14 - Limiting Reagent SCH4C Chemical Calculations

14 - Limiting Reagent SCH4C – Chemical Calculations

Date: ______

Limiting Reagent

  • In a chemical reaction, the ______amount of compound which can be formed will be limited by the amount of reactants present
  • Often one of the reactants will run out before the other
  • The reactant which runs out is known as the ______
  • The reagent left in excess is called the ______
  • Example: Consider the construction of a car.
  • If we have 10 car bodies, 22 wiper blades and 32 tires, how many cars can we make?
  • How much is left over?

  • Example: If 5.76 g of NaCl is reacted with 9.52 g of AgNO3, calculate the maximum amount of AgCl which could be produced.

Example: How much excess reagent is left over?

  • Ca(NO3)2 reacts with Na3PO4 to produce a solid, Ca3(PO4)2. Calculate the amount of Ca3(PO4)2 if 18.8 g of Ca(NO3)2 and 15.2 g of Na3PO4 are reacted. Calculate the amount of excess after.


Practice Questions

1.  Given the following unbalanced reaction:

C3H8(g) + O2(g) → CO2(g) + H2O(g)

a)  If you start with 14.8 g of C3H8(g) and 3.44 g of O2(g), determine the limiting reagent

b)  Determine the number of moles of carbon dioxide produced

c)  Determine the number of grams of H2O(g) produced

d)  Determine the number of grams of excess reagent left

2.  Given the following unbalanced reaction:

Al2(SO3)3(aq) + NaOH(aq) → Na2SO3(aq) + 2 Al(OH)3(s)

a)  If 10.0 g of Al2(SO3)3(aq) is reacted with 10.0 g of NaOH(aq), determine the limiting reagent

b)  Determine the number of moles of Al(OH)3(s) produced

c)  Determine the number of grams of Na2SO3(aq) produced

d)  Determine the number of grams of excess reagent left over in the reaction

3.  Given the following unbalanced reaction:

Al2O3(aq) + Fe(s) → Fe3O4(aq) + Al(s)

a)  If 25.4 g of Al2O3(aq) is reacted with 10.2 g of Fe(s), determine the limiting reagent

b)  Determine the number of moles of Al(s) produced

c)  Determine the number of grams of Fe3O4(aq) produced

d)  Determine the number of grams of excess reagent left over in the reaction

4.  Consider the following unbalanced reaction:

I2O5(g) + CO(g) → CO2(g) + I2(s)

If 80.0 grams of iodine(V) oxide, I2O5(g), reacts with 28.0 grams of carbon monoxide, CO(g). Determine the mass of iodine I2(s), which could be produced?

5.  Consider the reaction between magnesium and oxygen.

a)  Which element is in excess when 3.00 grams of magnesium is ignited in 2.20 grams of pure oxygen?

b)  What element is in excess?

c)  What mass of magnesium oxide is formed?

6.  Silver nitrate reacts with iron(III) chloride to give silver chloride and iron(III) nitrate. In a particular experiment, it was planned to mix a solution containing 25.0 g of silver nitrate with another solution containing 45.0 grams of iron(III) chloride.

a)  Write the balanced chemical equation for the above reaction.

b)  Which reactant is the limiting reactant?

c)  What is the maximum number of moles of silver chloride that could be obtained from this mixture?

d)  What is the maximum number of grams of silver chloride that could be obtained?

e)  How many grams of the reactant in excess will remain after the reaction is over?


Answers:

1.  Balanced reaction:

C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

a)  O2(g)

b)  0.065 mol CO2(g)

c)  1.56 g H2O(g)

d)  13.86 g C3H8(g)

2. Balanced reaction:

Al2(SO3)3(aq) + 6 NaOH(aq) → 3 Na2SO3(aq) + 2 Al(OH)3(s)

a)  Al2(SO3)3

b)  0.068 mol Al(OH)3

c)  12.85 g Na2SO3

d)  1.84 g NaOH

3. Balanced reaction:

4 Al2O3 + 9 Fe → 3 Fe3O4 + 8 Al

a)  Fe

b)  0.16 mol Al

c)  14.12 g Fe3O4

d)  17.13 g Al2O3

4. Balanced reaction:

I2O5(g) + 5 CO(g) → 5 CO2(g) + I2(s)

50.7 g I2(s)

5. Balanced reaction:

2 Mg(s) + O2(g) → 2 MgO(s)

a)  O2(g)

b)  0.226 g O2(g)

c)  4.97 g MgO(s)

6. Balanced reaction:

a)  3 AgNO3(aq) + FeCl3(aq) → 3 AgCl(s) + Fe(NO3)3(aq)

b)  AgNO3(aq)

c)  0.147 mol AgCl(s)

d)  21.1 g AgCl(s)

e)  37.1 g FeCl3(aq)

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