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In order to find the theoretical yield of Cu, the first step is to know the theoretical yield of CuCl2 (which is 2.00 grams) and then subtract the yield of Cl2 to end up only with Cu’s theoretical yield.
The theoretical yield’s formula is number of moles ; which is in short ()
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The theoretical yield of CuCl2 is
mol
mol
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The theoretical yield of Cu is
g
g
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The actual yield is found when the experiment is actually conducted, and it’s by weighing the amount of copper, after separating it from the aluminum in the solution. Afterwards, the actual yield is divided by the theoretical, and multiplied by 100, to find out the ‘percentage yield’.
Hypothesis
The assumed mass of copper is grams (theoretical yield), hence anything other than this explains that an error occurred during the experiment. If the actual mass of copper is within the range of grams, then the percentage yield is as close to 100% as possible and that the level of experimental errors is acceptable.
Variables
When the above equation is explained, it shows very clearly the dependent and independent variables. Here is the same equation rewritten, and logically explained.
3CuCl2. H2O + 2Al 2AlCl3 + 3Cu
Copper chloride in water + aluminum (yields when heat and agitating added) aluminum chloride + copper
Here it’s made very clear that the controls are: heat (temperature) and agitating (stirring and may include the other apparatus); the independent variable is aluminum (which excess and can’t be effected) and the reason it’s added in the solution is to take away the chlorine, but copper’s purity is affected if too much aluminum is added to the solution, so it’s simply a dependent variable.
Materials
The materials that are needed to conduct this experiment are:
- Goggles and lab coat
- Aluminum foil (8cm x 2cm)
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2.00 grams of copper chloride (CuCl2)
- Hot plate
- Forceps
- Distilled water (50 ml)
- Two 150 ml glass beakers
- 50 ml graduated cylinder
- Watch glass
- Stirring rod
- Tea spoon
- Grams measuring scale (balance) that shows up to two decimal places.
Method
The procedure for conducting the experiment:
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Pour 50ml of distilled water in the glass beaker using the graduated cylinder, then measure 2.00 grams of copper chloride (CuCl2), and dissolve it in the water.
- Fold an aluminum foil into a strip (8cm x 2cm). Coil the strip loosely to fit into the copper chloride solution in the beaker (strip is entirely immersed).
- Mix the solution using the stirring rod for around five minutes, and notice that the bright blue color of the copper changes to gray, and that’s a sign that the copper in the solution is being used.
- Gently heat the beaker to drive of the water.
- When all the water in the beaker vaporizes, transfer the dry copper (solid) to a watch glass using a tea spoon. Make sure the watch glass is on the balance and ‘zero the balance’, then determine the mass of copper.
Results
Some qualitative and quantitative observation on the experiment:
- The color of the solution changes from a bright blue color to a dark gray, and that’s when all the available copper been used (react with aluminum), and there is no left over copper, therefore there is no blue color in the solution anymore; which is the sign that the reaction went in completion.
- The smell release of the solution.
- Some bubbling sounds from the solution (a sign for a reaction).
- The solution in the beaker releases heat (energy release is a sign that a new product is formed). An exothermic reaction.
- When the water in the solution boils, the only substance remains in the beaker is copper (dark red solid copper)
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The actual yield of copper that is found in the experiment (the mass of copper) is grams; and this is way more than what’s expected, the theoretical yield is only grams. So, that shows that the percentage yield is divided by then multiplied by 100:
The result is much more than 100%, and this explains that errors took place during the experiment.
Discussion
The possible errors that may occur during the experiment, and were the reason why the percentage yield is very high, include the effect of water on the mass of copper; when the copper is separated from the solution, it may wasn’t absolutely dry and that what caused the copper to be heavier, which is in order what makes the percentage yield too high. Tiny particles of copper chloride were stuck in the tea spoon when transferring 2.00 g of copper chloride into the distilled water; it’s the same spoon that is used to transfer the wet solid copper after vaporization from the beaker to the glass watch.
Conclusion
All the results that are gathered shows that the exothermic reaction that based on evidences of color change, bubbling and temperature change went to a completion. However, the conducted experiment includes some kind of errors which leaded to a high percentage yield and an inaccuracy. Some suggestions might apply that help improving the experiment and ending with a more accurate percentage yield, such as:
- Using thin papers in separating the copper from the solution instead of boiling, because it makes sure that the copper is dry.
- Making sure not to use the same material (apparatus) twice, to avoid errors (e.g. stuck particles on the glass watch could give a heavier mass for copper).
Bibliography
- Abu-Dhabi Gas Industries Ltd. (GASCO), Shift Controller, Bu-Hasa Plant Division
Tel: 02-6035-455
Mobile: +971-50-8188-933
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Lesson Plans Page, 2010, [online], Available: [Accessed in 7 December 2010]
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, 2010, [online], Available: [Accessed in 11 December 2010]
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Stoichiometry of Aluminum and Copper (II) Chloride, [online], Available: [Accessed in 11 December 2010]
