Q: A student determines the mass of water lost from a hydrate and the mass of the anhydrous compound. Which formula should be used to calculate the number of moles of water lost?

$$\text{moles of water} = \dfrac{\text{mass of water}}{\text{molar mass of water}}$$

Q: If the molar mass of $$\mathrm{$$CuSO_4$$} is$$ $$159.6\ \mathrm{g/mol}$$ and the molar mass of $$\mathrm{H_2O} is$$ $$18.0\ \mathrm{g/mol}$$, what is the formula for calculating the number of moles of $$\mathrm{$$CuSO_4$$} in a $$sample?

$$\text{moles of $$CuSO_4$$} = \dfrac{\text{mass of $$CuSO_4$$}}{159.6}$$

Question 1

Which of the following best describes a hydrate?

Accepted Answer

A compound that contains a fixed number of water molecules chemically combined with the metal ion.

Question 2

What is the main difference between an anhydrous and a hydrated compound?

Accepted Answer

Anhydrous compounds have had their water of hydration removed, while hydrated compounds contain a fixed number of water molecules chemically combined.

Question 3

A student heats a sample of $$\mathrm{$$CuSO_4$$\cdot 5H_2O}$$ and observes a color change from blue to white. What does this indicate?

Accepted Answer

The water of hydration has been removed, converting the hydrate to its anhydrous form.

Question 4

Which of the following compounds is deliquescent?

Accepted Answer

Sodium hydroxide ($$\mathrm{NaOH})$$

Question 5

A desiccant is used in a laboratory desiccator. Which property makes it suitable for this purpose?

Accepted Answer

It is hygroscopic and absorbs moisture from the environment.

Question 6

If a student starts with 0.1000 g of $$\mathrm{$$CuSO_4$$\cdot 5H_2O}$$ and after heating, the mass of the anhydrous $$\mathrm{$$CuSO_4$$} is 0.0640 g$$, what is the mass of water lost?

Accepted Answer

$$0.0360\ \mathrm{g}$$

Question 7

Given the following data: mass of hydrate = $$0.1200\ \mathrm{g}$$, mass of anhydrous compound after heating = $$0.0800\ \mathrm{g}$$, calculate the mass of water lost.

Accepted Answer

$$0.0400\ \mathrm{g}$$

Question 8

A student determines the mass of water lost from a hydrate and the mass of the anhydrous compound. Which formula should be used to calculate the number of moles of water lost?

Accepted Answer

$$	ext{moles of water} = \dfrac{	ext{mass of water}}{	ext{molar mass of water}}$$

Question 9

If the molar mass of $$\mathrm{$$CuSO_4$$} is$$ $$159.6\ \mathrm{g/mol}$$ and the molar mass of $$\mathrm{H_2O} is$$ $$18.0\ \mathrm{g/mol}$$, what is the formula for calculating the number of moles of $$\mathrm{$$CuSO_4$$} in a $$sample?

Accepted Answer

$$	ext{moles of $$CuSO_4$$} = \dfrac{	ext{mass of $$CuSO_4$$}}{159.6}$$

Question 10

A student finds that the ratio of moles of water to moles of anhydrous $$\mathrm{$$CuSO_4$$} is 5$$:1. What is the correct formula for the hydrate?

Accepted Answer

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

Question 11

Which of the following statements about hygroscopic substances is correct?

Accepted Answer

Hygroscopic substances absorb water from the atmosphere, but not all are hydrates.

Question 12

A student is given an unknown hydrate and determines the following: mass of hydrate = $$0.1500\ \mathrm{g}$$, mass of anhydrous compound = $$0.1000\ \mathrm{g}. If $$the anhydrous compound is $$\mathrm{$$MgSO_4$$}$$ ($$120.4\ \mathrm{g/mol}$$), calculate the number of moles of $$\mathrm{$$MgSO_4$$}$$ present.

Accepted Answer

$$0.00083\ \mathrm{mol}$$

Question 13

In the experiment, why is it important to heat the micro-crucible containing the anhydrous compound multiple times until a constant mass is achieved?

Accepted Answer

To ensure all water of hydration has been removed from the compound.

Question 14

A student calculates the moles of water and moles of anhydrous compound in a hydrate. Which formula should be used to determine the empirical formula of the hydrate?

Accepted Answer

$$	ext{Empirical formula} = 	ext{Anhydrous compound}\cdot n	ext{H}_2	ext{O}$$, where $$n = \dfrac{	ext{moles of water}}{	ext{moles of anhydrous compound}}$$

Question 15

Which of the following is NOT a correct example of a hydrated salt?

Accepted Answer

$$\mathrm{NaCl\cdot 3H_2O}$$

Question 16

A student is given $$0.2000\ \mathrm{g} of$$ $$\mathrm{$$ZnSO_4$$\cdot zH_2O}$$ and after heating, the mass of anhydrous $$\mathrm{$$ZnSO_4$$} is$$ $$0.1400\ \mathrm{g}. If $$the molar mass of $$\mathrm{$$ZnSO_4$$} is$$ $$161.5\ \mathrm{g/mol}$$ and $$\mathrm{H_2O} is$$ $$18.0\ \mathrm{g/mol}$$, what is the value of $$z in $$the hydrate formula?

Accepted Answer

$$z = 7$$

Question 17

Which of the following statements about deliquescence is correct?

Accepted Answer

Deliquescent substances absorb enough water to dissolve themselves in the absorbed water.

Question 18

In a real-world scenario, why are desiccant packets placed in pill bottles?

Accepted Answer

To prevent pills from absorbing moisture and degrading.

Question 19

A student is given $$0.1800\ \mathrm{g} of$$ $$\mathrm{$$CaSO_4$$\cdot xH_2O}$$ and after heating, the mass of anhydrous $$\mathrm{$$CaSO_4$$} is$$ $$0.1500\ \mathrm{g}. If $$the molar mass of $$\mathrm{$$CaSO_4$$} is$$ $$136.1\ \mathrm{g/mol}$$ and $$\mathrm{H_2O} is$$ $$18.0\ \mathrm{g/mol}$$, what is the value of $$x in $$the hydrate formula?

Accepted Answer

$$x = 2$$

Hydrates: Properties, Analysis, and Laboratory Determination

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