Question

chemistry 2202 assignment e
name: claire healey
answer each of the questions below. include the formula that you are using, units and significant digits. note: full marks will only be given when formula, units and significant digits are shown.

1. calculate the number of moles in 5.56 x 10^24 atoms of sodium sulfate.

step1
info

1. calculate the number of moles present in 14.6 grams of ammonium phosphate.
2. how many moles are in 49.7 l of oxygen gas at stp?

Explanation:

Step1: Recall Avogadro's number for first - question

The formula to convert the number of atoms/molecules to moles is $n=\frac{N}{N_A}$, where $n$ is the number of moles, $N$ is the number of atoms/molecules, and $N_A = 6.022\times10^{23}\text{ atoms/mol}$. For sodium sulfate ($Na_2SO_4$), $N = 5.56\times 10^{24}$ atoms.
$n_1=\frac{5.56\times 10^{24}}{6.022\times 10^{23}}$

Step2: Calculate molar mass for second - question

The molar mass of ammonium phosphate $(NH_4)_3PO_4$:

• $M_{N}=14.01\text{ g/mol}$, $M_{H}=1.01\text{ g/mol}$, $M_{P}=30.97\text{ g/mol}$, $M_{O}=16.00\text{ g/mol}$
• $M=(3\times14.01)+(12\times1.01)+30.97+(4\times16.00)=149.12\text{ g/mol}$

The formula to convert mass to moles is $n=\frac{m}{M}$, where $m = 14.6\text{ g}$ and $M = 149.12\text{ g/mol}$. So $n_2=\frac{14.6}{149.12}$

Step3: Recall molar volume at STP for third - question

At standard temperature and pressure (STP), the molar volume of a gas is $V_m = 22.4\text{ L/mol}$. The formula to convert volume of gas at STP to moles is $n=\frac{V}{V_m}$, where $V = 49.7\text{ L}$ and $V_m=22.4\text{ L/mol}$. So $n_3=\frac{49.7}{22.4}$

Answer:

1. $n_1=\frac{5.56\times 10^{24}}{6.022\times 10^{23}}\approx9.23\text{ mol}$
2. $n_2=\frac{14.6}{149.12}\approx0.0979\text{ mol}$
3. $n_3=\frac{49.7}{22.4}\approx2.22\text{ mol}$