DATA AND OBSERVATIONS:
a) Mass of empty beaker and label:
b) Mass of weighing paper:
c) Mass of weighing paper and powdered iron:
d) Mass of beaker, label, and solid product:
110.765g
0.710g
2.255g
112.340g
Copper (II) sulfate pentahydrate - light blue, chunky, opaque, dull powder.
Copper (II) sulfate solution - blue transparent solution.
Iron powder - black opaque powder.
Copper produced - redish-black clumpy opaque powder.
CALCULATIONS:
1) Mass of powdered iron reacted:
2.255g
(mass of paper and iron)
- 0.710g
(mass paper)
= 1.545g
2) Moles of iron reacted:
1.545g Fe 1 mole Fe = 0.02766 moles Fe
55.85g Fe
3) Mass of copper produced:
112.340g
(mass of beaker, label, and copper)
- 110.765g
= 1.575g
(mass of beaker and label)
4) Moles of copper produced:
1.575g Cu 1 mole Cu = 0.02478 moles Cu
63.55g Cu
5) Ratio of iron-to-copper:
0.02766 moles Fe = 1.116
0.02478 moles Cu
6) Percent error for the molar ratio (accepted is 1.000:1):
(1.116 - 1.000) x 100 = 11.6 %
1.000
QUESTIONS:
1) Iron (II):
CuSO4 + Fe => FeSO4 + Cu
Iron (III):
CuSO4 + Fe => Fe2 (SO4 )3 + Cu
3CuSO4 + 2Fe => Fe2 (SO4 )3 + 3Cu
2) The reaction occurred with iron (II), CuSO4 + Fe => FeSO4 + Cu. The accepted
molar ratio for our experiment is 1 to 1, which is present in the balanced equation using
iron (II) but not present in the balanced equation using iron (III). The iron (III) equation
has an iron-to-copper molar ratio of 2 to 3.
3) We used the quantity of powdered iron instead of the quantity of copper (II) sulfate
because the copper (II) sulfate was ground into a rather chunky powder. Since the iron
was a very fine powder it was much easier to control the mass of our iron with much
more precision than it was to control the mass of the copper (II) sulfate. Also, since our
copper (II) sulfate was in excess in this experiment it makes more sense to do our
calculations using the iron and add a little extra copper (II) sulfate to insure that the iron
reacts completely.
4) Most likely the biggest assumption we made while performing this lab was the fact
that the copper that was left in the beaker was pure copper. Another large assumption that
was made was that enough copper (II) sulfate was used to completely react with the iron.
5) The mass of copper produced would seemingly be more if the sample of copper was
not fully dry before the final weighing. This was somewhat avoided by allowing the
washed sample of copper to sit overnight and dry before the final weighing the next day.
6) If the sample was not completely dry before weighing it would distort the ratio of ironto-copper in a way that would make it result in a negative error. This is because the
additional mass of the water would be converted to moles as though it had the same
density as copper, which it does not. This would result in a larger denominator, giving
you a negative error.
7) One of the biggest sources of error for this experiment is an incomplete washing. The
washing step was in the procedure to hopefully get rid of (or minimize) the amount of
iron (II) sulfate or unreacted iron left when the product was dry and ready for its final
weighing. Any foreign material still present in the beaker at the time of the final weighing
would distort the results. Another source of error could be not dissolving enough copper
(II) sulfate to insure that all of the iron completely reacted. This would result in rust the
next day, giving you a skewed final mass measurement.
8) As explained in the previous question, the purpose of washing the product was to
eliminate any traces of iron (II) sulfate, which would crystallize and throw off the final
mass measurement. The washing step was added to insure an accurate final mass
measurement after the copper product had had a chance to dry overnight. If the product
was not washed, this would result in an error because the mass of the iron (II) sulfate
would be measured as though it had the molar mass of copper, which is substantially
lighter than iron (II) sulfate.
9) 2.000g Cu 1 mole Cu = 0.03147 moles Cu
63.55 g Cu
6.791g Ag 1 mole Ag = 0.06296 moles Ag
107.87g Ag
Copper-to-silver ratio: 0.03147 moles Cu = 0.4998
0.06296 moles Ag
Copper (I) nitrate:
Cu + AgNO3 => Ag + CuNO3
Copper-to-silver ratio: 1 mole Cu = 1.000
1 mole Ag
Copper (II) nitrate:
Cu + AgNO3 => Ag + Cu(NO3 )2
Cu + 2AgNO3 => 2Ag + Cu(NO3 )2
Copper-to-silver ratio: 1 mole Cu = 0.500
2 moles Ag
The other product is copper (II) nitrate because the copper-to-silver ratio 0.4998 is
essentially 0.500, which is the molar ratio corresponding to the balanced chemical
equation for copper (II) nitrate.