Composition of a Copper Sulfate Hydrate Lab

Before heating:

During heating:

After heating:

Above are the photos of the hydrate before, during, and after heating the evaporating dish on the hot plate. Below I have included some calculations to find the empirical formula of the compound.

1) Calculate the mass of the hydrate used.

45.83g - 45.06g = 0.77g

2) Calculate the mass of the water lost.

45.83g - 45.58g = 0.25g

3) Calculate the percentage of water in the hydrate.

0.25g/0.77g = 32.5%

4) The accepted value for the percentage of water in this hydrate is 36.0%. Find your percent error and provide a possible explanation for your error.

percent error = [(experimental value - accepted value)/accepted value] x 100

= [(0.325 - 0.360)/0.360] x 100

= -9.27%

= 9.27%

There are various possible reasons for our error. For example, the scale fluctuated every time we checked the mass of the evaporating dish. Therefore, our calculations for the values of the substance could be inaccurate. Also, we may have lost a few grams of the hydrate when stirring the solid in the dish. I tried to break the larger crystals down so that more of the hydrate would be exposed to the heat. However, if I recall correctly, a piece of a hydrate crystal flew out of the evaporating disk.

5) Find the exact formula of the hydrate from your experimental data.

(a) Moles of water evaporated: 0.014 mol H20

(b) Moles of CuSO4 (anhydrate) that remain in evaporating dish: 0.0033 mol CuSO4

(c) Find the ratio of moles of CuSO4 to moles of H2O.

     1 CuSO4 : 4.24 H2O

(d) What is the empirical formula of the hydrate: 1 CuSO4 * 4 H2O

Our percent of error was 9.27%, which is not a huge one, but the formula above may be incorrect. For the percent of water in the hydrate to be closer to the accepted value of 36%, more water would have to be lost. We did not let the water evaporate from the hydrate enough. If more water had evaporated, the moles of water would increase. Subsequently, the ratio of moles of water to moles of copper sulfate hydrate would be greater than 4.24:1. Thus, if the coefficient 4 for H2O in the empirical formula is incorrect, I would predict the actual value to be slightly greater.

At the end of the lab, we added water to the hydrate, and found that it reverts to look like the original: