Rachel HandyMr. KnoxNovember 17, 2014SCH 3U

Percentage Yield Lab

Purpose: To determine the percentage yield in the isolation of pure copper, from iron and the aqueous solution of copper (ll) chloride.

Materials: 2 Beakers (250mL) Electronic balance, accurate to two decimal places Small beaker with distilled water 0.949g of rust-free, degreased steel wool 1mol/L of hydrochloric acid (HCl) Stirring rod Distilled water Hot plate 4.963g of copper (ll) chloride (CuCl2)

Procedure:1. Two clean, dry 250mL beakers were labelled with the initials of group member.2. 50mL of distilled water was added to beaker.3. Mass of steel wool was recorded.4. 4.963g of CuCl2 was added to water and was stirred until dissolved.5. Steel wool was added to CuCl2 solution in beaker. Stirring rod was used to ensure that reaction was complete.6. New solution was decanted into second 250mL beaker by pouring down glass stirring rod.7. Beaker was rinsed twice with distilled water and decanted again down glass stir rod into other beaker.8. 10mL of 1mol/L hydrochloric acid was added to beaker to further wash copper. The HCl was decanted and copper was washed again with distilled water. Final wash was done with distilled water to ensure that copper was clean.9. Beaker was left to dry out for two hours.10. Clean copper at bottom of beaker was placed on warm hot plate to dry out.11. Mass of beaker which contained dry copper was found.12. All equipment was cleaned and leftover substances were properly disposed of.

Observations: Quantitative ObservationsCopper (ll) chloride (CuCl2)Steel Wool (Fe)Beaker MassDried Copper and BeakerCopper Recovered

4.963g0.949g104.761g106.400g1.639g

Qualitative ObservationsBEFORE-CuCl2 Brown, powdery, dull-Fe Silver, shiny, rough-H2O Distilled water, clear, colourless, odourless DURING-CuCl2 (aq) mixed with iron creating a pale cobalt blue liquid, displacing the copper-The blue substance was warm in the beakerAFTER-After decanting, muddy brown solution is left-After heating, a light brown powdery mixture was left in beaker with green flakes from oxidation

Analysis: Fe(S) + CuCl2 (aq) FeCl2 (aq) + Cu (S)1.The theoretical yield of copper (Cu (S)) is...CuCl2 (aq)+Fe (S)FeCl2 (aq)+Cu (S)

Mass (m)

4.963g0.949g1.079838g

Molar Mass (M)

134.45g/mol55.85g/mol 63.55g/mol

Moles (n)

0.036913mol0.16991943mol0.16991943mol

Ratio

11

11

Therefore the theoretical yield of copper (Cu) is 1.079838g.2.The excess reactant is...CuCl2 (aq)Fe (S)

Mass (m)

4.963g0.949g

Molar Mass (M)

134.45g/mol55.85g/mol

Moles (n)

0.036913mol0.016992mol

Ratio

11

Working Line0.036913mol0.016992mol

Therefore iron (Fe (S)) is the excess reactant because it has a smaller 1 than copper (ll) chloride (CuCl2 (aq)). This means that iron will run out as a reactant before copper (ll) chloride.

3.The amount of copper actually recovered was...mbeaker= 104.761gmbeaker w/ Cu= 106.400gmCu= ?

mCu = mbeaker w/ Cu - mbeakermCu = 106.400g 104.761gmCu = 1.639g

Therefore the amount of copper actually recovered was 1.639g.

4.The percentage yield of copper was...

Therefore the percentage yield of copper was 151.8%.Discussion:Due to experimental error, the percentage yield of copper was not exactly 100%; it was calculated to be 151.8%. The most likely source of error that occurred in the lab was; that rather than having a mass of just copper, there was a solution of copper oxide making the mass of what was thought to be just copper much larger. Due to the inaccurate mass of copper measured, the percentage yield of copper was higher than 100%.In order to attain an improved percentage yield if the lab was to be completed again, the length of time that the copper was left out to dry would have been shortened to ensure that oxygen didnt interfere with the solution. Also, during the reaction, it would have been beneficial to let the iron absorb more into the solution than it had time for in the first lab. If these steps had been taken, a percentage yield closer to 100% may have been attained.Other metals that could have been used to perform a similar reaction to isolate copper would have been nickel, cadmium, aluminum, calcium, potassium etc... (everything that falls above copper on the Activity Series of Metals.)

Conclusion:The percentage yield of copper in the reaction between iron and the aqueous solution of copper (ll) chloride was 151.8%.