Acids & Bases Lesson 13 Weak Base/Strong Acid calculations

Strong acid and strong base Weak acid and STRONG BASE Weak base and STRONG ACID Three types of Titrations

Choosing an Indicator When you choose an indicator, you must pick one so that the transition point of the indicator matches the equivalence point of the titration. Look at the salts produced, if Rule of thumb Salt Equivalence Point SA + SBNeutral 7 WA + SBBasic 9 WB + SAAcidic 5

3. Titration Curve: Strong Acid and Weak Base HCl + NH 3 → NH 4 + +Cl - acid salt IndicatorpH = 5Methyl Red- see ind chart 60 mL of 1.0 M NH 3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH 3 added M HCl pH = 0 Acid Salt pH  M NH 3 pH  10

Weak base and STRONG ACID We expect to produce An acidic solution. Therefore, equivalence point at pH <7 Indicators around pH = 5 Rules found through experiments to make your life EASY.

Weak base and STRONG ACID Rules: pKb = pOH ½  means pH when half Volume is used, NOT HALF pH!!!! Kb = 10 –pKb or Kb = 10 -pOH ½ Kb = [ OH - ] 1/2 where [OH] 1/2 can be found from pOH 1/2 [Base] equilibrium = [ OH - ] 2 ….. this [OH] is found from pH or pOH initial Kb Kb found from above equation [Base]original= [Base]eq + [OH] from pH initial

Weak base and STRONG ACID The following data was obtained when titrating ethylamine, a monoprotic weak base, with HCl mL= volume of ethylamine solution titrated mL = volume of HCl required to get to equivalence point = initial pH of ethylamine solution = pH at 9.60 mL point of titration A) Calculate the Kb value for ethylamine

Weak base and STRONG ACID The following data was obtained when titrating ethylamine, a monoprotic weak base, with HCl mL= volume of ethylamine solution titrated mL = volume of HCl required to get to equivalence point = initial pH of ethylamine solution = pH at 9.60 mL point of titration B) Calculate the initial [ethylamine]

Weak base and STRONG ACID The following data was obtained when titrating ethylamine, a monoprotic weak base, with HCl mL= volume of ethylamine solution titrated mL = volume of HCl required to get to equivalence point = initial pH of ethylamine solution = pH at 9.60 mL point of titration C) Calculate the [HCl] used

Weak base and STRONG ACID The following data was obtained when titrating ethylamine, a monoprotic weak base, with HCl mL= volume of ethylamine solution titrated mL = volume of HCl required to get to equivalence point = initial pH of ethylamine solution = pH at 9.60 mL point of titration D) Suggest a suitable indicator.

Homework #127 on page 176