Moles I. How many moles are in: a. 25g of NaCl 58.5 b. 125g of HSO c. 100.0g of KMnO d. 74g of KCl e. 35 g of CuSO II. How many grams are in: a. 2.5 moles of NaCl b. 0.50 moles of HSO c. 1.70 moles of KMnO d. 0.25 moles of KCl e. 3.2 moles of CuSO
The Correct Answer and Explanation is:
I. Finding the number of moles in the given compounds:
The formula to calculate the number of moles is:Moles=Mass (g)Molar Mass (g/mol)\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}Moles=Molar Mass (g/mol)Mass (g)
We will calculate the molar mass for each compound and then use this formula to find the number of moles.
a) 25 g of NaCl
Molar mass of NaCl = 58.5 g/molMoles of NaCl=25 g58.5 g/mol≈0.427 moles\text{Moles of NaCl} = \frac{25 \, \text{g}}{58.5 \, \text{g/mol}} \approx 0.427 \, \text{moles}Moles of NaCl=58.5g/mol25g≈0.427moles
b) 125 g of H₂SO₄
Molar mass of H₂SO₄ = 2(1.008) + 32.06 + 4(16.00) = 98.08 g/molMoles of H₂SO₄=125 g98.08 g/mol≈1.275 moles\text{Moles of H₂SO₄} = \frac{125 \, \text{g}}{98.08 \, \text{g/mol}} \approx 1.275 \, \text{moles}Moles of H₂SO₄=98.08g/mol125g≈1.275moles
c) 100.0 g of KMnO₄
Molar mass of KMnO₄ = 39.10 + 54.94 + 4(16.00) = 158.04 g/molMoles of KMnO₄=100.0 g158.04 g/mol≈0.633 moles\text{Moles of KMnO₄} = \frac{100.0 \, \text{g}}{158.04 \, \text{g/mol}} \approx 0.633 \, \text{moles}Moles of KMnO₄=158.04g/mol100.0g≈0.633moles
d) 74 g of KCl
Molar mass of KCl = 39.10 + 35.45 = 74.55 g/molMoles of KCl=74 g74.55 g/mol≈0.993 moles\text{Moles of KCl} = \frac{74 \, \text{g}}{74.55 \, \text{g/mol}} \approx 0.993 \, \text{moles}Moles of KCl=74.55g/mol74g≈0.993moles
e) 35 g of CuSO₄
Molar mass of CuSO₄ = 63.55 + 32.07 + 4(16.00) = 159.62 g/molMoles of CuSO₄=35 g159.62 g/mol≈0.219 moles\text{Moles of CuSO₄} = \frac{35 \, \text{g}}{159.62 \, \text{g/mol}} \approx 0.219 \, \text{moles}Moles of CuSO₄=159.62g/mol35g≈0.219moles
II. Finding the mass in grams for the given moles:
The formula to calculate mass is:Mass (g)=Moles×Molar Mass (g/mol)\text{Mass (g)} = \text{Moles} \times \text{Molar Mass (g/mol)}Mass (g)=Moles×Molar Mass (g/mol)
a) 2.5 moles of NaCl
Mass of NaCl=2.5 moles×58.5 g/mol=146.25 g\text{Mass of NaCl} = 2.5 \, \text{moles} \times 58.5 \, \text{g/mol} = 146.25 \, \text{g}Mass of NaCl=2.5moles×58.5g/mol=146.25g
b) 0.50 moles of H₂SO₄
Mass of H₂SO₄=0.50 moles×98.08 g/mol=49.04 g\text{Mass of H₂SO₄} = 0.50 \, \text{moles} \times 98.08 \, \text{g/mol} = 49.04 \, \text{g}Mass of H₂SO₄=0.50moles×98.08g/mol=49.04g
c) 1.70 moles of KMnO₄
Mass of KMnO₄=1.70 moles×158.04 g/mol=269.67 g\text{Mass of KMnO₄} = 1.70 \, \text{moles} \times 158.04 \, \text{g/mol} = 269.67 \, \text{g}Mass of KMnO₄=1.70moles×158.04g/mol=269.67g
d) 0.25 moles of KCl
Mass of KCl=0.25 moles×74.55 g/mol=18.64 g\text{Mass of KCl} = 0.25 \, \text{moles} \times 74.55 \, \text{g/mol} = 18.64 \, \text{g}Mass of KCl=0.25moles×74.55g/mol=18.64g
e) 3.2 moles of CuSO₄
Mass of CuSO₄=3.2 moles×159.62 g/mol=511.78 g\text{Mass of CuSO₄} = 3.2 \, \text{moles} \times 159.62 \, \text{g/mol} = 511.78 \, \text{g}Mass of CuSO₄=3.2moles×159.62g/mol=511.78g
Summary:
I. Moles:
- NaCl: 0.427 moles
- H₂SO₄: 1.275 moles
- KMnO₄: 0.633 moles
- KCl: 0.993 moles
- CuSO₄: 0.219 moles
II. Mass:
- NaCl: 146.25 g
- H₂SO₄: 49.04 g
- KMnO₄: 269.67 g
- KCl: 18.64 g
- CuSO₄: 511.78 g
By using the molar masses and the moles formula, you can easily calculate moles from mass and mass from moles. Always ensure that you use the correct molar mass for each compound!
