Question

1. what is the % of each element in ni₃(po₄)₂?
2. what is the % of each element in al₂(cro₄)₃?
3. what is the % of each element in (nh₄)₂(so₄)?

Explanation:

Problem 4: $\text{Ni}_3(\text{PO}_4)_2$

Step1: Calculate molar mass

First, find atomic masses: $\text{Ni}=58.69\ \text{g/mol}$, $\text{P}=30.97\ \text{g/mol}$, $\text{O}=16.00\ \text{g/mol}$
Molar mass:
$$3\times58.69 + 2\times(30.97 + 4\times16.00) = 176.07 + 2\times(94.97) = 176.07 + 189.94 = 366.01\ \text{g/mol}$$

Step2: Find % of Ni

$$\% \text{Ni} = \frac{3\times58.69}{366.01} \times 100\% = \frac{176.07}{366.01} \times 100\% \approx 48.11\%$$

Step3: Find % of P

$$\% \text{P} = \frac{2\times30.97}{366.01} \times 100\% = \frac{61.94}{366.01} \times 100\% \approx 16.92\%$$

Step4: Find % of O

$$\% \text{O} = \frac{8\times16.00}{366.01} \times 100\% = \frac{128.00}{366.01} \times 100\% \approx 34.97\%$$

Step1: Calculate molar mass

Atomic masses: $\text{Al}=26.98\ \text{g/mol}$, $\text{Cr}=52.00\ \text{g/mol}$, $\text{O}=16.00\ \text{g/mol}$
Molar mass:
$$2\times26.98 + 3\times(52.00 + 4\times16.00) = 53.96 + 3\times(116.00) = 53.96 + 348.00 = 401.96\ \text{g/mol}$$

Step2: Find % of Al

$$\% \text{Al} = \frac{2\times26.98}{401.96} \times 100\% = \frac{53.96}{401.96} \times 100\% \approx 13.42\%$$

Step3: Find % of Cr

$$\% \text{Cr} = \frac{3\times52.00}{401.96} \times 100\% = \frac{156.00}{401.96} \times 100\% \approx 38.81\%$$

Step4: Find % of O

$$\% \text{O} = \frac{12\times16.00}{401.96} \times 100\% = \frac{192.00}{401.96} \times 100\% \approx 47.77\%$$

Step1: Calculate molar mass

Atomic masses: $\text{N}=14.01\ \text{g/mol}$, $\text{H}=1.008\ \text{g/mol}$, $\text{S}=32.07\ \text{g/mol}$, $\text{O}=16.00\ \text{g/mol}$
Molar mass:
$$2\times(14.01 + 4\times1.008) + 32.07 + 4\times16.00 = 2\times(18.042) + 32.07 + 64.00 = 36.084 + 96.07 = 132.154\ \text{g/mol}$$

Step2: Find % of N

$$\% \text{N} = \frac{2\times14.01}{132.154} \times 100\% = \frac{28.02}{132.154} \times 100\% \approx 21.20\%$$

Step3: Find % of H

$$\% \text{H} = \frac{8\times1.008}{132.154} \times 100\% = \frac{8.064}{132.154} \times 100\% \approx 6.10\%$$

Step4: Find % of S

$$\% \text{S} = \frac{32.07}{132.154} \times 100\% \approx 24.27\%$$

Step5: Find % of O

$$\% \text{O} = \frac{4\times16.00}{132.154} \times 100\% = \frac{64.00}{132.154} \times 100\% \approx 48.43\%$$

Answer:

$\text{Ni}: 48.11\%$, $\text{P}: 16.92\%$, $\text{O}: 34.97\%$

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Problem 5: $\text{Al}_2(\text{CrO}_4)_3$