Handout Investigation: How Much Water is in the Hydrate?

Name: Group #: Lab Date/Time:

Introduction: When chemical compounds incorporate water into their crystalline structure, they are called hydrates. Two salts were studied in the course of this investigation. First, a hydrate with a known molar ratio of water to salt was studied: copper sulfate pentahydrate, CuSO₄ •5H₂O. By heating the hydrate, the water was driven off. After dehydrating the sample, the molar ratio of water to copper sulfate was determined. Next, an unknown hydrate was studied. A procedure was developed to determine the molar ratio of water to salt for a provided unknown hydrate, (circle )MgSO₄•XH₂O /FeSO₄•XH₂O. The percent by mass of water in the sample and the empirical formula of the hydrate were determined.

Procedure: In this section, describe what your group did in both parts of the investigation in a paragraph format. Remember: **PAST TENSE!** (do not list/number procedures; use paragraphs).

-When recording mass all numbers should be recorded and never rounded.

-Include equipment, materials used, and concentration of any chemicals

-Explain the details about the procedure for the known hydrate (Part 1) and designing the procedure used for the unknown hydrate (Part 2). Be concise and descriptive.

-Describe any safety precautions taken within the procedure you followed.

-Describe any other procedures you also tried (if applicable).

-This section should be detailed enough that another group could duplicate your work, but do not include descriptions or analysis of the observed or calculated results so as to not overlap with the results and discussion sections.

Results:

For Part 1, copper sulfate pentahydrate was studied to confirm the validity of the technique. Upon heating the sample of the hydrate, the percent by mass of water in the hydrate was determined, as can be seen in Table 1

Write a descriptive title for this table.

Table 1:

If % of the mass of the hydrate is water, % of the initial mass is due to the copper sulfate.

For Table 2, the masses of hydrated salt and water were divided by their molecular weights to determine the moles of anhydrous salt and moles of water present. The ratio of moles of water to anhydrous salt gave a molar ratio used to propose an empirical formula for the hydrated salt.

Write a descriptive title for this table.

Table 2:

For Part 2, an unknown hydrate was analyzed. Table 3 shows the mass percent water of hydration for the salt.

Write a descriptive title for this table.

Table 3:

For Table 4 the masses of hydrated salt and water were divided by their molecular weights to determine the moles of anhydrous salt and moles of water present. The ratio of moles of water to anhydrous salt gave a molar ratio used to propose an empirical formula for the hydrated salt.

Write a descriptive title for this table.

Table 4:

The following sample calculation was used to determine the moles of water and anhydrous salt from the masses using the molecular weights. Data from Table was used.

Sample Calculation 4:

determined. When converted to a molar ratio, the results should be consistent with the true formula of CuSO₄ •5H₂O with a ratio of 5:1, water to anhydrous salt.

Briefly describe how your results compared to the 5:1ratio. State if your ratio was low or high, and explain why.

The same procedure was followed for the determination of % mass of hydration and empirical formula mole ratio for the unknown hydrate, (circle) MgSO₄•XH₂O /FeSO₄•XH₂O. The data in Tables 3, and 4 show the results of this analysis. It was determined that (circle) MgSO₄•XH₂O/FeSO₄•XH₂O has a %mass of hydration of ________, and an empirical formula of _______.

There are several possible sources of error and corrections that may have prevented each error. Fill in the table below, noting any experimental details or incongruences that may have led to errors in the results obtained. ("Human error" is not an acceptable response, be more specific.)

Error Possible Corrections

Conclusion:

Summarize the results obtained by this experiment:

The procedure developed during application of this experiment allowed/ did not allow for a successful analysis of hydrate samples for the following reasons:

Alternate methods or approaches:

Works Cited:

ACS Style. Use at least one reputable source other than your lab manual on the space provided below.

Bauer, R., Birk, J., Sawyer, D. Laboratory Inquiry in Chemistry, 3rd ed.; Brooks/Cole Cengage Learning: Belmont, 2009.