Question

6) If 0.12 mole of C3H8O reacts with 0.1 mole of CrO3 and 0.11 mole of H2SO4 in the folIowing manner: 3C3H8O + 2CrO3 + 3H2SO4 → Cr2(SO4)3 + 3C3H6O + 6H2O ? I have put it in the following section with the answer - which I do not understand! Please help

6) If 0.12 mole of C3H8O reacts with 0.1 mole of CrO3 and 0.11 mole of H2SO4 in the following manner:

3C3H8O + 2CrO3 + 3H2SO4 → Cr2(SO4)3 + 3C3H6O + 6H2O

Then which of the following is the limiting reagent?

A) H2O
B) SO4
C) C3H8O
D) H2SO4

Result: Your answer is incorrect.
Your choice: N/A Correct choice: D

Explanation: The stoichiometric relationship of the reactants is 2 CrO3: 3 C3H8O: 3 H2SO4. Seeing how the amounts of H2SO4 and of C3H8O should be equal, having less of one of these reactants would indicate the limiting reagent. In this case, C3H8O is in excess with 0.12 moles in comparison to 0.11 moles of H2SO4. H2SO4 is therefore the limiting reagent.

Answer 1

The ratio of moles of reactants is the key.

Explanation:

The number of moles of each reactant is about 0,1 moles. But the molar ratio of the reactants (examine the chemical equation) is 3:2:3. So there is not enough of the reactants that require 3 moles. Since there is are 0.12moles of C3H8O and only 0.11moles H2SO4, and the ratio needed is 3:3, the H2SO4 must be the limiting reagent. There is an excess of the other reactants needed.