Determining the Limiting Reagents
Worksheet
Limiting Reagents with Masses
1. 12g of sodium are reacted with 20g of water. Which reagent is limiting?
2Na + 2H2O
→
2NaOH + H2
Working Out
Moles Na = 12 / 23.0 = 0.522 mol
Moles H2O = 20 / 18.0 = 1.11 mol
Ratio Na : H2O is 2:2 (or 1:1).
0.522 mol of Na needs 0.522 mol of H2O.
We have 1.11 mol (Excess).
Limiting Reagent: Sodium
Moles H2O = 20 / 18.0 = 1.11 mol
Ratio Na : H2O is 2:2 (or 1:1).
0.522 mol of Na needs 0.522 mol of H2O.
We have 1.11 mol (Excess).
Limiting Reagent: Sodium
2. 60kg of methane are reacted with 42kg of steam. Which reagent is limiting?
CH4 + H2O
→
CO + 3H2
Working Out
Moles CH4 = 60,000 / 16.0 = 3750 mol
Moles H2O = 42,000 / 18.0 = 2333 mol
Ratio 1 : 1.
3750 mol CH4 needs 3750 mol H2O.
We only have 2333 mol.
Limiting Reagent: Steam (Water)
Moles H2O = 42,000 / 18.0 = 2333 mol
Ratio 1 : 1.
3750 mol CH4 needs 3750 mol H2O.
We only have 2333 mol.
Limiting Reagent: Steam (Water)
3. One tonne of sulfur is reacted with 1.2 tonnes of oxygen, producing sulfur dioxide. Which reagent is limiting?
S + O2
→
SO2
Working Out
Moles S = 1,000,000 / 32.1 = 31,153 mol
Moles O2 = 1,200,000 / 32.0 = 37,500 mol
Ratio 1 : 1.
31,153 mol S needs 31,153 mol O2.
We have 37,500 mol (Excess).
Limiting Reagent: Sulfur
Moles O2 = 1,200,000 / 32.0 = 37,500 mol
Ratio 1 : 1.
31,153 mol S needs 31,153 mol O2.
We have 37,500 mol (Excess).
Limiting Reagent: Sulfur
4. One tonne of sulfur dioxide is reacted with 1.2 tonnes of oxygen, producing sulfur trioxide. Which reagent is limiting?
2SO2 + O2
→
2SO3
Working Out
Moles SO2 = 1,000,000 / 64.1 = 15,600 mol
Moles O2 = 1,200,000 / 32.0 = 37,500 mol
Ratio 2 : 1.
15,600 mol SO2 needs 7,800 mol O2.
We have 37,500 mol (Excess).
Limiting Reagent: Sulfur Dioxide
Moles O2 = 1,200,000 / 32.0 = 37,500 mol
Ratio 2 : 1.
15,600 mol SO2 needs 7,800 mol O2.
We have 37,500 mol (Excess).
Limiting Reagent: Sulfur Dioxide
5. 46 kg of nitrogen are reacted against 20kg of hydrogen. Which reagent is limiting?
N2 + 3H2
→
2NH3
Working Out
Moles N2 = 46,000 / 28.0 = 1643 mol
Moles H2 = 20,000 / 2.0 = 10,000 mol
Ratio 1 : 3.
1643 mol N2 needs (1643 × 3) = 4929 mol H2.
We have 10,000 mol (Excess).
Limiting Reagent: Nitrogen
Moles H2 = 20,000 / 2.0 = 10,000 mol
Ratio 1 : 3.
1643 mol N2 needs (1643 × 3) = 4929 mol H2.
We have 10,000 mol (Excess).
Limiting Reagent: Nitrogen
6. 100g of fluorine are reacted against 90g of calcium. Which reagent is limiting?
Ca + F2
→
CaF2
Working Out
Moles F2 = 100 / 38.0 = 2.63 mol
Moles Ca = 90 / 40.1 = 2.24 mol
Ratio 1 : 1.
We have less Calcium moles than Fluorine moles.
Limiting Reagent: Calcium
Moles Ca = 90 / 40.1 = 2.24 mol
Ratio 1 : 1.
We have less Calcium moles than Fluorine moles.
Limiting Reagent: Calcium
7. 18g of copper oxide are reacted against 24g of carbon. Which reagent is limiting?
2CuO + C
→
2Cu + CO2
Working Out
Moles CuO = 18 / 79.5 = 0.226 mol
Moles C = 24 / 12.0 = 2.00 mol
Ratio 2 : 1.
0.226 mol CuO needs 0.113 mol C.
We have 2.00 mol (Huge Excess).
Limiting Reagent: Copper Oxide
Moles C = 24 / 12.0 = 2.00 mol
Ratio 2 : 1.
0.226 mol CuO needs 0.113 mol C.
We have 2.00 mol (Huge Excess).
Limiting Reagent: Copper Oxide
8. 40g of propane are reacted with 35g of oxygen. Which reagent is limiting?
C3H8 + 5O2
→
3CO2 + 4H2O
Working Out
Moles Propane = 40 / 44.1 = 0.907 mol
Moles Oxygen = 35 / 32.0 = 1.09 mol
Ratio 1 : 5.
0.907 mol Propane needs (0.907 × 5) = 4.54 mol Oxygen.
We only have 1.09 mol.
Limiting Reagent: Oxygen
Moles Oxygen = 35 / 32.0 = 1.09 mol
Ratio 1 : 5.
0.907 mol Propane needs (0.907 × 5) = 4.54 mol Oxygen.
We only have 1.09 mol.
Limiting Reagent: Oxygen
Limiting Reagents with Ranges of States
1. A 5g piece of sodium reacts with 12cm3 of 0.1moldm-3 of HCl. Which reagent is limiting?
2Na + 2HCl
→
2NaCl + H2
Working Out
Moles Na = 5 / 23.0 = 0.217 mol
Moles HCl = (12/1000) × 0.1 = 0.0012 mol
Ratio 1 : 1.
We have much less HCl than Na.
Limiting Reagent: HCl
Moles HCl = (12/1000) × 0.1 = 0.0012 mol
Ratio 1 : 1.
We have much less HCl than Na.
Limiting Reagent: HCl
2. 32 kg of methane reacted with 20m3 of oxygen. Which reagent is limiting?
CH4 + 2O2
→
CO2 + 2H2O
Working Out
Moles CH4 = 32,000 / 16.0 = 2000 mol
Moles O2 = 20,000 dm3 / 24.0 = 833 mol
Ratio 1 : 2.
2000 mol CH4 needs 4000 mol O2.
We only have 833 mol.
Limiting Reagent: Oxygen
Moles O2 = 20,000 dm3 / 24.0 = 833 mol
Ratio 1 : 2.
2000 mol CH4 needs 4000 mol O2.
We only have 833 mol.
Limiting Reagent: Oxygen
3. 40g of phosphorous trichloride reacts with 25 cm3 of 1moldm-3 potassium iodide. Which reagent is limiting?
(Assuming 1:3 reaction: PCl3 + 3KI → PI3 + 3KCl)
Working Out
Moles PCl3 = 40 / 137.5 = 0.291 mol
Moles KI = (25/1000) × 1 = 0.025 mol
Ratio 1 : 3.
0.291 mol PCl3 needs (0.291 × 3) = 0.873 mol KI.
We only have 0.025 mol.
Limiting Reagent: Potassium Iodide
Moles KI = (25/1000) × 1 = 0.025 mol
Ratio 1 : 3.
0.291 mol PCl3 needs (0.291 × 3) = 0.873 mol KI.
We only have 0.025 mol.
Limiting Reagent: Potassium Iodide
4. 50g of iodine were reacted with 50dm3 of fluorine gas, forming iodine pentafluoride. Which reagent is limiting?
I2 + 5F2
→
2IF5
Working Out
Moles I2 = 50 / 253.8 = 0.197 mol
Moles F2 = 50 / 24.0 = 2.08 mol
Ratio 1 : 5.
0.197 mol I2 needs (0.197 × 5) = 0.985 mol F2.
We have 2.08 mol (Excess).
Limiting Reagent: Iodine
Moles F2 = 50 / 24.0 = 2.08 mol
Ratio 1 : 5.
0.197 mol I2 needs (0.197 × 5) = 0.985 mol F2.
We have 2.08 mol (Excess).
Limiting Reagent: Iodine
5. 50m3 of nitrogen was reacted with 80m3 of hydrogen. Which reagent is limiting?
N2 + 3H2
→
2NH3
Working Out
Volume Ratio is the same as Mole Ratio for gases.
Ratio 1 : 3.
50 m3 N2 needs 150 m3 H2.
We only have 80 m3.
Limiting Reagent: Hydrogen
Ratio 1 : 3.
50 m3 N2 needs 150 m3 H2.
We only have 80 m3.
Limiting Reagent: Hydrogen
6. Acidified KMnO4 was reacted with KCl. Which is limiting?
- 5cm3 of 0.2M KMnO4
- 8cm3 of 0.5M H2SO4
- 10cm3 of 0.2M KCl
16H+ + 2MnO4– + 10Cl–
→
…
Working Out
Calculate Moles:
MnO4–: 0.005 × 0.2 = 0.001 mol
H+ (from H2SO4): 0.008 × 0.5 × 2 = 0.008 mol
Cl–: 0.010 × 0.2 = 0.002 mol
Normalize by Coefficient:
MnO4–: 0.001 / 2 = 0.0005
H+: 0.008 / 16 = 0.0005
Cl–: 0.002 / 10 = 0.0002
The smallest value indicates the limiting reagent.
Limiting Reagent: Chloride Ions (Cl–)
MnO4–: 0.005 × 0.2 = 0.001 mol
H+ (from H2SO4): 0.008 × 0.5 × 2 = 0.008 mol
Cl–: 0.010 × 0.2 = 0.002 mol
Normalize by Coefficient:
MnO4–: 0.001 / 2 = 0.0005
H+: 0.008 / 16 = 0.0005
Cl–: 0.002 / 10 = 0.0002
The smallest value indicates the limiting reagent.
Limiting Reagent: Chloride Ions (Cl–)