Loose Ends from Bell Work An acidic solution makes the color of pH paper turn ___________________, while a basic solution makes the color of pH paper turn ________________. The indicator _________________________ is used to study neutralizations of weak acids with strong bases. Red Blue phenolphthalein

Titrations

What is a titration? An experiment used to determine the concentration of an unknown by using a known amount of a solution with a known molarity. An experiment used to determine the concentration of an unknown by using a known amount of a solution with a known molarity. The most common use is determining concentrations of unknown acids. The most common use is determining concentrations of unknown acids.

Titration Terms Equivalence Point – the point at which the two solutions used in the titration are present in chemically equivalent amounts. Equivalence Point – the point at which the two solutions used in the titration are present in chemically equivalent amounts. Standard Solution – a solution of known concentration Standard Solution – a solution of known concentration Titrant – A solution of known concentration that is used to titrate a solution of unknown concentration Titrant – A solution of known concentration that is used to titrate a solution of unknown concentration

Titration Curve

Finding a Suitable Indicator Every indicator has a transition range, the pH range through which an indicator changes color Every indicator has a transition range, the pH range through which an indicator changes color The indicator selected must change at the appropriate time during the titration. The indicator selected must change at the appropriate time during the titration. The instant at which the indicator changes color is the end point of the titration. The instant at which the indicator changes color is the end point of the titration. If the proper indicator was selected, the end point and equivalence point will be the same. If the proper indicator was selected, the end point and equivalence point will be the same.

Calculations The most important relationship deals with molarity. The most important relationship deals with molarity. Remember M = n/V Remember M = n/V Where M = concentration (mol/L), n = moles, and V = volume in L Where M = concentration (mol/L), n = moles, and V = volume in L The resulting formula: The resulting formula: # H+ M acid V acid = # OH- M base V base # H+ M acid V acid = # OH- M base V base

Examples If 20.6 mL of M aqueous HCl is required to titrate 30.0 mL of an aqueous solution of NaOH to the equivalence point, what is the molarity of the NaOH solution? If 20.6 mL of M aqueous HCl is required to titrate 30.0 mL of an aqueous solution of NaOH to the equivalence point, what is the molarity of the NaOH solution? In the titration of 35.0 mL of drain cleaner that contains NaOH, mL of M H 2 SO 4 must be added to reach the equivalence point. What is the concentration of the base of the cleaner? In the titration of 35.0 mL of drain cleaner that contains NaOH, mL of M H 2 SO 4 must be added to reach the equivalence point. What is the concentration of the base of the cleaner?