Titration

Titration Strong acids ionize almost completely Weak acids don’t ionize very much [H3O+1] not same as acid concentration

[H3O+1] Can’t be measured directly Determined by comparison

Acid-Base Titration Carefully controlled neutralization reaction Requires standard solution & acid-base indicator Standard solution is: acid/base of known concentration

Titration Standard solution slowly added to unknown solution As solutions mix: neutralization reaction occurs Eventually: enough standard solution is added to neutralize the unknown solution  Equivalence point

Equivalence point Total # moles H+1 ions donated by acid = total # moles H+1 accepted by base Total moles H+1 = total moles OH-1

Titration End-point = point at which indicator changes color if indicator chosen correctly: end-point very close to equivalence point

Titration of a strong acid with a strong base 14- Phenolphthalein Color change: 8.2 to 10  pH 7- Equivalence Pt  0-    Volume of 0.100 M NaOH added (ml) 0 ml 40ml 20 ml

MH+1VH+1 = MOH-1VOH-1 MH+1 = molarity of H+1 MOH-1 = molarity of OH-1 VH+1 = volume of H+1 VOH-1 = volume of OH-1

MaVa = MbVb True for: monoprotic acids and monohydroxy bases diprotic acids and dihydroxy bases triprotic acids and trihydroxy bases

If: # H’s in acid ≠ # OH’s in base need to modify equation: (#H’s)(Ma)(Va) = (Mb)(Vb)(#OH’s)

Titration Problem #1 In a titration of 40.0 mL of a nitric acid solution, the end point is reached when 35.0mL of 0.100M NaOH is added Calculate the concentration of the nitric acid solution

Neutralization Reaction HNO3 + NaOH  H2O + NaNO3 HNO3 is a monoprotic acid NaOH is a monohydroxy base

Variables Ma = ? Va = 40.0 mL Mb = 0.100 M Vb = 35.0 mL

Plug and Chug X (40.0 mL) = (0.100 M )(35.0 mL) X = 0.875 M HNO3

Titration Problem #2 What is the concentration of a hydrochloric acid solution if 50.0 mL of a 0.250M KOH solution are needed to neutralize 20.0mL of the HCl solution of unknown concentration?

Neutralization Reaction KOH + HCl  H2O + KCl HNO3 is a monoprotic acid KOH is a monohydroxy base

Variables Ma = X Va = 20.0 mL Mb = 0.250 M Vb = 50.0 mL

Plug and Chug X (20.0 mL) = (0.250 M) (50.0 mL) X = 0.625 M HCl

Titration Problem #3 What is the concentration of a sulfuric acid solution if 50.0mL of a 0.25 M KOH solution are needed to neutralize 20.0mL of the H2SO4 solution of unknown concentration?

Neutralization Reaction H2SO4 + 2 KOH  2 H2O + K2SO4 H2SO4 is a diprotic acid KOH is a monohydroxy base

Variables Ma = X Va = 20.0mL Mb = 0.25M Vb = 50.0mL

Plug and Chug (2)(X)(20.0ml) = (0.25M)(50.0ml)(1) X = 0.3125 M (sulfuric acid)