5 Steps to a 5 AP Chemistry

286  Step 4. Review the Knowledge You Need to Score High

Experiment 6: Standardization of a Solution

Synopsis

The concentration of a solution is determined by titration with a sample of known composition.

(See the Stoichiometry chapter.)

Equipment

analytical balance buret desiccator

drying oven Erlenmeyer flask pH meter

pipet support stand volumetric flask

wash bottle clamp

Refer to figure 19.3 for general titration set-up.

Measurements

1.the mass of an empty flask

2.the mass of the flask plus the sample

3.the initial reading of the buret

4.intermediate readings from the buret

5.the final reading of the buret

6.the pH of the solution at various times during the reaction

Calculations

The mass of the sample is calculated from the differences between masses 1 and 2. The

volume added is calculated by taking the difference between measurement 3 and either

measurement 4 or 5.

A plot of pH versus the volume added is made. This graph or the difference between

measurements 3 and 5 gives the volume of titrant.

The volume of titrant is converted to liters.

The mass of the sample is converted to moles by using the molar mass. The moles of titrant

may be calculated from a consideration of the moles of sample and the balanced chemical equa-

tion. The moles of titrant divided by the liters of solution gives the molarity of the solution.

Comments

A solution could be prepared by dissolving a known amount of solute in a volumetric flask

and diluting to volume.

The course of the titration could be followed with an acid–base indicator instead of a

pH meter.

Experiment 7: Acid–Base Titration

Synopsis

The concentration of an acid or a base may be determined by titrating a solution of an

unknown concentration with a solution of a known concentration. (See the chapter on

Reactions and Periodicity and the chapter on Stoichiometry.)

Equipment

analytical balance buret clamp

desiccator drying oven Erlenmeyer flask

pH meter pipet support stand

wash bottle