$$\frac{55.85}{55.85} \times 6.022 \times 10$$^{23}$$ atoms

$$\text{Mass (g)} = \text{Moles} \times \text{Molar Mass (g/mol)}$$

$$\frac{41.6}{96.09} \times 6.022 \times 10$$^{23}$$ formula units

$$10.0 \times \frac{3}{2}$$ mol

$$1.75 \times 0.460 \times 141.96 g$$

$$\frac{51.4}{66.73} \times 100$$

Question 1

Which statement best describes the concept of the mole in chemistry?

Accepted Answer

A mole is the amount of a substance that contains Avogadro's number ($$6.022 	imes 10$$^{23}$$) of entities.

Question 2

If you have 55.85 grams of iron (Fe), how many atoms of iron do you have?

Accepted Answer

$$\frac{55.85}{55.85} 	imes 6.022 	imes 10$$^{23}$$ atoms

Question 3

Which equation correctly relates mass, moles, and molar mass?

Accepted Answer

$$	ext{Mass (g)} = 	ext{Moles} 	imes 	ext{Molar Mass (g/mol)}$$

Question 4

A sample contains $$0.0342$$ mol of silver (Ag). What is the mass of silver in the sample?

Accepted Answer

$$0.0342 	imes 107.9 g$$

Question 5

How many formula units of ammonium carbonate ($$(NH_4$)_2CO_3) $$are in $$41.6 g of $$the compound? (Molar mass = $$96.09 g/$$mol)

Accepted Answer

$$\frac{41.6}{96.09} 	imes 6.022 	imes 10$$^{23}$$ formula units

Question 6

What is the empirical formula for a compound containing $$2.82 g Na$$, $$4.35 g Cl$$, and $$7.83 g O$$?

Accepted Answer

NaClO$$_4$$

Question 7

A compound contains $$40.0$$% C, $$6.71$$% H, and $$53.3$$% O by mass. Its molar mass is $$90.08 g/$$mol. What is its molecular formula?

Accepted Answer

C$$_3H$_6O$_3$$

Question 8

Which of the following is NOT a correct step in balancing a chemical equation?

Accepted Answer

Change the subscripts of compounds to balance atoms.

Question 9

In the reaction $$2Cu_2S(s) + 3O_2(g) \rightarrow 2Cu_2O(s) + 2SO_2(g)$$, how many moles of $$O_2$$ are required to roast $$10.0$$ mol of $$Cu_2S$$?

Accepted Answer

$$10.0 	imes \frac{3}{2}$$ mol

Question 10

A solution contains $$0.715$$ mol of glycine in $$495 mL. $$What is the molarity of the solution?

Accepted Answer

$$\frac{0.715}{0.495 \div 1000} M$$

Question 11

How many grams of sodium monohydrogen phosphate ($$Na_2HPO_4$$, molar mass $$141.96 g/$$mol) are in $$1.75 L of$$ $$0.460 M $$solution?

Accepted Answer

$$1.75 	imes 0.460 	imes 141.96 g$$

Question 12

What is the percent yield if $$100.0 kg of$$ $$SiO_2$$ produces $$51.4 kg of$$ $$SiC$$? (Theoretical yield = $$66.73 kg)$$

Accepted Answer

$$\frac{51.4}{66.73} 	imes 100$$

Question 13

Which of the following best describes the relationship between empirical and molecular formulas?

Accepted Answer

The molecular formula is a whole-number multiple of the empirical formula.

Question 14

A tablet contains $$0.10 g of$$ $$Mg(OH)_2. $$How many liters of $$0.10 M$$ $$HCl$$ are needed to neutralize it?

Accepted Answer

$$\frac{0.10}{58.33} 	imes 2 \div 0.10 L$$

Question 15

Which of the following is a correct formula for calculating mass percent of an element X in a compound?

Accepted Answer

$$\frac{	ext{atoms of X in formula} 	imes 	ext{atomic mass of X}}{	ext{molecular mass of compound}} 	imes 100$$

Question 16

Which of the following is true about Avogadro's number?

Accepted Answer

It is the number of entities in 1 mole of a substance.

Question 17

A solution is prepared by diluting $$0.12$$ mol NaCl from a $$6.0 M $$stock solution to $$0.80 L. $$What volume of stock solution is required?

Accepted Answer

$$\frac{0.12}{6.0} L$$

Stoichiometry of Formulas and Equations: The Mole, Mass Relationships, and Chemical Calculations

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