Name __________________________________
HONORS Task Card
Finding the Limiting Reagent
Solving Limiting Reactant Problems:
Step 1 – Balance the chemical equation if necessary
Step 2 – Determine the molar mass of each reactant
Step 3 – Determine the number of moles of each reactant that you have
Step 4 – Multiply the number of moles of each reactant by their coefficients to identify the limiting
reactant
Step5 – Use the limiting reactant to determine the maximum amount of product you can make
Example:
Imagine you start with 10g of Mg(OH)2 and 15g of HCl. How much MgCl2 will be produced?
Step 1: Determine the balanced reaction
Mg(OH)2(s) + 2HCl(aq)  MgCl2(aq) + 2H2O(l)
Step 2: Determine the molar mass of each compound
Mg(OH)2 = 58.3 g/mol
HCl = 36.5 g/mol
Step 3: Determine the number of moles of each reactant that you have
Moles of Mg(OH)2 = 10g ÷ 58.3g/mol = 0.17 mol
Moles of HCl = 15g ÷ 36.5g/mol = 0.4 mol
Step 4: Multiply the number of moles of each reactant by their coefficients to identify the limiting reactant
0.17mol Mg(OH)2 x 1 = 0.17 mol Mg(OH)2  LIMITING REACTANT
0.4mol HCl x 2 = 0.8 mol HCl
Step 5: Use the limiting reactant to determine the maximum amount of product you can make
0.17mol Mg(OH)2 x (1mol MgCL2/1mol Mg(OH)2) = 0.17mol MgCl2
Molar Mass of MgCl2 = 95.3 g/mol
0.17mol MgCl2 x 95.3g/mol = 16.2g MgCl2 will be produced
Directions: Complete the following questions on your own!
1. 15.00 g Al2S3and 10.00 g H2O react until the limiting reagent is used up. Here is the balanced equation for
the reaction: Al2S3 + 6 H2O  2Al(OH)3 + 3 H2S
(A) Which is the limiting reactant, Al2S3 or H2O?
(B) What is the maximum mass of H2S which can be formed from the limiting reactant determined in
part A?
Name __________________________________
2. Use the following reaction to answer the question below.
16Na + S8  8Na2S
Which reactant is the limiting reactant, 2 grams of Na, or 12 grams of S8?
3. For the reaction: Na2O + H2O NaOH
A) You react 12.4 g of Na2O and 42.1 g of H2O, which reactant is the limiting reactant?
B) What mass of NaOH could be made from the mass of the limiting reactant you determined in part A?
4. For the reaction: C + H2 CH4
A) Which is the limiting reactant, 10.0 g of H2 of 5.0 g of C?
B) How many moles of CH4 can be made from the limiting reactant determined in part A?