Q: What is the correct formula to calculate molar mass?

$$\text{Molar Mass} = \dfrac{\text{grams}}{\text{mole}}$$

Q: Calculate the molar mass of $$\mathrm{C_4H_7N_2O_2}$$ using the following atomic masses: C = 12.01 g/mol, H = 1.008 g/mol, N = 14.01 g/mol, O = 16.00 g/mol.

$$4 \times 12.01 + 7 \times 1.008 + 2 \times 14.01 + 2 \times 16.00 = 113.10\ \mathrm{g/mol}$$

Q: Given the atomic masses: N = 14.01 g/mol, H = 1.008 g/mol, S = 32.07 g/mol, O = 16.00 g/mol, calculate the molar mass of $$(NH_4$)_2SO_4.$$

$$2 \times 14.01 + 8 \times 1.008 + 1 \times 32.07 + 4 \times 16.00 = 132.14\ \mathrm{g/mol}$$

Q: A sample contains 3.00 moles of $$NiCl_2$$ \cdot 6H_2O$$. What is the total mass of the sample if the molar mass is 237.69$$\ \mathrm{g/mol}$$?

$$3.00 \times 237.69 = 713.07\ \mathrm{g}$$

Q: A student is asked to find the molar mass of $$C_2H_6O. $$Which of the following is the correct calculation?

$$2 \times 12.01 + 6 \times 1.008 + 1 \times 16.00 = 46.068\ \mathrm{g/mol}$$

Question 1

Which of the following best describes molar mass?

Accepted Answer

The mass of one mole of a substance, expressed in $$\mathrm{g/mol}.$$

Question 2

What is the correct formula to calculate molar mass?

Accepted Answer

$$	ext{Molar Mass} = \dfrac{	ext{grams}}{	ext{mole}}$$

Question 3

Calculate the molar mass of $$\mathrm{C_4H_7N_2O_2}$$ using the following atomic masses: C = 12.01 g/mol, H = 1.008 g/mol, N = 14.01 g/mol, O = 16.00 g/mol.

Accepted Answer

$$4 	imes 12.01 + 7 	imes 1.008 + 2 	imes 14.01 + 2 	imes 16.00 = 113.10\ \mathrm{g/mol}$$

Question 4

A compound contains 2 nitrogen atoms, 8 hydrogen atoms, 1 sulfur atom, and 4 oxygen atoms. What is its chemical formula?

Accepted Answer

$$(NH_4$)_2SO_4$$

Question 5

Given the atomic masses: N = 14.01 g/mol, H = 1.008 g/mol, S = 32.07 g/mol, O = 16.00 g/mol, calculate the molar mass of $$(NH_4$)_2SO_4.$$

Accepted Answer

$$2 	imes 14.01 + 8 	imes 1.008 + 1 	imes 32.07 + 4 	imes 16.00 = 132.14\ \mathrm{g/mol}$$

Question 6

Which step is necessary when calculating the molar mass of a compound with parentheses in its formula, such as $$(NH_4$)_2SO_4$$?

Accepted Answer

Distribute the subscript outside the parentheses to each element inside.

Question 7

Nickel(II) chloride hexahydrate has the formula $$\mathrm{$$NiCl_2$$ \cdot 6H_2O}. $$What is the correct way to calculate its molar mass?

Accepted Answer

Add the molar masses of Ni, 2 Cl, and 6 H$$_2O $$molecules.

Question 8

If you have 0.05567 mol of diazepam and its mass is 15.86 g, what is its molar mass?

Accepted Answer

$$\dfrac{15.86\ \mathrm{g}}{0.05567\ \mathrm{mol}} = 285.1\ \mathrm{g/mol}$$

Question 9

Which of the following is NOT a correct SI unit for molar mass?

Accepted Answer

$$\mathrm{g}$$

Question 10

A student calculates the molar mass of $$\mathrm{H_2SO_4} as$$ $$2 	imes 1.008 + 32.07 + 4 	imes 16.00. $$What is the result?

Accepted Answer

$$98.086\ \mathrm{g/mol}$$

Question 11

Which of the following compounds contains the greatest number of oxygen atoms per formula unit?

Accepted Answer

$$H_2SO_4$$

Question 12

A sample contains 3.00 moles of $$NiCl_2$$ \cdot 6H_2O$$. What is the total mass of the sample if the molar mass is 237.69$$\ \mathrm{g/mol}$$?

Accepted Answer

$$3.00 	imes 237.69 = 713.07\ \mathrm{g}$$

Question 13

Which step is performed first when calculating the molar mass of a compound?

Accepted Answer

Count the number of each element in the formula.

Question 14

A student is asked to find the molar mass of $$C_2H_6O. $$Which of the following is the correct calculation?

Accepted Answer

$$2 	imes 12.01 + 6 	imes 1.008 + 1 	imes 16.00 = 46.068\ \mathrm{g/mol}$$

Question 15

Why is it important to use the correct atomic masses from the periodic table when calculating molar mass?

Accepted Answer

Because atomic masses are unique to each element and affect the total molar mass.

Question 16

Which of the following is a correct real-world application of molar mass?

Accepted Answer

Determining the dosage of a medication based on its molar mass.

Question 17

A chemist needs 50.0 g of $$C_4H_7N_2O_2$$ for an experiment. How many moles should they weigh out? (Molar mass = 113.10 g/mol)

Accepted Answer

$$\dfrac{50.0}{113.10} = 0.442\ \mathrm{mol}$$

Molar Mass: Calculation and Applications in GOB Chemistry

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