Q: A chemist isolates 0.250 mol of glucose (C$$_6H$_{12}O$_6). $$What is the mass of this sample in grams? (Molar mass of glucose = 180.16 g/mol)

$$0.250 \times 180.16 = 45.04 g$$

Q: Which of the following statements about the mole is correct?

A mole contains $$6.022 \times 10$$^{23}$$ entities, regardless of the substance.

Q: A sample contains 3.01 $$\times 10$^{23}$$ molecules of water (H$$_2O). $$How many moles of water are present?

$$\frac{3.01 \times 10$$^{23}$$}{6.022 \times 10$$^{23}$$} = 0.500$$ mol

Q: Which of the following best describes the relationship between molar mass and the number of moles?

Number of moles = $$\frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$$

Q: If 10.0 g of sulfur (S) reacts with excess oxygen to form SO$$_2$$, how many grams of SO$$_2$$ are produced? (Molar mass S = 32.06 g/mol, SO$$_2 = 64.07 g/$$mol)

$$10.0 \text{ g S} \times \frac{1 \text{ mol S}}{32.06 \text{ g S}} \times \frac{1 \text{ mol SO}_2}{1 \text{ mol S}} \times \frac{64.07 \text{ g SO}_2}{1 \text{ mol SO}_2} = 20.0 g$$

Q: A reaction has a theoretical yield of 25.0 g, but only 18.0 g of product is actually obtained. What is the percent yield?

$$\frac{18.0}{25.0} \times 100\% = 72.0\%$$

Q: Which of the following is the correct molar mass of sulfuric acid (H$$_2SO$_4$$)? (Atomic masses: H = 1.01, S = 32.07, O = 16.00)

$$2 \times 1.01 + 32.07 + 4 \times 16.00 = 98.09 g/$$mol

Question 1

A chemist isolates 0.250 mol of glucose (C$$_6H$_{12}O$_6). $$What is the mass of this sample in grams? (Molar mass of glucose = 180.16 g/mol)

Accepted Answer

$$0.250 	imes 180.16 = 45.04 g$$

Question 2

Which of the following statements about the mole is correct?

Accepted Answer

A mole contains $$6.022 	imes 10$$^{23}$$ entities, regardless of the substance.

Question 3

A sample contains 3.01 $$	imes 10$^{23}$$ molecules of water (H$$_2O). $$How many moles of water are present?

Accepted Answer

$$\frac{3.01 	imes 10$$^{23}$$}{6.022 	imes 10$$^{23}$$} = 0.500$$ mol

Question 4

Which of the following best describes the relationship between molar mass and the number of moles?

Accepted Answer

Number of moles = $$\frac{	ext{mass (g)}}{	ext{molar mass (g/mol)}}$$

Question 5

A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

CH$$_2O$$

Question 6

If 10.0 g of sulfur (S) reacts with excess oxygen to form SO$$_2$$, how many grams of SO$$_2$$ are produced? (Molar mass S = 32.06 g/mol, SO$$_2 = 64.07 g/$$mol)

Accepted Answer

$$10.0 	ext{ g S} 	imes \frac{1 	ext{ mol S}}{32.06 	ext{ g S}} 	imes \frac{1 	ext{ mol SO}_2}{1 	ext{ mol S}} 	imes \frac{64.07 	ext{ g SO}_2}{1 	ext{ mol SO}_2} = 20.0 g$$

Question 7

Which of the following is the correct balanced chemical equation for the combustion of glucose (C$$_6H$_{12}O$_6$$)?

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\ \mathrm{O}_2 \rightarrow 6\ \mathrm{CO}_2 + 6\ \mathrm{H}_2\mathrm{O}$$

Question 8

A 5.00 g sample of NaCl is dissolved in water. How many moles of NaCl are present? (Molar mass NaCl = 58.44 g/mol)

Accepted Answer

$$\frac{5.00}{58.44} = 0.0856$$ mol

Question 9

Which of the following best describes a limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed first, thus limiting the amount of product formed.

Question 10

A reaction has a theoretical yield of 25.0 g, but only 18.0 g of product is actually obtained. What is the percent yield?

Accepted Answer

$$\frac{18.0}{25.0} 	imes 100\% = 72.0\%$$

Question 11

Which of the following is the correct molar mass of sulfuric acid (H$$_2SO$_4$$)? (Atomic masses: H = 1.01, S = 32.07, O = 16.00)

Accepted Answer

$$2 	imes 1.01 + 32.07 + 4 	imes 16.00 = 98.09 g/$$mol

Question 12

A sample of a compound contains 0.100 mol of C, 0.200 mol of H, and 0.100 mol of O. What is the empirical formula?

Accepted Answer

CH$$_2O$$

Question 13

Which of the following best explains why the mole is a useful unit in chemistry?

Accepted Answer

It allows chemists to count atoms, molecules, or ions by weighing macroscopic amounts of material.

Question 14

How many oxygen atoms are present in 2.00 mol of glucose (C$$_6H$_{12}O$_6$$)?

Accepted Answer

$$2.00 	ext{ mol} 	imes 6.022 	imes 10$$^{23}$$ 	ext{ molecules/mol} 	imes 6 = 7.23 	imes 10$$^{24}$$ atoms

Question 15

A student needs to prepare 0.500 mol of NaOH solution. What mass of NaOH is required? (Molar mass NaOH = 40.00 g/mol)

Accepted Answer

$$0.500 	imes 40.00 = 20.0 g$$

Question 16

Which of the following is NOT a step in determining the empirical formula from percent composition?

Accepted Answer

Adding the percent composition values together to get the formula

Question 17

A reaction requires 2.00 mol of H$$_2$$ and 1.00 mol of O$$_2 to $$produce water. If you have 2.00 mol of H$$_2$$ and 0.50 mol of O$$_2$$, what is the limiting reactant?

Accepted Answer

O$$_2$$

Question 18

Which of the following best describes the law of conservation of mass as it applies to chemical equations?

Accepted Answer

The total mass of reactants equals the total mass of products in a balanced chemical equation.

Question 19

A 10.0 g sample of CaCO$$_3 ($$molar mass = 100.09 g/mol) is decomposed by heating. How many moles of CO$$_2$$ are produced?

Accepted Answer

$$\frac{10.0}{100.09} = 0.100$$ mol

Stoichiometry of Formulas and Equations: Study Notes

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