10/25/2011
Acid/Base and Limiting Reagent
75.0 mL of 0.250 M HCl is added to 225.0 mL of 0.0550 M Ba(OH)2
solution. What is the concentration of the excess H+ or OH- ions
left in this solution?
2 HCl(aq) + Ba(OH)2(aq)
75.0 mL
0.250 M
 2 H2O(l) + BaCl2(aq)
225.0 mL
0.0550 M
1. How many moles of each reactant?
2. Which is limiting?
3. How much H+ or OH- is left over?
4. What is the new volume?
5. What is the concentration of the excess reactant?
Acid/Base and Limiting Reagent
2 HCl(aq) + Ba(OH)2(aq)
0.0750 L
* 0.250 M
 2 H2O(l) + BaCl2(aq)
0.225 L
* 0.0550 M
0.018750 moles 0.012375 moles
1. How many moles of each reactant? Let’s focus on net ionic eqn.
0.01875 moles H+
2(0.012375 moles) = 0.02475 moles OH2. Which is limiting?
2:1 ratio…0.01875 moles H+ require 0.009375 moles OH- (H+ is LR)
3. How much H+ or OH- is left over?
0.02475 moles OH- less 0.009375 moles used, so 0.015375 moles OH- left
4. What is the new volume?
0.0750 L plus 0.225 L = 0.300 L
5. What is the concentration of the excess reactant?
0.015375 moles OH- / 0.300 L = 0.05125 = 0.0513 M OHThe concentration for Ba(OH)2would be 0.0256 M.
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