Experiment 1: Experiment 1: Determining the Chemical Formula for Copper Gluconat

Question

Experiment 1: Experiment 1: Determining the Chemical Formula for Copper Gluconate
The experiments in this lab use a compound named copper gluconate (C12H22CuO14). Copper gluconate has a variety of uses and applications. For example, copper gluconate is used as a primary ingredient in the breath mint Certs®. It is also used as a source of copper in nutritional supplements. Your task will be to determine the chemical formula of the compound by isolating the copper and determining the molar ratio of copper and gluconate in the compound.

Materials:

1 g Copper gluconate
10 mL 0.5% Salt, NaCl
10 mL Graduated cylinder
Scale
(1) 50 mL Beaker
250 mL Glass beaker
2 Aluminum washers
Sterno®
Metal forceps
Ring stand

Ring for the ring stand
Stir rod
Matches
Cupcake wrapper
*Oven
*Hot pad or towel
*Baking pan
*20 mL Distilled Water

Procedure:
1. Put the 250 mL beaker on the scale and tare the scale.
2. Measure 1.0 g of the copper gluconate in the beaker on the scale. Record the exact mass in the Data section near the end of the procedure.
3. Use the graduated cylinder to measure and pour 10 mL 0.5% NaCl into the beaker with the copper gluconate. You may need to gently swirl the solution if all the copper gluconate does not immediately suspend into the solution.
4. Add two aluminum washers to the solution.
5. Fasten the ring approximately 6 - 10 inches up on the ring stand and place the beaker on the ring.

6. Place the Sterno® directly beneath the beaker. Remove the inner cap on the Sterno® and ignite the inner contents with the matches. Heat the beaker until solution clears. Your solution may not turn completely clear, but some color change should be evident. Alternatively you can also determine when the reaction is complete by looking for the formation of gas bubbles on the surface of the washers. When the formed gas bubbles are gone, then the reaction is complete.
Note: Carefully monitor the set-up while the Sterno® is in use. You may need to adjust the height of the ring/beaker to ensure that the beaker is heated enough; and, to avoid exposing the beaker from high heat.
**Carefully observe the set-up you choose!! Do not leave the beaker unattended
while exposed to the Sterno®. Plastic beakers should never be used with heat.**
7. Carefully remove the beaker from heat, and use forceps to replace the lid on the Sterno®. Decant (pour) the clear liquid into a 50 mL beaker.
8. When all that remains in the original beaker are the copper plated washers, rinse the washers with distilled water and decant the remaining liquid, being careful not to lose any copper, into a container. This water can be disposed of down a sink drain. Repeat this process three times.
9. Remove the first washer and use the stir stick to scrape the copper into the metal cupcake wrapper.
10. Rinse the washer with distilled water to be sure all copper is recovered into the wrapper.
11. Repeat the process for the second washer, scraping the copper into the same wrapper.
12. Place the wrapper on a baking pan and put it in the oven at 115 °C (239 °F) to dry the product. Monitor the wrapper and contents and use a hot pad or towel to carefully remove them from the oven after 45 minutes, or after all of the water has evaporated.
13. After the wrapper has cooled to room temperature, empty the dried copper from the wrapper onto the scale and weigh the final mass. Record the mass in the Data section below.

Data:
Mass of copper gluconate (initial, see Step 2): _____________________
Mass of copper (final; see Step 13): _____________________
Calculations
Mass of copper recovered:________________
Moles of copper :________________

Mass of gluconate:_______________
Moles of gluconate:________________
Chemical formula:_________________

Questions to be answered:

Question 1. Using your own lab results, show your calculations for your moles of copper produced. You must show all work to receive credit.

Question 2. Using your own lab results, show your calculations for your moles of gluconate. You must show all work to receive credit.

Question 3. Using your own lab results, determine the chemical formula of copper glutonate. You must show all work.

Question 4. List two sources of error in the experiment and explain the impact they had on the results.

Question 5. Using your own lab results, calculate the percent composition for each element in the compound copper gluconate. Clearly label each element and the percentage. You must show all work (not just the formula) to receive credit.

Explanation / Answer

When copper gluconate reacts with sodium chloride, sodium gluconate and copper chloride are formed and both are dissolved in water.

Cu(C12H22O14) + 2NaCl --> 2Na+ (aq) + 2C6H11O7- (aq)+ Cu2+ (aq)+ 2Cl- (aq)

1:

Initial weight of copper gluconate = 1 g

Molecular weight of copper gluconate = 453.8 gmol-1  

atomic ass of copper = 63.5 g mol-1

453.8 g of copper gluconate that contains the mass of copper = 63.5 g

Hence 1 g of copper gluconate that will contain the mass of copper

= (63.5 g Cu / 453.8 g copper gluconate) x (1 g copper gluconate)

= 0.140 g Cu

Hence mass of copper recovered will be around 0.140 g

There fore moles of Cu produced = 0.140 g / 63.5 g mol-1 = 0.00220 mol

2: Weight of gluconate produced = 1 g - 0.140g = 0.86 g

molecular mass of gluconate ion = 195 gmol-1

Hence moles of gluconate = 0.86 / 195 = 0.0044 mol

3: molar ration of Copper and gluconate ion = 0.0022 : 0.0044 = 1:2

Hence 1 mol of copper gluconate contains 1 mol copper atom and 2 mole gluconate ion.

Hence chemical formulae of copper gluconate is Cu(C6H11O7)2 or C12H22O14Cu

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