One Day Later
11) Dry the beaker and weigh when cool and dry.
Results:
Observations Day 1:
The copper was initially a pink color. When dropped into the solution, it turned a grey colour, and a yellow fuzzy coating formed around the copper.
Observations Day 4:
The yellow coating formed around the copper had managed to grow, and, upon close inspection, were seen as crystals, and now had a sandy-like color. The crystals had completely engulfed the copper remaining, and when the copper coil remains were found after moving the crystals, the coil had decreased in size. Slivers of the copper coil could be seen in the mixture of crystals and copper, but could not be lifted out with the tweezers.
Observations Day 5:
The crystals had dried to form a crust at the bottom of the beaker.
Data Processing: Error Calculations:
Copper used=
Mass of copper before immersion
in solution – Mass of copper at the close
of the experiment=
0.44g – 0.12g= (0.01/0.44 + 0.01/0.12) × 100
0.32g = +10.6%
Mass of Silver (Actual Yield) =
Mass of beaker and silver – Mass of Beaker=
117.80g – 116.79g = (0.01/117.80 + 0.01/116.79) × 100
1.01g = +0.0171%
For the reaction
Cu (s) +2Ag+ (aq) Cu+2 (aq) + 2Ag (s)
0.32g Copper ÷ 63.55g mol-1
= 0.00504 moles (3sf)
For every mole of copper there is two moles of
silver
0.00504 moles copper × 2 = 0.0101 moles silver (3sf)
0.0101 moles silver × 107.87 g mol-1= 1.08g silver (3sf)
Therefore the theoretical yield of silver is 1.09g (3sf).
Percentage Yield=
(Actual Yield ÷ Theoretical Yield) × 100=
(1.01÷1.09) × 100=
93.0% (3sf)
Therefore the percentage yield is 93.0% (3sf).
Conclusion
The copper reacted with the silver nitrate to form copper nitrate and a coating on the outside of the copper. This formed a 93% percentage yield of silver.
Error analysis
The percentage yield is 93.0% - more silver crystals could have been formed.
The results could be due to: copper reacting with something other than silver, unreacted silver nitrate and systematic error.
Copper is near the bottom of the reactivity series, but could react with other items in its surroundings- like oxygen, or impurities in the silver nitrate. This can be dealt with by ensuring the copper is sanded perfectly before being placed inside the beaker, and ensuring the silver nitrate is purely silver nitrate- and water, if the silver nitrate is diluted.
Some of the silver nitrate will not have reacted with the copper- since there is more silver formed than copper nitrate, the silver nitrate was to excess. Therefore there must have been some of the unreacted silver nitrate left that was marked as having reacted with the copper. Also not all of the copper reacted, as flecks of copper were observed in the mixture while looking for some copper, and could not be removed. A more pragmatic way of ensuring all of the silver nitrate reacted is to add the silver nitrate 10mLs at a time and rubbing the silver crystals that form on the copper off every time and collect the crystals, until all of the copper reacted. Then record the amount of silver nitrate added to the copper.
There is also the possibility of systematic error, as the volume of silver nitrate was measured using the marks on the beaker. This could increase the uncertainty and thus increase the error percentage. This can be avoided by using a measuring cylinder to accurately measure the amount of substance being poured into the beaker.