29) Given the reaction magnesium and iron(III) chloride forming magnesium chlori

Question

29) Given the reaction magnesium and iron(III) chloride forming magnesium chloride and elemental iron, which of the following is correct is 41.0 g of magnesium and 175 g of iron III) chloride are combined? a) Iron(III) chloride is the limiting reactant and 1.67g of magnesium are left in excess. b) Iron(III) chloride is the limiting reactant and 14.8g of magnesium are left in excess. c) Magnesium is the limiting reactant and 10.3g of iron III) chloride are left in excess. d) Magnesium is the limiting reactant and 10.3g of iron(III) chloride are left in excess. 30) Which substances are in excess when 3.00 mol of Pb, 1.50 mol of Pb02, and 5.00 mol of H2SO4 are reacted in the following equation? Pb + PbOz + 2 H2SO4 2 PbSO4 + 2 H2O a) Pb and PbO2 b) Pb and H2SO4 c) PbO2 and H2SO4 d) PbSO4 and H2O

Explanation / Answer

29)

3Mg + 2FeCl3 ------> 3MgCl2 + 2Fe

number of moles of Mg = 41/24.3 = 1.6872
number of moles of FeCl3 = 175/162.2 = 1.0789
3 moles of Mg reacts with 2 moles of FeCl3
1.7083 moles reacts with 2/3*1.7083 = 1.1389 moles of FeCl3
so limiting reagent is FeCl3.
2 moles of FeCl3 reacts with 3 moles of Mg
1.0789 moles of FeCl3 reacts with 3/2*1.0789 = 1.6183 moles of Mg
excess of Mg = 1.6872 - 1.6183 = 0.0689 moles
excess mass of Mg = 0.0689 *24.3 = 1.6742 g

Answer : C

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