Q: Which of the following is the correct formula for the calculation of percent by mass of water in a hydrate?

$$\frac{\text{mass of water}}{\text{mass of hydrate}} \times 100\%$$

Question 1

Nickel(II) sulfate hexahydrate has the formula NiSO\_4·6H\_2O. How many moles of water are present in one mole of this compound?

Accepted Answer

$$6$$ moles$

Question 2

Calculate the mass of water in grams present in one mole of NiSO\_4·6H\_2O. (Molar mass of H\_2O = $$18.02\ \mathrm{g/mol})$$

Accepted Answer

$$108.12\ \mathrm{g}$$

Question 3

If you have $$2.100\ \mathrm{g} of $$NiSO\_4·6H\_2O, how many grams of water are present in this sample? (Molar mass of NiSO\_4·6H\_2O = $$262.85\ \mathrm{g/mol})$$

Accepted Answer

$$0.864\ \mathrm{g}$$

Question 4

What is the theoretical percent by mass of water in NiSO\_4·6H\_2O? (Molar mass of H\_2O = $$18.02\ \mathrm{g/mol}$$, molar mass of NiSO\_4·6H\_2O = $$262.85\ \mathrm{g/mol})$$

Accepted Answer

$$41.15\%$$

Question 5

A $$2.500\ \mathrm{g}$$ sample of NiSO\_4·6H\_2O is found to contain $$0.985\ \mathrm{g} of $$water. What is the experimental percent by mass of water in the sample?

Accepted Answer

$$39.4\%$$

Question 6

Calculate the percent error for the experimental percent of water found in the previous question, using the theoretical value $$41.15\%.$$

Accepted Answer

$$4.25\%$$

Question 7

Which of the following best describes a hydrate?

Accepted Answer

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

Question 8

If a student accidentally uses the molar mass of NiSO\_4 instead of NiSO\_4·6H\_2O when calculating percent water, what will be the effect on the calculated percent by mass of water?

Accepted Answer

The calculated percent by mass of water will be artificially low.

Question 9

A sample of NiSO\_4·6H\_2O is heated to remove all water. What is the mass of anhydrous NiSO\_4 left from a $$5.00\ \mathrm{g}$$ sample? (Molar mass of NiSO\_4 = $$154.76\ \mathrm{g/mol}$$, NiSO\_4·6H\_2O = $$262.85\ \mathrm{g/mol})$$

Accepted Answer

$$2.94\ \mathrm{g}$$

Question 10

Which of the following is the correct formula for the calculation of percent by mass of water in a hydrate?

Accepted Answer

$$\frac{	ext{mass of water}}{	ext{mass of hydrate}} 	imes 100\%$$

Question 11

A student determines the mass of water lost from a hydrate by heating. Which experimental error would cause the calculated percent water to be too low?

Accepted Answer

Not heating the sample long enough, so not all water is removed.

Question 12

If $$0.500\ \mathrm{mol} of $$NiSO\_4·6H\_2O is used, how many grams of water are present?

Accepted Answer

$$54.06\ \mathrm{g}$$

Question 13

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

Accepted Answer

Hydrates can affect the stability, solubility, and bioavailability of drugs.

Question 14

A $$10.0\ \mathrm{g}$$ sample of NiSO\_4·6H\_2O is heated and loses $$4.12\ \mathrm{g} of $$water. What is the percent by mass of water lost?

Accepted Answer

$$41.2\%$$

Question 15

Which of the following is NOT a correct step in determining the percent by mass of water in a hydrate experimentally?

Accepted Answer

Add water to the sample after heating.

Question 16

A hydrate sample is found to contain $$2.00\ \mathrm{g} of $$water and $$3.00\ \mathrm{g} of $$anhydrous salt. What is the percent by mass of water in the hydrate?

Accepted Answer

$$60.0\%$$

Question 17

Which of the following statements about the formula NiSO\_4·6H\_2O is correct?

Accepted Answer

There are six water molecules for every one formula unit of NiSO\_4.

Question 18

If a hydrate is exposed to air and absorbs water, what term best describes this process?

Accepted Answer

Deliquescence

Question 19

Which of the following is a common use of nickel(II) sulfate hexahydrate in industry?

Accepted Answer

Electroplating

Study Notes: Hydrates and Percent Composition – Nickel(II) Sulfate Hexahydrate

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