Ionic Equilibria: Acids and Bases Chapter 18 Ionic Equilibria: Acids and Bases

A Review of Strong Electrolytes The calculation of ion concentrations in solutions of strong electrolytes is easy. Example 18-1: Calculate the concentrations of ions in 0.050 M nitric acid, HNO3.

A Review of Strong Electrolytes Example 18-2: Calculate the concentrations of ions in 0.020 M strontium hydroxide, Sr(OH)2, solution.

The Autoionization of Water Example 18-3: Calculate the concentrations of H3O+ and OH- in 0.050 M HCl.

The Autoionization of Water Use the [H3O+] and Kw to determine the [OH-].

The pH and pOH scales If either the [H3O+] or [OH-] is known, the pH and pOH can be calculated. Example 18-4: Calculate the pH of a solution in which the [H3O+] =0.030 M.

The pH and pOH scales Example 18-5: The pH of a solution is 4.597. What is the concentration of H3O+?

The pH and pOH scales Example 18-6: Calculate the [H3O+], pH, [OH-], and pOH for a 0.020 M HNO3 solution. Is HNO3 a weak or strong acid? What is the [H3O+] ?

The pH and pOH scales Example 18-6: Calculate the [H3O+], pH, [OH-], and pOH for a 0.020 M HNO3 solution.

The pH and pOH scales Example 18-7: Calculate the number of H3O+ and OH- ions in one liter of pure water at 250C.

Ionization Constants for Weak Monoprotic Acids and Bases Example 18-8: Write the equation for the ionization of the weak acid HCN and the expression for its ionization constant.

Ionization Constants for Weak Monoprotic Acids and Bases Example 18-9: In a 0.12 M solution of a weak monoprotic acid, HY, the acid is 5.0% ionized. Calculate the ionization constant for the weak acid.

Ionization Constants for Weak Monoprotic Acids and Bases Since the weak acid is 5.0% ionized, it is also 95% unionized. Calculate the concentration of all species in solution.

Ionization Constants for Weak Monoprotic Acids and Bases Use the concentrations that were just determined in the ionization constant expression to get the value of Ka.

Ionization Constants for Weak Monoprotic Acids and Bases Example 18-10: The pH of a 0.10 M solution of a weak monoprotic acid, HA, is found to be 2.97. What is the value for its ionization constant? pH = 2.97 so [H+]= 10-pH

Ionization Constants for Weak Monoprotic Acids and Bases Use the [H3O+] and the ionization reaction to determine concentrations of all species.

Ionization Constants for Weak Monoprotic Acids and Bases Calculate the ionization constant from this information.

Ionization Constants for Weak Monoprotic Acids and Bases Example 18-11: Calculate the concentrations of the various species in 0.15 M acetic acid, CH3COOH, solution. It is always a good idea to write down the ionization reaction and the ionization constant expression.

Ionization Constants for Weak Monoprotic Acids and Bases Next, combine the basic chemical concepts with some algebra to solve the problem.

Ionization Constants for Weak Monoprotic Acids and Bases Next we combine the basic chemical concepts with some algebra to solve the problem

Ionization Constants for Weak Monoprotic Acids and Bases Next we combine the basic chemical concepts with some algebra to solve the problem

Ionization Constants for Weak Monoprotic Acids and Bases Substitute these algebraic quantities into the ionization expression.

Ionization Constants for Weak Monoprotic Acids and Bases Solve the algebraic equation, using a simplifying assumption that is appropriate for all weak acid and base ionizations.

Ionization Constants for Weak Monoprotic Acids and Bases Solve the algebraic equation, using a simplifying assumption that is appropriate for all weak acid and base ionizations.

Ionization Constants for Weak Monoprotic Acids and Bases Complete the algebra and solve for the concentrations of the species.

Ionization Constants for Weak Monoprotic Acids and Bases Note that the properly applied simplifying assumption gives the same result as solving the quadratic equation does.

Ionization Constants for Weak Monoprotic Acids and Bases

Ionization Constants for Weak Monoprotic Acids and Bases Let us now calculate the percent ionization for the 0.15 M acetic acid. From Example 18-11, we know the concentration of CH3COOH that ionizes in this solution. The percent ionization of acetic acid is

Ionization Constants for Weak Monoprotic Acids and Bases Example 18-12: Calculate the concentrations of the species in 0.15 M hydrocyanic acid, HCN, solution. Ka= 4.0 x 10-10 for HCN

Ionization Constants for Weak Monoprotic Acids and Bases

Ionization Constants for Weak Monoprotic Acids and Bases The percent ionization of 0.15 M HCN solution is calculated as in the previous example.

Ionization Constants for Weak Monoprotic Acids and Bases Example 18-13: Calculate the concentrations of the various species in 0.15 M aqueous ammonia.

Ionization Constants for Weak Monoprotic Acids and Bases

Ionization Constants for Weak Monoprotic Acids and Bases The percent ionization for weak bases is calculated exactly as for weak acids.

Ionization Constants for Weak Monoprotic Acids and Bases Example 18-14: The pH of an aqueous ammonia solution is 11.37. Calculate the molarity (original concentration) of the aqueous ammonia solution.

Ionization Constants for Weak Monoprotic Acids and Bases

Ionization Constants for Weak Monoprotic Acids and Bases Use the ionization equation and some algebra to get the equilibrium concentration.

Ionization Constants for Weak Monoprotic Acids and Bases Substitute these values into the ionization constant expression.

Ionization Constants for Weak Monoprotic Acids and Bases Examination of the last equation suggests that our simplifying assumption can be applied. In other words (x-2.3x10-3) ≈ x. Making this assumption simplifies the calculation.

Polyprotic Acids Example 18-15: Calculate the concentration of all species in 0.100 M arsenic acid, H3AsO4, solution. Write the first ionization step and represent the concentrations. Approach this problem exactly as previously done.

Polyprotic Acids Substitute the algebraic quantities into the expression for Ka1.

Polyprotic Acids Use the quadratic equation to solve for x, and obtain both values of x.

Polyprotic Acids Next, write the equation for the second step ionization and represent the concentrations.

Polyprotic Acids Substitute the algebraic expressions into the second step ionization expression.

Polyprotic Acids

Polyprotic Acids Finally, repeat the entire procedure for the third ionization step.

Polyprotic Acids Substitute the algebraic representations into the third ionization expression.

Polyprotic Acids Use Kw to calculate the [OH-] in the 0.100 M H3AsO4 solution.

Salts of Strong Bases and Weak Acids Example 18-16: Calculate the hydrolysis constants for the following anions of weak acids. The fluoride ion, F-, the anion of hydrofluoric acid, HF. For HF, Ka=7.2 x 10-4.

Salts of Strong Bases and Weak Acids The cyanide ion, CN-, the anion of hydrocyanic acid, HCN. For HCN, Ka = 4.0 x 10-10. You do it!

Salts of Strong Bases and Weak Acids Example 18-17: Calculate [OH-], pH and percent hydrolysis for the hypochlorite ion in 0.10 M sodium hypochlorite, NaClO, solution. “Clorox”, “Purex”, etc., are 5% sodium hypochlorite solutions.

Salts of Strong Bases and Weak Acids Set up the equation for the hydrolysis and the algebraic representations of the equilibrium concentrations.

Salts of Strong Bases and Weak Acids Substitute the algebraic expressions into the hydrolysis constant expression.

Salts of Strong Bases and Weak Acids Substitute the algebraic expressions into the hydrolysis constant expression.

Salts of Strong Bases and Weak Acids The percent hydrolysis for the hypochlorite ion may be represented as:

Salts of Weak Bases and Strong Acids Example 18-18: Calculate [H+], pH, and percent hydrolysis for the ammonium ion in 0.10 M ammonium bromide, NH4Br, solution. Write down the hydrolysis reaction and set up the table as we have done before:

Salts of Weak Bases and Strong Acids Substitute the algebraic expressions into the hydrolysis constant.

Salts of Weak Bases and Strong Acids Complete the algebra and determine the concentrations and pH.

Salts of Weak Bases and Strong Acids The percent hydrolysis of the ammonium ion in 0.10 M NH4Br solution is:

Hydrolysis of Small Highly-Charged Cations Example 18-19: Calculate the pH and percent hydrolysis in 0.10 M aqueous Be(NO3)2 solution. The equation for the hydrolysis reaction and representations of concentrations of various species are:

Hydrolysis of Small Highly-Charged Cations Algebraic substitution of the expressions into the hydrolysis constant:

Hydrolysis of Small Highly-Charged Cations Calculate the percent hydrolysis of Be2+.

Synthesis Question Rain water is slightly acidic because it absorbs carbon dioxide from the atmosphere as it falls from the clouds. (Acid rain is even more acidic because it absorbs acidic anhydride pollutants like NO2 and SO3 as it falls to earth.) If the pH of a stream is 6.5 and all of the acidity comes from CO2, how many CO2 molecules did a drop of rain having a diameter of 6.0 mm absorb in its fall to earth?

Synthesis Question

Synthesis Question