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RESULT and CALCULATION
Part A : Pre- Reduction With Zinc
Measurements Notes
Describe the changes caused by the reaction instep 1,2 and 3
Solution turns to black
What is removed by the washing and decantationin step 5
Water,
What copper compound is present in step 6 Copper sulphate,
Reduction with zinc
Measurement Notes
Describe the change caused by the reaction Solution becomes
colourless
What is present in the solution Zinc Sulphate,
What gas is formed in this reaction Sulphate gas
Part B : Post Reduction With Zinc
Measurements Notes
What is removed by washing in step 3 Copper, Cu
Initial mass copper 0.5 g
Mass of copper + evaporating dish 8.87 g
Mass of evaporating dish 7.54 g
Mass of recovered copper 0.83 g
Initial mass of copper = 0.5 g
Mass of copper + evaporating dish = 7.54 g
Mass of evaporating dish = 8.87 g
Mass of copper = 1.33 g
Mass of recovered copper = 1.33 g 0.5 g
= 0.83 g
Theoretical yield =
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=
= 1.94 g of Cu
Percent yield, =
=
= 42.7
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DISCUSSION
In the fume hood, as prepared by lab technician, 0.5g of copper
wire is placed into 250ml
beaker. Then it is added with 5ml of concentrated to the beaker.
Copper nitrate was produced
from the reaction as shown in the equation below. Green copper
turn to blue solution because copper
will produce the solution blue in colour.
Cu(s) + 4 HNO3(aq) -----> Cu(NO3)2(aq) + 2 NO2(g) + 2
H2O(l)
The Pre-Reduction experiment then continued by adding 100ml of
distilled water into 250mlbeaker. 30ml of 3.0 M NaOH is added into
the solution. Next, the solution is heat and stirred bymagnetic
stirrer and was stopped when it reached its boiling point. Copper
hydroxide is producedfrom the reaction as shown in the equation
below.
(NO3)2(aq) + 2 NaOH(aq) -----> Cu(OH)2(s) + 2 NaNO3(aq)
The solution turns to black when it was heat and stirred using
magnetic stirrer. It is the left tobe cooled down. The solution
turns to black as it contains copper oxide. The reaction is known
as
dehydration where water is removed. The equation below shows
that copper oxide was obtained fromthe reaction of dehydration.
Cu(OH)2(s) -----> CuO(s) + H2O(g)
Next, the solution is added with 15ml 0f 6.0 M of into the
beaker by using pipette. Asshown by the equation below, copper
compound that present in the reaction is copper sulphate.
Bluesolution will produce black precipitate that mix with
water.
CuO(s) + H2SO4(aq) -----> CuSO4(aq) + H2O(l)
For the step of reduction of zinc, 2.0g of 30 mesh zinc metal
all in once into pre- reduction
beaker and stir until the supernatant liquid is colourless. The
black solution now turns blue solutionand finally turns into
colourless. This is due to the present of zinc sulphate as the
product of thereaction. The left residue is copper.
CuSO4(aq) + Zn(s) -----> ZnSO4(aq) + Cu(s)
The PostReduction experiment is started by weighing the
evaporating dish and records itsmass. From the reduction of zinc,
when the gas evolution has ceased, the solution is decant and
the
precipitate is transferred to the evaporating dish. The
precipitate copper is washed with about 5ml of
distilled water, allowed it to settle and decant the solution.
The washing step is repeated. Next, 5ml ofmethanol is used to wash
the precipitate, allow it to settle and decant the methanol.
Finally, theprecipitate is washed by 5ml of acetone, allowed it to
settle and decant the acetone solution. Theevaporating dish is
heated to let the precipitate to dry. The bottom of the evaporating
dish is wipedand recorded its mass.
To get mass of recovered copper, this equation below is
used:
Mass of recovered copper = mass of copperinitial mass of
copper
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Initial mass of copper = 0.5 g
Mass of copper + evaporating dish = 7.54 g
Mass of evaporating dish = 8.87 g
Mass of copper = 1.33 g
Mass of recovered copper = 1.33 g 0.5 g
= 0.83 g
Theoretical yield =
=
= 1.94 g of Cu
Percent yield, =
=
= 42.7
It is impossible to get 100% because during the experiment, many
errors have occur such as
incorrectly measured mass of copper, zero error and many more.
If this error could be overcome, the
percent yield might be near to 100%.
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QUESTIONS
1. Determine the percent yield of copperTheoretical yield =
=
= 1.94 g of Cu
Percent yield, =
=
= 42.7
2. Complete and balance the following chemical equationsCu(s) +
4 HNO3(aq) -----> Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O(l)
Cu(NO3)2(aq) + 2 NaOH(aq) -----> Cu(OH)2(s) + 2 NaNO3(aq)
Cu(OH)2(s) -----> CuO(s) + H2O(g)
CuO(s) + H2SO4(aq) -----> CuSO4(aq) + H2O(l)
CuSO4(aq) + Zn(s) -----> ZnSO4(aq) + Cu(s)
3. Determine the colour of your copper sampleGreen
4. If the percent yield of copper was greater than 100% what are
the two possible errors thathave been made?
The number can never be 1100% or even, so we may have
incorrectly measured the copper
beforehand (zero error) and some of the copper that we come out
with still bound to another
compound making it appear heavier.
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CONCLUSION
The experiment was successful. As the objective is to gain some
familiarity with basic
laboratory procedure, some chemistry of typical transition
element, and also the concept of percentage
yield. Some mistakes might occur, which is incorrect reading of
apparatus and others are stated in
discussion section. The percent yield was reasonable which is
42.7%. As the experiment was done,
familiarity with basic laboratory and the concept of percent
yield were explored.
REFERENCES
1. 2009, Chemistry, The Central Science, Pearson Educational
Malaysia2. 200, Focus Super Hot SPM Chemistry, Pelangi Malaysia3.
2000, General Chemistry with Quanlitative Analysis, Saunders
College
