Q: How many oxygen atoms are present in 2.5 moles of Fe2(SO4)3?

$$2.5 \times 12 \times 6.022 \times 10$$^{23}$$

Q: A 0.45 gram sample of aspirin is decomposed and found to contain 0.27 g C, 0.020 g H, and 0.16 g O. What is the mass percent of hydrogen in aspirin?

$$\frac{0.020}{0.45} \times 100 = 4.44\%$$

Q: How many atoms are present in 26.1 grams of iron? (Molar mass of Fe = 55.85 g/mol, Avogadro's number $$= 6.022 \times 10$$^{23}$$)

$$\frac{26.1}{55.85} \times 6.022 \times 10$$^{23}$$

Question 1

A sample of carbon tetrachloride contains 47.2 grams of chlorine. Given that the chlorine-to-carbon mass ratio in carbon tetrachloride is 11.8:1, what is the mass of carbon in the sample?

Accepted Answer

4.0 g

Question 2

Which of the following best describes the law of constant composition as it applies to sodium chloride (NaCl)?

Accepted Answer

The ratio of sodium to chlorine by mass is always the same in any sample of NaCl.

Question 3

How many oxygen atoms are present in 2.5 moles of Fe2(SO4)3?

Accepted Answer

$$2.5 	imes 12 	imes 6.022 	imes 10$$^{23}$$

Question 4

Which of the following compounds is most likely to be soluble in water?

Accepted Answer

CuCl2

Question 5

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

Accepted Answer

CH2O

Question 6

Which of the following is a molecular element?

Accepted Answer

Iodine

Question 7

How many moles of oxygen atoms are present in 3.0 moles of Ca(NO3)2?

Accepted Answer

12.0 mol

Question 8

A 0.45 gram sample of aspirin is decomposed and found to contain 0.27 g C, 0.020 g H, and 0.16 g O. What is the mass percent of hydrogen in aspirin?

Accepted Answer

$$\frac{0.020}{0.45} 	imes 100 = 4.44\%$$

Question 9

Which of the following best describes what happens when water boils in a pot?

Accepted Answer

A physical change occurs, as water changes from liquid to gas.

Question 10

Which of the following sets of reactants will form a solid precipitate when mixed?

Accepted Answer

Na2CO3 (aq) & CaCl2 (aq)

Question 11

A sample of pure silver has a mass of 310 grams. How many moles of silver are in the sample? (Molar mass of Ag = 107.87 g/mol)

Accepted Answer

$$\frac{310}{107.87} = 2.87$$ mol

Question 12

Which compound has the highest mass percent of carbon?

Accepted Answer

CO

Question 13

What is the correct set of coefficients to balance the following equation: $$\mathrm{C_6H_6 (l) + O_2$ (g) \rightarrow CO_2$ (g) + H_2O (l)}$$?

Accepted Answer

2, 15, 12, 6

Question 14

A compound has the empirical formula CH2O and a molar mass of 180.16 g/mol. What is its molecular formula?

Accepted Answer

C6H12O6

Question 15

How many atoms are present in 26.1 grams of iron? (Molar mass of Fe = 55.85 g/mol, Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$\frac{26.1}{55.85} 	imes 6.022 	imes 10$$^{23}$$

Question 16

Which of the following is an example of a chemical reaction?

Accepted Answer

Iron rusting when left outside

Question 17

What is the mass percent of nitrogen in C2H8N2? (Molar mass: C = 12.01, H = 1.01, N = 14.01)

Accepted Answer

46.6%

Question 18

Which of the following compounds is classified as an ionic compound?

Accepted Answer

MgSO4

Question 19

A compound is decomposed in the laboratory and produces 2.10 g of N and 0.30 g of H. What is the empirical formula?

Accepted Answer

NH2

Chemistry 4 Exam 2 Review – Step-by-Step Study Guidance

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