Q: Which of the following statements about Avogadro's number is correct?

It is the number of particles in one mole, equal to $$6.02 \times 10$$^{23}$$.

Question 1

Which of the following best describes why coefficients, rather than subscripts, are changed when balancing chemical equations?

Accepted Answer

Changing coefficients alters the number of molecules, preserving the identity of the substances.

Question 2

A sample of glucose ($$C_6H_{12}O_6$) weighing 18.0 g is completely combusted in oxygen. How many grams of CO_2$ are produced? (Molar masses: C_6H$$_{12}$$O_6 = 180.0$ g/mol, CO_2$ = 44.0 g/$$mol)

Accepted Answer

$$26.4 g$$

Question 3

Which of the following is the correct balanced equation for the reaction of aluminum hydroxide with hydrochloric acid?

Accepted Answer

$$Al(OH)_3(s) + 3HCl(aq) \rightarrow $$AlCl_3$$(aq) + 3H_2O(l)$$

Question 4

A 0.1005 g sample of menthol is combusted, producing 0.2829 g of $$CO_2$$ and 0.1159 g of $$H_2O. If $$menthol contains only C, H, and O, what is the empirical formula of menthol?

Accepted Answer

$$C_{10}H$$_{18}$$O$

Question 5

Which of the following is a decomposition reaction?

Accepted Answer

$$2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$$

Question 6

A compound has an empirical formula of $$CH_2O$$ and a molar mass of 180 g/mol. What is its molecular formula?

Accepted Answer

$$C_6H_{12}O_6$

Question 7

Which of the following best describes a combustion reaction?

Accepted Answer

A reaction in which a substance reacts rapidly with oxygen, producing heat and light.

Question 8

What is the percent by mass of oxygen in sulfuric acid ($$H_2SO_4$$)? (Atomic masses: H = 1.0, S = 32.1, O = 16.0)

Accepted Answer

$$65.0\%$$

Question 9

If 30.0 g of benzene ($$C_6H_6) $$reacts with 65.0 g of bromine ($$Br_2) to $$form bromobenzene ($$C_6H_5Br$$), what is the theoretical yield of bromobenzene? (Molar masses: $$C_6H_6 = 78.0 g/$$mol, $$Br_2 = 160.0$ g/mol, C_6H_5Br = 157.0$ g/mol)

Accepted Answer

$$47.6 g$$

Question 10

A sample contains 69.0% C, 8.80% H, and 15.51% O by mass and has a molar mass of 206 g/mol. What is the molecular formula of the compound?

Accepted Answer

$$C_{13}H$$_{18}$$O_2$$

Question 11

Which of the following statements about Avogadro's number is correct?

Accepted Answer

It is the number of particles in one mole, equal to $$6.02 	imes 10$$^{23}$$.

Question 12

A 1.00 g sample of sodium bicarbonate ($$NaHCO_3) $$reacts with 1.00 g of citric acid ($$H_3C_6H_5O_7) $$according to the equation: $$3NaHCO_3(aq) + H_3C_6H_5O_7(aq) \rightarrow 3CO_2(g) + 3H_2O(l) + Na_3C_6H_5O_7(aq). $$Which is the limiting reactant?

Accepted Answer

Citric acid ($$H_3C_6H_5O_7)$$

Question 13

What is the percent yield if the actual yield of bromobenzene ($$C_6H_5Br) is 42.3 g $$and the theoretical yield is 47.6 g?

Accepted Answer

$$89.1\%$$

Question 14

Which of the following is the correct formula for the product of a combination reaction between magnesium and nitrogen?

Accepted Answer

$$Mg_3N_2$$

Question 15

How many molecules are present in 11.00 mg of aspartame ($$C_{14}H$$_{18}$$N_2O_5$, molar mass = 294 g/mol)?

Accepted Answer

$$2.25 	imes 10$$^{19}$$

Question 16

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

Accepted Answer

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

Question 17

A sample of calcium hydride ($$CaH_2) $$reacts with water to form calcium hydroxide and hydrogen gas. If you want to produce 4.500 g of hydrogen gas, how many grams of $$CaH_2$$ are needed? (Molar masses: $$CaH_2 = 42.1$ g/mol, H_2$ = 2.0 g/$$mol)

Accepted Answer

$$47.3 g$$

Question 18

Which of the following is the correct percent composition by mass of carbon in glucose ($$C_6H_{12}O_6$)? (Molar mass: C_6H$$_{12}$$O_6 = 180.0$ g/mol)

Accepted Answer

$$40.0\%$$

Question 19

Which of the following is the correct sequence of steps to determine the empirical formula from percent composition?

Accepted Answer

Convert percent to grams, convert grams to moles, divide by smallest number of moles.

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