Question

1. how many grams are in 2.5 moles of oxygen gas ($o_2$)?

a. 40 g
b. 80 g
c. 16 g
d. 32 g

1. how many moles are in 44.0 g of carbon dioxide ($co_2$)?

a. 0.50 mol
b. 1.00 mol
c. 2.00 mol
d. 4.00 mol

1. how many molecules are in 2.00 moles of water ($h_2o$)?

a. $6.02 \times 10^{23}$
b. $1.20 \times 10^{24}$
c. $3.01 \times 10^{23}$
d. $2.00 \times 10^{23}$

Explanation:

Step1: Find molar mass of $\text{O}_2$

Molar mass of $\text{O}$ = $16\ \text{g/mol}$, so $\text{O}_2$: $2 \times 16 = 32\ \text{g/mol}$

Step2: Calculate mass of $\text{O}_2$

$\text{Mass} = \text{Moles} \times \text{Molar Mass} = 2.5\ \text{mol} \times 32\ \text{g/mol} = 80\ \text{g}$

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Step1: Find molar mass of $\text{CO}_2$

Molar mass of $\text{C}=12\ \text{g/mol}$, $\text{O}=16\ \text{g/mol}$, so $\text{CO}_2$: $12 + 2\times16 = 44\ \text{g/mol}$

Step2: Calculate moles of $\text{CO}_2$

$\text{Moles} = \frac{\text{Mass}}{\text{Molar Mass}} = \frac{44.0\ \text{g}}{44\ \text{g/mol}} = 1.00\ \text{mol}$

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Step1: Use Avogadro's number

Avogadro's number $N_A = 6.02 \times 10^{23}\ \text{molecules/mol}$

Step2: Calculate number of molecules

$\text{Molecules} = \text{Moles} \times N_A = 2.00\ \text{mol} \times 6.02 \times 10^{23}\ \text{molecules/mol} = 1.204 \times 10^{24} \approx 1.20 \times 10^{24}$

Answer:

1. B. 80 g
2. B. 1.00 mol
3. B. $1.20 \times 10^{24}$