Titration

TitrationTitration

Acid–Base TitrationAcid–Base TitrationThe concentration of an acid The concentration of an acid especially a weak one or a weak especially a weak one or a weak base in water is difficult to base in water is difficult to measure directly.measure directly.But we can calculate the conc But we can calculate the conc from the results of titration.from the results of titration.

A titration is a carefully controlled A titration is a carefully controlled neutralization reaction.neutralization reaction.Titration is a lab technique for Titration is a lab technique for measuring the conc of an measuring the conc of an unknown acid or baseunknown acid or base

Acid–Base TitrationAcid–Base TitrationThe average titration involves The average titration involves three componentsthree components

An acid or base of unknown An acid or base of unknown concentrationconcentrationYou need a You need a standard solnstandard soln

A standard is A standard is a solution of a solution of known conc known concShould be Should be opposite of opposite of the unknownthe unknown

An indicatorAn indicator

Acid–Base TitrationAcid–Base TitrationThe purpose of the indicator is The purpose of the indicator is used to indicate when the acid used to indicate when the acid and base ions are equaland base ions are equal

Let’s the person performing the Let’s the person performing the titration know when neutralization titration know when neutralization has occurredhas occurred

Phenolphthalein is a very common Phenolphthalein is a very common indicator chosenindicator chosen

It undergoes a color change at a It undergoes a color change at a pH of about 7.6pH of about 7.6clear in acid clear in acid Light pink in neutralLight pink in neutralDark pink in baseDark pink in base

Acid–Base TitrationAcid–Base TitrationIn titration, the stand-In titration, the stand-ard is slowly added ard is slowly added to the unknown solnto the unknown soln

As the 2 solns mix, As the 2 solns mix, the acid in one the acid in one neutralizes the base neutralizes the base in the otherin the other

Eventually, enough Eventually, enough standard soln is added standard soln is added to neutralize all of the to neutralize all of the acid or base in the acid or base in the unknown soln.unknown soln.

Indicator changes Indicator changes colorcolor

The point at which this occurs The point at which this occurs is called the equivalence point. is called the equivalence point.

We can calculate the conc from We can calculate the conc from the results of titrationthe results of titration@ the equivalence point the @ the equivalence point the [H[H3300++] = [OH] = [OH--]]

The point at which the indicator The point at which the indicator changes color is called the end changes color is called the end point of the titration.point of the titration.If the indicator is chosen correctly If the indicator is chosen correctly the end point should be very close the end point should be very close to the equivalence point.to the equivalence point.

Procedure for TitrationProcedure for Titration

Therefore, at approximately the Therefore, at approximately the end point of a titration the total mols end point of a titration the total mols of Hof H++ donated by the acid is equal to donated by the acid is equal to the total mols of Hthe total mols of H++ accepted by the accepted by the base.base.We call these molar equivalences We call these molar equivalences (stoichiometric equivalences)(stoichiometric equivalences)

Calculate moles of standard solnCalculate moles of standard solnCalculate moles of unknown Calculate moles of unknown (stoichiometry)(stoichiometry)Claculate conc of unknownClaculate conc of unknown

Procedure for TitrationProcedure for Titration

*Remember: (conc)(vol in L) = moles

*Remember: (conc)(vol in L) = moles

Sample ProblemSample ProblemSolutions of NaOH are used to Solutions of NaOH are used to

unclog drains. unclog drains. A 43.0 ml volume of NaOH was A 43.0 ml volume of NaOH was

titrated with 32.0 ml of .100M HCl. titrated with 32.0 ml of .100M HCl. What is the molar concentration of What is the molar concentration of

the NaOH solution?the NaOH solution?

Sample ProblemSample Problem200 ml of a 0.1 M solution of

sodium hydroxide was needed to neutralize 125 ml of a sulfuric acid

solution. What conc was the sulfuric acid soln?

200 ml of a 0.1 M solution of sodium hydroxide was needed to

neutralize 125 ml of a sulfuric acid solution. What conc was the

sulfuric acid soln?

Titration Practice:Titration Practice:1. Calculate the conc of a nitric acid solution

if a 20 ml sample of the acid required an average vol of 55 ml of a 0.047 M soln of Ba(OH)2 to reach the endpoint of the titration.

2. 15 ml of 12 M Hydrochloric acid is diluted to 250 ml. A 10.0 ml aliquot is measured and titrated with an unknown conc of Potassium hydroxide (vol of 20ml). What is the conc of the hydrochloric acid? What is the conc of the Potassium hydroxide solution?

1. Calculate the conc of a nitric acid solution if a 20 ml sample of the acid required an average vol of 55 ml of a 0.047 M soln of Ba(OH)2 to reach the endpoint of the titration.

2. 15 ml of 12 M Hydrochloric acid is diluted to 250 ml. A 10.0 ml aliquot is measured and titrated with an unknown conc of Potassium hydroxide (vol of 20ml). What is the conc of the hydrochloric acid? What is the conc of the Potassium hydroxide solution?

Titration Curves:Titration Curves:We can also track the titration using a pH meter or indicator paper to record the pHs as we add excess acid or base.If we graph the results, we get a characteristic curve called a titration curve

Graphing pH vs. volume of titrantUsing a titration curve we can determine the equivalence point by analyzing the vertical of the titration curve.

We can also track the titration using a pH meter or indicator paper to record the pHs as we add excess acid or base.If we graph the results, we get a characteristic curve called a titration curve

Graphing pH vs. volume of titrantUsing a titration curve we can determine the equivalence point by analyzing the vertical of the titration curve.

Strong Acid/Base Titration:Strong Acid/Base Titration:

pKa=pH

Weak Acid w/Strong Base:Weak Acid w/Strong Base:

Buffer Region

Polyprotic acid titration:Polyprotic acid titration: