strong acid-base titrations chapter 17. neutralization reactions review generally, when solutions of...
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Strong Acid-Base Titrations
Chapter 17
Neutralization Reactions ReviewGenerally, when solutions of an acid and a base are combined, the products are a salt and water.
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
Neutralization ReactionsWhen a strong acid reacts with a strong base, the net ionic
equation is…
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) Na+ (aq) + Cl- (aq) + H2O (l)
Net Ionic Equation: H+ (aq) + OH- (aq) H2O (l)
The K for this reaction is 1014
Neutralization reactions
• When a strong base is added to a solution of weak acid, the following neutralization reaction occurs:
Conj. Acid + OH- conj. Base + H2O
• When a strong acid is added to a solution of a weak base, a neutralization reaction occurs:
Conj base + H3O+ conj acid + H2O
Titration
A known concentration of base (or acid) is slowly added to a solution of acid (or base).
Titration
A pH meter or indicators are used to determine when the solution has reached the equivalence point, at which the stoichiometric amount of acid equals that of base.
• The initial pH (initial acid) is determined by the initial concentration of the strong acid.
• Major substances present: H+ and Cl-
Titration of a Strong Acid with a Strong Base
• From the start of the titration to near the equivalence point, the pH goes up slowly.
• As strong base is added, the pH increases slowly because the base is neutralized by the acid.
• Major substances present: H+ , Cl-, Na+
Titration of a Strong Acid with a Strong Base
Titration of a Strong Acid with a Strong Base
• The pH of the solution before the equivalence point increases quickly because it is determined by the concentration of the aced that has not yet been neutralized.
Titration of a Strong Acid with a Strong Base
• At the equivalence point, moles acid = moles base based on stoichiometry of reaction, and the solution contains only water and the salt from the cation of the base and the anion of the acid.
• The pH at equivalence point for a strong acid and strong base is always 7 exactly.
Titration of a Strong Acid with a Strong Base
• The pH after the equivalence point is determined by the concentration of the excess NaOH.
• As more base is added, the increase in pH again levels off
Practice ProblemCalculate the pH when 49.0 mL of 0.100 M
NaOH solution have been added to 50.0 mL of 0.100 M HCl solution.
Step 1: figure out how many moles of H+ are present in solution
0.0500 L soln x 0.100 mol H+/1 L soln = 5.00 x 10-3 mol H+
Step 2: figure out how many moles of OH- are added
0.0490 L soln x 0.100 mol OH- /1 L soln = 4.90 x 10-3 mol OH-
Calculate the pH when 49.0 mL of 0.100 M NaOH solution have been added to 50.0 mL of 0.100 M HCl solution.
Step 3: Because the equivalence point has not been reached, there are more moles of H+ present. ICE Table
H+ OH- H2O(l)
Initial 5.00 x 10-3
mol0 -
Change 4.90 x 10-3 mol
-
Equilibrium 0.10 x 10-3 mol
0 -
H+ OH- H2O(l)
Initial (before addition)
5.00 x 10-3
mol0 -
Change (addition)
4.90 x 10-3 mol
-
Equilibrium (after addition)
0.10 x 10-3 mol
0 -
Step 4: Determine the total volume of the mixed solution
0.050 L + 0.049 L = 0.0990 L
Step 5: Determine concentration of H+ and then pH
[H+] = 0.10 x 10-3 mol/0.0990 L = 1.0 x 10-3 M
pH = -log(1.0x10-3)