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

One mole of any substance contains $$6.02 \times 10$$^{23}$$ particles.

Question 1

Which of the following best explains why we balance chemical equations by changing coefficients rather than subscripts?

Accepted Answer

Changing subscripts would alter the identity of the substances involved in the reaction.

Question 2

A sample of glucose ($$C_6H_{12}O_6$) weighing 18.0 g is completely combusted in excess oxygen. How many grams of CO_2$ are produced? (Molar mass of C_6H$$_{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 combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

$$CH_4(g) + 2O_2(g$$) \rightarrow $$CO_2(g) + 2H_2O(g$$)$$

Question 4

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

Accepted Answer

$$CH_2O$$

Question 5

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

Accepted Answer

One mole of any substance contains $$6.02 	imes 10$$^{23}$$ particles.

Question 6

A 10.0 g sample of calcium carbonate ($$CaCO_3) is $$heated strongly. What mass of $$CO_2 (g) is $$released? (Molar mass: $$CaCO_3 = 100.0$ g/mol, CO_2$ = 44.0 g/$$mol)

Accepted Answer

$$4.4 g$$

Question 7

Which of the following is a decomposition reaction?

Accepted Answer

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

Question 8

If 5.00 g of $$H_2$$ reacts with 10.0 g of $$O_2 to $$form water, which is the limiting reactant? (Molar masses: $$H_2 = 2.0$ g/mol, O_2$ = 32.0 g/$$mol)

Accepted Answer

$$O_2$$

Question 9

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

$$72\%$$

Question 10

Which of the following best describes a combustion reaction?

Accepted Answer

A reaction in which a substance reacts rapidly with oxygen, producing a flame.

Question 11

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

Accepted Answer

$$2.04\%$$

Question 12

A compound has an empirical formula of $$CH_2$$ and a molar mass of 56 g/mol. What is its molecular formula?

Accepted Answer

$$C_4H_8$$

Question 13

Which of the following is the correct formula weight (in amu) for $$Al_2$$($$SO_4)_3$? (Atomic masses: Al = 27.0, S = 32.1, O = 16.0)

Accepted Answer

$$342.2$$ amu

Question 14

In a combustion analysis, a 0.500 g sample of a compound containing only C, H, and O produces 1.10 g $$CO_2$$ and 0.450 g $$H_2O. $$What is the mass of oxygen in the original sample?

Accepted Answer

$$0.090 g$$

Question 15

Which of the following is a combination reaction?

Accepted Answer

$$2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)$$

Question 16

How many molecules are present in 0.25 mol of $$CO_2$$?

Accepted Answer

$$1.51 	imes 10$$^{23}$$

Question 17

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

Accepted Answer

It determines the maximum amount of product that can be formed.

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