The number of moles of excess reactant is used in the experiment is 0.33 moles. The number of moles of aluminium sulphates was obtained 0.129 moles if the percentage yield is 77%.
2Al(OH)3(aq) + 3H2SO4(aq) -----> Al2(SO4)3(aq) + 6H2O(l)
Number of moles of Al(OH)3 = 0.500 mol
Number of moles of H2SO4 = 0.500 mol
We have to determine the limiting reactant as follows;
2 moles of Al(OH)3 reacts with 3 moles of H2SO4
0.500 moles of Al(OH)3 reacts with 0.500 moles × 3 moles/2 moles
= 0.75 moles of H2SO4.
This means that H2SO4 is limiting reactant
Since 3 moles of H2SO4 reacts with 2 moles of Al(OH)3
0.500 moles of H2SO4 reacts with 0.500 × 2 moles /3 moles
= 0.33 moles
Only 0.33 moles of excess reactant was used in the experiment.
3 moles of H2SO4 yields 1 mole of Al2(SO4)3
0.500 moles of H2SO4 yields 0.500 moles × 1 mole/3 moles = 0.167 moles
Theoretical yield of Al2(SO4)3 = 0.167 moles
% yield = actual yield/Theoretical yield × 100/1
Actual yield = % yield × Theoretical yield /100
Actual yield = 77 × 0.167/100
Actual yield = 0.129 moles
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