# Chemistry Calculations and Concepts

Determination of the Molar Mass and Ionization Constant of a Weak Monoprotic Acid

Acetic Acid + Water yields Conjugate Base + Hydronium Ion Or HA + H20; H30+ + A-

Calculation of the ionization constant for acetic acid from the measured pH of acetic acid samples:

Acetic Acid titrated with Sodium Hydroxide and the following was determined or known before experiment:

Avg. molar concentration of acetic acid titrated = 0.0455 mol/L

Avg. pH = 3.19

Standardized NaOH = 0.097 mol/L

Mass concentration of acetic acid = 2.4 g/L

Concentration and Ka calculations:

1. Calculation of [H30+] = 10-3.19 = 6.46 X 10-4 ?? - (Is this the way to find the hydronium concentration?)

2. Calculation of [A-] =

3. Calculation of [HA] =

4. Calculation of Ka = [H30+] [A-] =

___________

[HA]

Measurement of the pKa of Acetic Acid by the Half-Neutralization Method

Using half the amount of NaOH required for equilibrium from part 1, the average pH vale was determined to be 4.63

1. Calculation of pKa =

2. Calculation of Ka =

3. Calculation of [H30+] =

4. Calculation of [A-] =

5. Calculation of [HA] =

Molar Mass and Ionization Constant of an Unknown Weak Monoprotic Acid

Unknown acid = 1.84 g/L

NaOH Titrant = 0.097 mol/L

Average pH = 2.60

Avg. molar mass = 0.04252 mol/L

1. Calculation of pKa =

2. Calculation of Ka =

3. Calculation of [H30+] =

4. Calculation of [A-] =

5. Calculation of [HA] =

Problem: OH- concentration of 0.050 M ammonia is 9.5 X 10-4

(a) Write the chemical equation for the dissociation of NH3 in H2O

NH3 + H2O; NH4 + OH-

(b) Equilibrium constant expression for reaction of ammonia with water

Kb = [OH-] [NH4+]

___________

[NH3]

(c) Calculate Kb using the above information

#### Solution Summary

This solution demonstrates how to calculate many chemistry problems such as concentrations and writing chemical equations.