The equilibrium concentrations are inserted into the reaction quotient expression, and
the equilibrium constant is calculated.Comments
Any equilibrium may be used, as long as one substance is colored.Experiment 11: pH Measurements and Indicators for
Acid–Base Titrations
Synopsis
The acidity of various substances is determined with a pH meter or acid–base indicators.
This may also be done by mixing or diluting solutions. (See the Equilibrium chapter.)Equipment
analytical balance Erlenmeyer flask graduated cylinder
pH meter pipet volumetric flaskMeasurements- Weigh each acid or base into a volumetric flask, and dilute to volume.
- Pipet a sample of an acid or base of known concentration into a volumetric flask, and
dilute to volume. - Pipet dififferent solutions into a flask.
- Measure the pH of the solutions using a pH meter.
Calculations
All weighed samples are converted to moles by using the molar mass, and the moles are
divided by the volume of the volumetric flask in liters to yield molarity.
The concentrations of the diluted solutions (measurement 2) are calculated by using
the dilution equation.
The concentrations of the other solutions (measurement 3) are calculated from the
balanced chemical equation and the dilution equation.
The pH may be estimated by adding an acid–base indicator to any of the prepared
solutions.
The hydrogen ion concentration, hydroxide ion concentration, or pOH may be calculated
from the pH. One or more of these may be used to determine the concentration of all other
species in the solution.Comments
The original acids and bases may all be solids or solutions, or a mixture of both.Experiment 12: The Rate and Order of a Reaction
Synopsis
The rate equation for a reaction is determined in this experiment. Known quantities of
solutions are mixed, and the time required for a change is recorded. (See the Kinetics
chapter.)290 Step 4. Review the Knowledge You Need to Score High