The texture after the heating appeared to look like ash, suggesting that it was dryer.
Questions:
- Calculate the mass of water in the hydrate.
Total mass of water: Weight before heating – Weight after heating #4
48.72 ± 0.02 – 47.75 ± 0.02 = 0.97g
Uncertainty of mass of water in hydrated salt:
0.02 + 0.02 = 0.04
Total mass of water = 0.97 ± 0.04
- Compare the number of the anhydrous compound to the number of moles of water in the hydrate and use the ratio of these values to predict a formula of the hydrated compound.
Mass of anhydrous compound:
2.98 ± 0.04 - 0.92 ± 0.04 = 2.06 ± 0.08
Moles of anhydrous compound:
n = m/M
n = 2.06/ (63.55 + 32.07 + 16.00 + 16.00 + 16.00 + 16.00)
n = 0.0129
n ≈ 0.013
Moles of water in hydrated compound:
n = m/M
n = 0.92/ (1.008 + 1.008 + 16.00)
n = 0.051
Ratio of Moles of anhydrous compound to Moles of water in hydrated compound
0.013 : 0.051
Divide by the smaller ratio
0.013/ 0.013 = 1
0.051 / 0.013 = 3.9 ≈ 4
Whole number Ratio of Moles of anhydrous compound to Moles of water in hydrated compound:
1 : 4
Predicted formula for anhydrous compound:
CuSO4 .4H2O
Uncertainty for Moles of anhydrous compound:
(0.08/ 2.06) x 100 = 3.88%
(3.88/ 100) x 0.013 = 0.0005
Moles of hydrated compound
0.0130 ± 0.0005
Uncertainty for Moles of water in hydrated compound:
(0.04/ 0.92) x 100 = 4.35%
(4.35/ 100) x 0.051 = 0.002
Moles of water in hydrated compound
0.051 ± 0.002
- Determine the percentage of water in the hydrated crystals
Percentage of water in hydrated crystals
(0.97 / 2.98) x 100 = 32.55%
Uncertainty of Percentage of water in hydrated salt:
(0.04/0.97) x 100 = 4.12%
(0.04/2.98) x 100 = 1.34%
4.12 + 1.34 = 5.46%
(5.46/ 100) x 32.55 = 1.78 ≈ 2
Percentage of water in hydrated salt:
33± 2%
- Calculate the percentage of water obtained from the formula. What is the error?
Formula: CuSO4 .5H2O
Ratio – 1:5
Percentage of water:
1 + 5 = 6
(5/ 6) x 100 = 83.33%
Error:
83.33% – 32.55 ± 2% = 50.78 ± 2%
- What is the percentage error?
Percentage error:
[(Experimental value – Theoretical value)/ Theoretical value] x 100%
[(32.55 – 83.33)/ 83.33] x 100%
= [(-50.78)/ 83.33] x 100%
= -60.94%
= 60.94%
Uncertainty in Percentage error:
(2/ 32.55) x 100 = 6.14%
(6.14/ 100) x 60.94 = 3.74
Percentage error:
60.94 ± 3.74%
Data Presentation and Processing:
Table 2: Table of Calculated Data
Conclusion:
The value that has been worked out is close to the theoretical value, however, the theoretical value is not within the uncertainty of the value that has been calculated. Therefore, there is a major error within this experiment. This could be caused by the lack of time to finish the experiment, ending up with not enough time to finish heating the compound. The fourth heating was a lot shorter than what it was meant to be (10 minutes), and so not all the water has been vapoured out of the compound, causing major uncertainties within the values recorded.
Evaluation: