Titration

Strong acids ionize almost completely Weak acids don’t ionize very much not[H 3 O +1 ] not same as acid concentration

[H 3 O +1 ] Can’t be measured directly Determined by comparison

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

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

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

Titration End-pointEnd-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 Volume of M NaOH added (ml) pH Equivalence Pt Phenolphthalein Color change: 8.2 to 10  0 ml  40ml   20 ml

M H+1 V H+1 = M OH-1 V OH-1 M H+1 = molarity of H +1 M OH-1 = molarity of OH -1 V H+1 = volume of H +1 V OH-1 = volume of OH -1

M a V a = M b V b 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 then need to modify the equation: (#H’s)(M a )(V a ) = (M b )(V b )(#OH’s)

Titration Problem # mL 35.0mL0.100M NaOHIn 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 HNO 3 + NaOH  H 2 O + NaNO 3 HNO 3 is a monoprotic acid NaOH is a monohydroxy base

Variables M a = ? V a = 40.0 mL M b = M V b = 35.0 mL

Plug and Chug X (40.0 mL) = (0.100 M )(35.0 mL) X = M HNO 3

Titration Problem #2 What is the concentration of a hydrochloric acid solution50.0 mL 0.250M KOH 20.0mL of the HCl solutionWhat 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  H 2 O + KCl HNO 3 is a monoprotic acid KOH is a monohydroxy base

Variables M a = X V a = 20.0 mL M b = M V b = 50.0 mL

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

Titration Problem #3 What is the concentration of a sulfuric acid solution50.0mL of a 0.25 M KOH 20.0mL of the H 2 SO 4 solutionWhat 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 H 2 SO 4 solution of unknown concentration?

Neutralization Reaction H 2 SO KOH  2 H 2 O + K 2 SO 4 H 2 SO 4 is a diprotic acid KOH is a monohydroxy base

Variables M a = X V a = 20.0mL M b = 0.25M V b = 50.0mL

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