Experiment 3 Report Sheet Hydration of Epsom Salt Data Collection ✓ Solved

Collect data for the hydration of Epsom salt and address the following post-lab questions:

  1. How would your calculation of the average number of water molecules present in Epsom salt be affected if you heated your sample too strongly and too long and decomposition started to take place? (Too High, Too Low, Unchanged) Explain.

  2. How would the calculated number of water molecules present in Epsom salt be affected if the procedure was changed so the analysis was performed using 8.500g of hydrated salt instead of 1.500g? (Too High, Too Low, Unchanged) Explain.

  3. Calculate the mass percent of water contained in a sample of MgSO4.7H2O.

  4. A sample of raw mining ore contains a hydrated salt called copper sulfate pentahydrate, CuSO4.5H2O. If 10.000g of the ore loses 0.499g of water when heated strongly, what is the mass percentage of CuSO4.5H2O in the raw ore sample?

Paper For Above Instructions

The hydration of Epsom salt, known chemically as magnesium sulfate heptahydrate (MgSO4·7H2O), is a relevant experiment in chemistry that illustrates the principles of hydration and decomposition of hydrated salts. This experiment allows students to quantitatively analyze the composition of hydrated salts by studying the loss of water during heating and calculating the respective ratios of water molecules to the salt.

Impact of Overheating on Water Molecule Calculation

Heating a sample of Epsom salt too strongly and for too long may lead to the decomposition of the salt, which would affect the calculation of the average number of water molecules present in the compound. Specifically, if this decomposition occurs, it would result in a lower mass of the residue remaining, leading to a calculation of a lower number of moles of water lost. Therefore, the correct conclusion regarding the average would be that it is “Too Low,” due to the loss of both water and possibly some salt upon excessive heating.

Impact of Mass Variation on Water Molecule Calculation

If the mass of hydrated salt used for analysis was increased from 1.500g to 8.500g, the calculated number of water molecules would likely be “Unchanged.” The mole ratio is independent of the mass of the sample itself, as the dehydration process should theoretically yield the same proportions of water to salt. However, practical laboratory conditions, such as the effective heating and measurement accuracy, may vary with larger samples. Still, under ideal circumstances, the inherent ratio of moles should remain constant.

Calculation of Mass Percent of Water in MgSO4·7H2O

To calculate the mass percent of water in Epsom salt, we first need to determine the molar mass of MgSO4·7H2O. The molar mass is calculated as follows:

  • Magnesium (Mg): 24.31 g/mol

  • Sulfur (S): 32.07 g/mol

  • Oxygen (O): 16.00 g/mol (for 4 O in sulfate)

  • Water (H2O): 18.02 g/mol (for 7 water molecules)

The total molar mass of MgSO4·7H2O is:

24.31 + 32.07 + (4 × 16.00) + (7 × 18.02) = 246.47 g/mol

The mass of the water component is:

7 × 18.02 = 126.14 g

The mass percent of water is then calculated as follows:

(mass of water / total mass of hydrated salt) × 100 = (126.14 / 246.47) × 100 ≈ 51.19%

Mass Percentage of CuSO4·5H2O in Raw Ore Sample

In the case of copper sulfate pentahydrate (CuSO4·5H2O), similar calculations are necessary. The molar mass of CuSO4·5H2O is:

  • Copper (Cu): 63.55 g/mol

  • Sulfur (S): 32.07 g/mol

  • Oxygen (O): 16.00 g/mol (for 4 O in sulfate)

  • Water (H2O): 18.02 g/mol (for 5 water molecules)

The total molar mass of CuSO4·5H2O is:

63.55 + 32.07 + (4 × 16.00) + (5 × 18.02) = 249.69 g/mol

Next, we calculate the mass of water lost:

0.499g of water lost corresponds to the weight of CuSO4·5H2O present. To find the total mass of CuSO4·5H2O in the ore sample, we can use the following proportion:

Let x be the mass of CuSO4·5H2O. The equation is:

0.499g / x = mass percent / 100

Rearranging gives:

x = 0.499g / (mass percent / 100)

Thus, the mass percentage of CuSO4·5H2O in the raw ore sample can be correlated to the total mass:

(10.000g - 0.499g) / 10.000g × 100 = (9.501g / 10.000g) × 100 = 94.99%.

Conclusion

The experiment of determining the hydration of Epsom salt and copper sulfate pentahydrate provides valuable insights into the composition of hydrated salts and the significant effects that heating can have on their chemical integrity. Understanding these principles is essential in various fields, including chemistry, environmental science, and material science.

References

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