Titrations

Acid-base indicators are… Compounds whose color is sensitive to pH. Indicators are either weak acids or weak bases. For example, weak acid indicators will lose a proton in a base. The deprotonated version displays a different color.

Measuring pH pH paper is a universal indicator. It is made by soaking the paper in several different indicators. A pH meter measures the voltage between two electrodes. The voltage is measured based on the concentration of the hydronium ion.

Phenolphthalein An indicator that changes color from clear in acid to pink in base (pH 8-10). This is the indicator that we will use in the lab!

Titrations The controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration.

Standard Solution The solution that contains the precisely known concentration of a solute is known as a standard solution. The standard solution is often the titrant (it is titrated into the unknown solution)

http://www.dartmouth.edu/~chemlab/techniques/buret.html Read Pg 518-519 in your textbook

Good color! Too much base!

Titration Curve A titration curve is drawn by plotting data attained during a titration, titrant volume on the x-axis and pH on the y-axis. The titration curve serves to profile the unknown solution.

Equivalence Point The point at which the two solutions used in a titration are present in equivalent amounts (moles of acid and base match balanced equation) Amount of acid in moles ≈ Amount of base in moles *Note: this is not the same volume or the same concentration, just the equivalent MOLES

Equivalence Point Strong acid + strong base = equivalence point at pH of 7 Strong acid + weak base = equivalence point at pH of <7 Weak acid + strong base = equivalence point at pH of >7

If we know the molarity and the volume of acid used, then can we calculate the amount of moles of acid? How? MolA = MAVA

How to solve titration problems: Write the balanced neutralization equation Solve for moles of given (using molarity and volume) Convert from moles of given to moles of unknown using mole ratio Use moles of unknown to solve for molarity or volume. If moles are equal, then: MAVA =MBVB

How to solve titration problems: This can be simplified into an equation: MAVA = MBVB cA cB c = moles (coefficient from the balanced neutralization reaction) M = Molarity V = Volume

Worksheet!