When 0.500 moles of boron trichloride react with 1.20 moles hydrogen gas to produce elemental boron and hydrogen chloride gas, the actual yield of boron was 66.4 % of the theoretical yield. The mass of boron obtained was _____ g.
Please help I'm stuck on it.
2BCl3 + 3H2 ==> 2B + 6HCl
0.5 mol BCl2 will produce 0.5 mol B if you have all of the H2 needed.
1.20 mols H2 gas will produce 1.20 x (2 mol B/3 mols H2) = 1.20 x 2/3 = 0.8 mol B if you hadd all of the BCl3 needed.
Both answers can't be right; the correct answer in limiting reagent problems is ALWAYS the smaller value and the reagent producing that value is the limiting reagent. In this case the LR is BCl3 and H2 is the excess reagent so you can produce 0.5 mol B as the theoretical yield. 0.5 mols x atomic mass B = estimated 5 g B. The yield is only 66.4%; therefore, you can collect only estimated 5 x 0.664 = ? g B.
Can we use moles of HCl instead of B to calculate limiting reactant?
Yes. The limiting reagent will always produce the LEAST product (whichever one you choose)
3.59
To find the mass of boron obtained, we need to follow these steps:
Step 1: Write the balanced chemical equation for the reaction:
BCl3 + 3H2 → B + 3HCl
Step 2: Calculate the number of moles of boron trichloride (BCl3) and hydrogen gas (H2) actually used in the reaction:
0.500 moles BCl3
1.20 moles H2
Step 3: Identify the limiting reactant by comparing the mole ratios in the balanced equation:
From the balanced equation, it can be seen that for every 1 mole of BCl3, 3 moles of H2 are required. Therefore, the limiting reactant is BCl3 because we have less of it compared to H2.
Step 4: Determine the theoretical yield of boron (B) using the limiting reactant:
Since the limiting reactant is BCl3, we use its moles to calculate the moles of B produced:
0.500 moles BCl3 * (1 mole B / 1 mole BCl3) = 0.500 moles B
Step 5: Calculate the theoretical yield of boron using the molar mass of boron (molar mass of B = 10.81 g/mol):
0.500 moles B * 10.81 g/mol = 5.405 g B (theoretical yield)
Step 6: Calculate the actual yield based on the given information:
The actual yield of boron was 66.4% of the theoretical yield. Therefore, the actual yield of boron can be calculated as:
Actual yield = 66.4% * (5.405 g)
Step 7: Calculate the mass of boron obtained:
Mass of boron obtained = Actual yield (g)
By following these steps, you will be able to find the mass of boron obtained.