A chemist reacts 8.85 g of iron with an excess of hydrogen chloride to form hydrogen gas and iron choloride. How do you calcualte the theoretical yield and the percentage yield of hydrogen if .27g H2 are collected.
This is just a twist to the usual stoichiometry problem.
1. Write and balance the equation.
2. Convert g you have (in this case 8.85 g Fe) to moles. moles = grams/atomic mass.
3. Using the coefficients in the balanced equation, convert moles Fe to moles H2.
4. Now convert moles H2 to grams H2. grams = moles x molar mass. This value you have obtained is the THEORETICAL YIELD and the process is a straight stoichiometry problem.
5. Now that you have the theoretical yield, you can calculate the percent yield.
%yield = (actual yield/theoretical yield)*100 = ??
0.27 g H2 is the actual yield.
To calculate the theoretical yield of hydrogen gas, we need to determine the balanced chemical equation for the reaction between iron and hydrogen chloride. The balanced equation is:
2Fe + 6HCl → 2FeCl3 + 3H2
From the balanced equation, we can see that 2 moles of iron react with 6 moles of hydrogen chloride to produce 3 moles of hydrogen gas.
Step 1: Calculate the number of moles of iron used.
- Given mass of iron = 8.85 g
- Calculate the molar mass of iron (Fe):
Molar mass of Fe = 55.85 g/mol
- Calculate moles of iron:
Moles of Fe = Mass of Fe ÷ Molar mass of Fe
Step 2: Calculate the theoretical yield of hydrogen gas.
- Since 2 moles of iron produce 3 moles of hydrogen, we can use the mole ratio to calculate the moles of hydrogen produced:
Moles of H2 = Moles of Fe × (3 moles H2 / 2 moles Fe)
- Convert moles of hydrogen gas to grams using its molar mass:
Molar mass of H2 = 2.016 g/mol
Mass of H2 = Moles of H2 × Molar mass of H2
Step 3: Calculate the percentage yield of hydrogen gas.
- Percentage yield = (Actual yield ÷ Theoretical yield) × 100
- Actual yield = 0.27 g (given)
- Theoretical yield = Mass of H2 (calculated in Step 2)
Now, let's calculate the theoretical yield and the percentage yield of hydrogen gas.
Step 1:
Moles of Fe = 8.85 g ÷ 55.85 g/mol
Moles of Fe = 0.1582 mol
Step 2:
Moles of H2 = 0.1582 mol × (3 mol H2 / 2 mol Fe)
Moles of H2 = 0.2373 mol
Mass of H2 = 0.2373 mol × 2.016 g/mol
Mass of H2 = 0.4787 g
Theoretical yield of hydrogen gas = 0.4787 g
Step 3:
Percentage yield = (0.27 g ÷ 0.4787 g) × 100
Percentage yield = 56.34%
Therefore, the theoretical yield of hydrogen gas is 0.4787 g, and the percentage yield is 56.34%.