and then three layers on one side and one on the other). With pencil, write your initials, lab partner’s initials and period on OUTSIDE of filter. Do not use a felt tip marker.

6. Set up the filtering apparatus by placing the filter in the funnel; the funnel into the neck of an empty flask, and then wetting the paper with a small amount of distilled water to make it sticks to the funnel. Make sure there are no gaps between the paper and the funnel.

7. Slowly pour your final mixture through the filtering apparatus a little at a time. Take care to not over fill the funnel as it could tip over or the fluid may run over the filter and into the flask. When the flask is empty, add a small amount of distilled water and swirl around flask. Pour this into the filter paper as well. The filtrate should be clear in the bottom of the flask. If is not clear, record and re-filter the filtrate.

8. Place filter paper and precipitate on a watch glass and let dry overnight.

9. Weigh the filter paper and record the mass and color of the CuCO3 in the Data Table.

10. Clean up your mess and rinse all equipment completely. If any material is stuck in flasks, use a brush to completely clean out flask. Do not use detergent and do not attempt to dry flasks with towel. Put all the equipment back where it belongs.

DATA TABLE

|Moles of Na2CO3 |Mass of Na2CO3 |

| | |

| | |

|Moles of CuCl2 |Mass of CuCl2 |

| | |

|Mass of filter paper and CuCO3 |Mass of filter paper |

| | |

|Color of CuCl2 |Mass of CuCO3 |

| | |

|Color of Na2CO3 |Moles of CuCO3 |

| | |

|Color of CuCO3 |Actual yield of CuCO3 in grams |

| | |

|Limiting Reagent |Theoretical Yield of CuCO3 in grams |

| | |

|Excess Reagent |Percentage yield of CuCO3 |

| | |

|Filtrate Color |Did you re-filter? |

| | |

Calculations. Show all work, answers must be reported in DATA TABLE.

If NO WORK, NO CREDIT. IF NOT LEGIBLE and IN ORDER, NO CREDIT.

1. Calculate the number of moles CuCl2 necessary to make 50mL of a 0.15M solution.

2. Calculate the number of moles Na2CO3 necessary to make 50mL of a 0.15M solution.

3. Molar mass of CuCl2, Na2CO3 and CuCO3. Correct units must be shown.

4. Calculate the mass of CuCl2 and Na2CO3 necessary to make 50mL of a 0.15M solution of each.

5. Write a balanced equation, states included, for this reaction.

6. Calculate the mass of CuCO3 produced. This is your actual yield.

7. Calculate the moles of CuCO3 produced.

8. Calculate the theoretical yield using the amounts of reactants from Data Table. Record limiting and excess reactant in Data Table.

9. Calculate percentage yield.

10. Was your percentage yield 100 %, why or why not?

11. According to your calculations which reactant caused the reaction to stop and why?

12. Why did we dry the filter paper over night? How would wet filter paper affect your percentage yield?

13. What is the difference between actual and theoretical yield (not a number, a written answer)?

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