Question

instructions: show all work and include units in every step.

1. how many moles are in 18.0 g of h₂o?
2. how many moles are in 44.0 g of co₂?
3. how many moles are in 58.5 g of nacl?
4. how many moles are in 84.0 g of nahco₃?
5. what is the mass (in grams) of 0.750 mol of nh₃?
6. what is the mass (in grams) of 1.25 mol of cacl₂?
7. what is the mass (in grams) of 2.00 mol of co₂?
8. what is the mass (in grams) of 0.500 mol of na₂so₄?

Explanation:

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

Molar mass of $\text{H}_2\text{O} = (2\times1.008) + 16.00 = 18.016\ \text{g/mol}$

Step2: Moles of $\text{H}_2\text{O}$: mass/molar mass

$\text{Moles} = \frac{18.0\ \text{g}}{18.016\ \text{g/mol}} \approx 1.00\ \text{mol}$

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

Molar mass of $\text{CO}_2 = 12.01 + (2\times16.00) = 44.01\ \text{g/mol}$

Step2: Moles of $\text{CO}_2$: mass/molar mass

$\text{Moles} = \frac{44.0\ \text{g}}{44.01\ \text{g/mol}} \approx 1.00\ \text{mol}$

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Step1: Calculate molar mass of $\text{NaCl}$

Molar mass of $\text{NaCl} = 22.99 + 35.45 = 58.44\ \text{g/mol}$

Step2: Moles of $\text{NaCl}$: mass/molar mass

$\text{Moles} = \frac{58.5\ \text{g}}{58.44\ \text{g/mol}} \approx 1.00\ \text{mol}$

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Step1: Calculate molar mass of $\text{NaHCO}_3$

Molar mass of $\text{NaHCO}_3 = 22.99 + 1.008 + 12.01 + (3\times16.00) = 84.008\ \text{g/mol}$

Step2: Moles of $\text{NaHCO}_3$: mass/molar mass

$\text{Moles} = \frac{84.0\ \text{g}}{84.008\ \text{g/mol}} \approx 1.00\ \text{mol}$

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Step1: Calculate molar mass of $\text{NH}_3$

Molar mass of $\text{NH}_3 = 14.01 + (3\times1.008) = 17.034\ \text{g/mol}$

Step2: Mass of $\text{NH}_3$: moles×molar mass

$\text{Mass} = 0.750\ \text{mol} \times 17.034\ \text{g/mol} \approx 12.8\ \text{g}$

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Step1: Calculate molar mass of $\text{CaCl}_2$

Molar mass of $\text{CaCl}_2 = 40.08 + (2\times35.45) = 110.98\ \text{g/mol}$

Step2: Mass of $\text{CaCl}_2$: moles×molar mass

$\text{Mass} = 1.25\ \text{mol} \times 110.98\ \text{g/mol} = 139\ \text{g}$

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

Molar mass of $\text{CO}_2 = 12.01 + (2\times16.00) = 44.01\ \text{g/mol}$

Step2: Mass of $\text{CO}_2$: moles×molar mass

$\text{Mass} = 2.00\ \text{mol} \times 44.01\ \text{g/mol} = 88.0\ \text{g}$

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Step1: Calculate molar mass of $\text{Na}_2\text{SO}_4$

Molar mass of $\text{Na}_2\text{SO}_4 = (2\times22.99) + 32.07 + (4\times16.00) = 142.05\ \text{g/mol}$

Step2: Mass of $\text{Na}_2\text{SO}_4$: moles×molar mass

$\text{Mass} = 0.500\ \text{mol} \times 142.05\ \text{g/mol} = 71.0\ \text{g}$

Answer:

1. $1.00\ \text{mol}$
2. $1.00\ \text{mol}$
3. $1.00\ \text{mol}$
4. $1.00\ \text{mol}$
5. $12.8\ \text{g}$
6. $139\ \text{g}$
7. $88.0\ \text{g}$
8. $71.0\ \text{g}$