Question

chemistry 11 - unit 3: mole concept
for all questions, show your work, correct sig. figs and units where applicable.

1. what is the molar mass of nickel (iii) sulfate?
2. what is the percent composition by mass of hydrogen in (nh₄)₃po₄?
3. what is the mass of 8.19 x 10²⁵ molecules of carbon monoxide?
4. what is the mass of 7.59 mmol of mg(clo₂)₂?

Explanation:

Step1: Determine the molar mass of Nickel (III) sulfate

Nickel (III) sulfate has the formula $Ni_2(SO_4)_3$. The molar mass of $Ni$ is approximately 58.69 g/mol, $S$ is approximately 32.07 g/mol and $O$ is approximately 16.00 g/mol.

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Step2: Calculate the percent - composition by mass of hydrogen in $(NH_4)_3PO_4$

The molar mass of $(NH_4)_3PO_4$:
$M_{(NH_4)_3PO_4}=3\times(14.01 + 4\times1.01)+30.97+4\times16.00$
$=3\times(14.01+4.04)+30.97 + 64.00$
$=3\times18.05+30.97+64.00$
$=54.15+30.97+64.00$
$=149.12\space g/mol$
The molar mass contributed by hydrogen is $3\times4\times1.01 = 12.12\space g/mol$.
The percent - composition of hydrogen is $\frac{12.12}{149.12}\times100\%\approx8.13\%$

Step3: Find the mass of $8.19\times10^{25}$ molecules of carbon monoxide

First, use Avogadro's number $N_A = 6.022\times10^{23}\space mol^{-1}$ to find the number of moles.
$n=\frac{N}{N_A}=\frac{8.19\times10^{25}}{6.022\times10^{23}} = 136.0\space mol$
The molar mass of $CO$ is $M_{CO}=12.01 + 16.00=28.01\space g/mol$
The mass $m=n\times M=136.0\times28.01 = 3830\space g$

Step4: Calculate the mass of $7.59\space mmol$ of $Mg(ClO_2)_2$

First, convert millimoles to moles: $n = 7.59\times10^{-3}\space mol$
The molar mass of $Mg(ClO_2)_2$:
$M_{Mg(ClO_2)_2}=24.31+2\times(35.45 + 2\times16.00)$
$=24.31+2\times(35.45 + 32.00)$
$=24.31+2\times67.45$
$=24.31+134.9$
$=159.21\space g/mol$
The mass $m=n\times M=7.59\times10^{-3}\times159.21\approx1.21\space g$

Answer:

1. The molar mass of Nickel (III) sulfate is $405.59\space g/mol$.
2. The percent - composition by mass of hydrogen in $(NH_4)_3PO_4$ is approximately $8.13\%$.
3. The mass of $8.19\times10^{25}$ molecules of carbon monoxide is $3830\space g$.
4. The mass of $7.59\space mmol$ of $Mg(ClO_2)_2$ is approximately $1.21\space g$.