Question 1

A student heated a hydrate sample in a crucible. The mass of the empty crucible was $$17.95\ \mathrm{g}$$, the mass of crucible and hydrate was $$27.16\ \mathrm{g}$$, and the mass of crucible and anhydrous salt after heating was $$26.07\ \mathrm{g}. $$What is the mass of water lost during heating?

Accepted Answer

$$1.89\ \mathrm{g}$$

Question 2

Given the following data: mass of crucible and hydrate $$= 27.16\ \mathrm{g}$$, mass of empty crucible $$= 17.95\ \mathrm{g}$$, and mass of crucible and anhydrous salt $$= 26.07\ \mathrm{g}. $$What is the mass of the hydrate sample used?

Accepted Answer

$$9.21\ \mathrm{g}$$

Question 3

If the mass of anhydrous salt is $$8.32\ \mathrm{g}$$ and the mass of water lost is $$1.89\ \mathrm{g}$$, what is the percent by mass of water in the hydrate?

Accepted Answer

$$22.7\%$$

Question 4

A hydrate sample loses $$1.89\ \mathrm{g} of $$water upon heating. If the molar mass of water is $$18.02\ \mathrm{g/mol}$$, how many moles of water were lost?

Accepted Answer

$$0.105\ \mathrm{mol}$$

Question 5

If the mass of anhydrous salt is $$8.32\ \mathrm{g}$$ and the salt is assumed to be $$\mathrm{$$CuSO_4$$} ($$molar mass $$159.61\ \mathrm{g/mol}$$), how many moles of anhydrous salt are present?

Accepted Answer

$$0.0521\ \mathrm{mol}$$

Question 6

Using your answers from previous questions, what is the experimental value of $$x in$$ $$\mathrm{$$CuSO_4$$} \cdot x\mathrm{H_2O}$$ for this hydrate sample?

Accepted Answer

$$5$$

Question 7

A student did not heat the hydrate sample long enough, leaving some water in the sample. How would this affect the calculated percent by mass of water in the hydrate?

Accepted Answer

The percent by mass of water would be too low.

Question 8

Which of the following best describes a hydrate?

Accepted Answer

A compound that contains water molecules chemically bonded within its crystal structure.

Question 9

Why is it important to allow the crucible to cool before weighing after heating a hydrate?

Accepted Answer

Because a hot crucible can give a falsely high mass reading due to convection currents.

Question 10

A student finds the mass of water lost to be $$1.89\ \mathrm{g}$$ and the mass of anhydrous salt to be $$8.32\ \mathrm{g}. If $$the molar mass of the anhydrous salt is $$159.61\ \mathrm{g/mol}$$ and the molar mass of water is $$18.02\ \mathrm{g/mol}$$, what is the empirical formula of the hydrate?

Accepted Answer

$$\mathrm{$$CuSO_4$$} \cdot 5\mathrm{H_2O}$$

Question 11

If a hydrate is overheated and some of the anhydrous salt decomposes, how will this affect the calculated value of $$x in$$ $$\mathrm{$$CuSO_4$$} \cdot x\mathrm{H_2O}$$?

Accepted Answer

The calculated value of $$x$$ will be too low.

Question 12

A hydrate sample is found to contain $$22.7\%$$ water by mass. If the molar mass of the anhydrous salt is $$159.61\ \mathrm{g/mol}$$ and the molar mass of water is $$18.02\ \mathrm{g/mol}$$, what is the theoretical value of $$x in$$ $$\mathrm{$$CuSO_4$$} \cdot x\mathrm{H_2O}$$?

Accepted Answer

$$5$$

Question 13

Which of the following is a correct step in determining the formula of a hydrate from experimental data?

Accepted Answer

Convert the mass of water lost and the mass of anhydrous salt to moles, then find the simplest whole number ratio.

Question 14

A hydrate is heated and the mass of the sample decreases. What does this indicate about the composition of the hydrate?

Accepted Answer

Water is being driven off from the hydrate.

Question 15

If a student accidentally spills some of the hydrate sample after weighing but before heating, how will this affect the calculated percent by mass of water?

Accepted Answer

The percent by mass of water will be too low.

Question 16

Which of the following best explains why hydrates are important in pharmaceutical storage?

Accepted Answer

Hydrates can affect the stability and shelf life of pharmaceutical compounds.

Hydrate Analysis: Determining Water Content in a Hydrated Salt

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