Copper & Aluminum in Water Lab Answers

Purpose:

The purpose of the lab was to dissolve Copper salt in water with an excess of Aluminum. The mass of the Copper formed was to be determined and the percentage yield was to be calculated.

Related theory

A chemical reaction is the change of substance into a new one that has a different chemical identity. It is usually followed by easily observes physical effects such as the emission of heat and light, the formation of a precipitate, the evolution of gas, a colour change etc.

An actual yield is the products that are formed under actual conditions. The actual yield divided by the theoretical yield gives you the percentage yield. A theoretical yield of a reaction is the amount of product that would be formed if the reaction went to completion.

Procedure

• A mass of 2.00g of Copper (11) dihydrate salt to 0.01 g was dissolved in 50.0ml of water in a beaker
• The Aluminum was folded length-wise to make a strip 1 cm x 15 cm. The strip was coiled loosely to fit into a Copper Chloride solution in a beaker, making sure that the strip is entirely immersed.
• The beaker was heated gently on a hot pot for five minutes or until the blue colour in the solution had disappeared. It was heated gently for another 5 mins and was left to cool.
• Water was decanted in a waste beaker. Approximately 30mL of water was added to the reaction beaker and swirled to rinse the copper. Another decant was performed. The extra precaution was to be taken to avoid losing any copper while decanting.
• Tweezers were used to remove pieces of aluminum from the reaction beaker
• The mass of 1 piece of filter paper was recorded
• The filter paper was folded into a cone and placed in a funnel and was wet with water. Next, the copper and water was poured into the filer paper. The reaction beaker was rinsed with water to ensure all the copper had been transferred to the filter paper. Any visible pieces of aluminum were removed from the copper in the filter paper.
• The copper and filter paper was left to dry overnight
• The mass of the dry Copper and filter paper was recorded
• Hands were washed thoroughly after the experiment

Table 2: Quantitative (Grams)

 Analysis

• Calculate the theoretical yield of copper

M = MCu  + MCl  + MH20

= (63.55g) + 2 (35.45g) + 2 (18.02g)

= 170.41g

n = m/M

=2.00g/ 170.49g/mol

= 0.01173089331 mol

NCu= 0.01173089331 mol x 3 mol Cu    [therefore 3 mol CuCl2 . 2H20]

= 0.01173089331 mol

MCu= 63.55g/mol

MCu= 0.00173089331mol x 63.55g/mol

= 0.7454982699g

The theoretical yield of copper is 0.74g

• Identify the limiting reagent and the excess reagent in this reaction. What visible evidence is there to confirm your identification?

The limiting reagent was copper and the excess reagent was Aluminum.  This conclusion was confirmed when the Copper (11) Chloride Dihydrate, a blue solution, turned clear after it was heated proving it was limiting reagent. Aluminum was confirmed to be the excess reagent since it was unreactive, (after the Copper salt was formed) and was still present. Proving the Aluminum wasn’t completely consumed in the reaction.

• Determine the actual yield of copper

Mass of filter paper: 1.32g

Mass of Copper: 2.14g

2.14g – 1.315g

= 0.82g

The actual yield of Copper is 0.82g

•  Determine the percentage yield of copper in this experiment.

Percentage Yield Cu = (Actual yield / Theoretical yield) x 100%

= (0.82g/0.74g) x 100

= 110.81%

The percentage yield of Copper was 110.81%

• Suppose that the percentage yields was less than 100% suggest specific techniques or equipment that may account for a loss of product.

Specific techniques or equipment that may have accounted for a loss of products could have been the process of decanting, Copper could have been lost during that, and also during step 5, Copper may have been taken out while removing the Aluminum.

• Suppose that the percentage yield was greater than 100%. Suggest specific factors in the experiment that my account for this.   

There are various factors that may have accounted for this, one of which will be that not all the Aluminum was removed during step 5, another could be that the scale wasn’t zero properly when measuring the substances. Also, the presence of impurities in the Copper sample collected.

• What step did you take to ensure the reaction was complete

The step that was taken to ensure the reaction was completed was heating the beaker on the hot plate and stirring it until the blue Copper (11) dihydrate was clear.

• If you wanted to use aluminum as a limiting reagent, what changes in the procedure would be made? What visible evidence would u look for to ensure that the reaction had gone to completion

In order to make aluminum a limiting reagent, the amount of aluminum would have to be decreased and the amount of Copper (11) Chloride dihydrate would have to be increased. By doing this all of the Aluminum would be consumed in the reaction. Visible evidence would show that the reaction was complete and that there is no Aluminum left in the final product.

Conclusion

To conclude, the mass of the copper formed from the mass of Copper (11) Chloride dihydrate was 0.82g and the percentage yield was 110.81%