Question

practice problems

1. a. 9.03 g mg combine completely with 3.48 g n to form a compound. what is the percent composition of this compound?

b. 29.0 g ag combine completely with 4.30 g s to form a compound. what is the percent composition of this compound?

1. when a 14.2-g sample of mercury(ii) oxide is decomposed into its elements by heating, 13.2 g hg is obtained. what is the percent composition of this compound?

Explanation:

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Part 29a

Step1: Calculate total mass

$\text{Total mass} = 9.03\ \text{g} + 3.48\ \text{g} = 12.51\ \text{g}$

Step2: % of Mg by mass

$\% \text{Mg} = \frac{9.03}{12.51} \times 100 = 72.2\%$

Step3: % of N by mass

$\% \text{N} = \frac{3.48}{12.51} \times 100 = 27.8\%$

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Part 29b

Step1: Calculate total mass

$\text{Total mass} = 29.0\ \text{g} + 4.30\ \text{g} = 33.3\ \text{g}$

Step2: % of Ag by mass

$\% \text{Ag} = \frac{29.0}{33.3} \times 100 = 87.1\%$

Step3: % of S by mass

$\% \text{S} = \frac{4.30}{33.3} \times 100 = 12.9\%$

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Problem 30

Step1: Find mass of oxygen

$\text{Mass of O} = 14.2\ \text{g} - 13.2\ \text{g} = 1.0\ \text{g}$

Step2: % of Hg by mass

$\% \text{Hg} = \frac{13.2}{14.2} \times 100 = 92.96\% \approx 93.0\%$

Step3: % of O by mass

$\% \text{O} = \frac{1.0}{14.2} \times 100 = 7.04\% \approx 7.0\%$

Answer:

29a. 72.2% Mg, 27.8% N
29b. 87.1% Ag, 12.9% S

1. 93.0% Hg, 7.0% O