Lab report #3 - professor: Holland Lab TA: Trammel PDF

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professor: Holland
Lab TA: Trammel...

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Taylor Herrera Lab partner: Amanda Oldham

2/13/17

Chem 200, Experiment #3 Limiting Reagent of Solutions Procedure See the pre-lab report for an outline of the general procedure. No changes to the procedure were made during the experiment. Experimental Data Part A Weight of a watch glass Weight of watch glass + filter paper Weight of watch glass + filter paper right after filter paper dried Weight of watch glass + filter paper after another 10 minutes on the water bath Weight of watch glass + filter paper after another 5 minutes on the water bath Calculated Data Part A moles of CaCl2 Moles of Na2CO3 Number of moles of CaCO3 expected Limiting agent Mass of CaCO3 Actual yield Theoretical yield Percent yield

20 mL of 0.5 M CaCl2 51.536g 52.404g

25 mL of 0.5 M CaCl2 19.133g 19.988g

54.125g

20.630g

53.963g

20.599g

53.850g

20.588g

20 mL of 0.5 M CaCl2 0.01mol 0.015mol 0.01mol

25 mL of 0.5 M CaCl2 0.0125mol 0.0075mol 0.0075mol

Na2CO3 1.446g 1.64 1.0 164%

CaCl2 0.6g 0.6265 0.75065 83.46%

Part B Balanced equation of the reaction of Copper sulfate with sodium hydroxide: 2NaOH (aq) + CuSO4 (aq)  Na2SO4 (aq) + Cu(OH)2 (s) Ratio of CuSO4:NaOH

Observations

4

Drops of 0.1M sodium hydroxide, NaOH 20

1:5

2

8

16

1:2

3

12

12

1:1

4

16

8

2:1

5

20

4

5:1

Dark blue on top, light blue chunks floating on bottom (1/2 precipitate) Dark blue color in the middle (1/3 precipitate) Dark blue towards top, light blue on bottom (1/4 precipitate) Light blue/chunky on bottom (1/3 precipitate) Has the most liquid – light blue chunks floating on bottom/middle (1/2 precipitate)

Test tube #

Drops of 0.1 M copper sulfate, CuSO4

1

Discussion questions: 1. I thought our data was very precise because of numbers were all very close in range, but the accuracy was not as accurate because our calculated numbers were not as close as they could have been to the actual amounts. A systematic error could be when we were adding 20mL and 25mL of 0.5 M CaCl2, the amounts were not perfectly at the 20 or 25 mL mark. Also the filter paper may not have been completely dry when we first took it off the wash bath. A random error could be the balance not giving us the exact mass of a substance (it may have been off by 0.01 or so). 2. The pattern I noticed was that the tubes with the most precipitate had the smallest ratio. Tubes 1 and 5 had the most precipitate and their ratios were 1:5 and 5:1

3. The mass of CaCO3 expected from our calculations of the 20 mL solution was 1.000869g and the mass expected from our calculations of the 25mL solution was 0.75065175. The actual amount obtained though was 1.446g for the 20 mL and 0.6 for the 25mL. For the 20mL, our calculated amount was less than the actual amount and for the 25mL solution, our calculated amount was more than the actual amount 4. If you touched the filter paper with wet fingers right before weighing, the mass would be thrown off because the filter paper would appear to weigh more than it actually does. That would then throw off the calculation for the solids mass because you would be using inaccurate numbers since when the paper dries after you touch it, it will weigh less. 5. If some of the solid is not washed out of the beaker, the mass of solid collected will be lower than what it is supposed to be, therefore the mass percentage for the limiting reactant will also be lower than expected....