Q: Which of the following is the correct formula for calculating percent composition by mass of an element in a compound?

$$\frac{\text{mass of element in 1 mol of compound}}{\text{molar mass of compound}} \times 100$$

Q: Which of the following is the correct formula for calculating the number of moles from mass and molar mass?

$$n = \frac{\text{mass}}{\text{molar mass}}$$

Q: Which of the following is the correct formula for calculating percent yield?

$$\frac{\text{actual yield}}{\text{theoretical yield}} \times 100$$

Question 1

Which of the following best describes the difference between an empirical formula and a molecular formula?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms in a compound, while the molecular formula shows the actual number of atoms in a molecule.

Question 2

A sample contains 0.50 mol of NaCl. How many formula units of NaCl are present in the sample? Use $$N_A = 6.022 	imes 10$$^{23}$$ mol$$^{-1}$$.

Accepted Answer

$$3.01 	imes 10$$^{23}$$

Question 3

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

Accepted Answer

$$\frac{	ext{mass of element in 1 mol of compound}}{	ext{molar mass of compound}} 	imes 100$$

Question 4

A compound contains 40.0% C, 6.7% H, and 53.3% O by mass. What is the empirical formula of the compound?

Accepted Answer

CH$$_2O$$

Question 5

Which of the following is a correct statement about limiting reactants in a chemical reaction?

Accepted Answer

The limiting reactant determines the maximum amount of product that can be formed.

Question 6

Given the reaction: $$2H_2 + O_2$ \rightarrow 2H_2O$$, if you start with 4 mol of $$H_2$$ and 2 mol of $$O_2$$, what is the limiting reactant?

Accepted Answer

Neither, both are in exact stoichiometric ratio

Question 7

A student mixes 10.0 g of $$Al$$ with 35.0 g of $$Cl_2 to $$produce $$AlCl_3. $$Which reactant is limiting? (Molar masses: $$Al = 26.98 g/$$mol, $$Cl_2 = 70.90$ g/mol)

Accepted Answer

$$Al$$

Question 8

Which equation correctly relates molarity ($$M$$), moles of solute ($$n$$), and volume of solution ($$V in L$$)?

Accepted Answer

$$M = \frac{n}{V}$$

Question 9

What is the molarity of a solution prepared by dissolving 5.00 g of $$NaCl ($$molar mass = 58.44 g/mol) in enough water to make 250.0 mL of solution?

Accepted Answer

$$0.342 M$$

Question 10

Which of the following is the correct net ionic equation for the reaction between $$AgNO_3$$ and $$NaCl in $$aqueous solution?

Accepted Answer

$$Ag^+ (aq) + Cl^- (aq) \rightarrow AgCl (s)$$

Question 11

Which of the following is a strong electrolyte in aqueous solution?

Accepted Answer

$$NaCl$$

Question 12

Which of the following is the correct formula for the dilution equation?

Accepted Answer

$$M_1V_1 = M_2V_2$$

Question 13

A solution is prepared by diluting 50.0 mL of 2.00 M $$HCl to a $$final volume of 250.0 mL. What is the final concentration?

Accepted Answer

$$0.400 M$$

Question 14

Which of the following is a correct statement about spectator ions?

Accepted Answer

Spectator ions remain unchanged and do not participate in the reaction.

Question 15

Which of the following is the correct formula for calculating the number of moles from mass and molar mass?

Accepted Answer

$$n = \frac{	ext{mass}}{	ext{molar mass}}$$

Question 16

A reaction produces 15.0 g of $$CO_2$$ from 10.0 g of $$C_2H_5OH. $$What is the percent yield if the theoretical yield is 20.0 g?

Accepted Answer

$$75\%$$

Question 17

Which of the following is the correct formula for calculating percent yield?

Accepted Answer

$$\frac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100$$

Question 18

Which of the following is a correct statement about the solubility rules for ionic compounds in water?

Accepted Answer

All nitrates ($$NO_3$$^-$$) are soluble in water.

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