Sample Problem 8.1 Dissociation of an Arrhenius Base Write the equation for the dissociation of Ca(OH)2(s) in water. Solution The base Ca(OH)2 dissociates in water to give a solution of calcium ions (Ca2+) and twice as many hydroxide ions (OH-). Study Check 8.1 Write the equation for the dissociation of lithium hydroxide in water.

Sample Problem 8.2 Acids and Bases In each of the following equations, identify the reactant that is a Brønsted–Lowry acid and the reactant that is a Brønsted–Lowry base: a. HBr(aq) + H2O(l) → H3O+(aq) + Br–(aq) b. Solution a. HBr, acid; H2O base b. Acid H2O, acid; CN–, base Study Check 8.2 When HNO3 reacts with water, water acts as a base (H+ acceptor). Write the equation for the reaction.

Sample Problem 8.3 Identifying Conjugate Acid–Base Pairs Identify the conjugate acid–base pairs in the following reaction: HBr(aq) + NH3(aq) → Br(aq) + NH4+(aq) Solution In the reaction, the acid HBr donates H+ to the base NH3. The conjugate acid–base pairs are HBr/Br and NH4+/NH3. Study Check 8.3 In the following reaction, identify the conjugate acid–base pairs:

Sample Problem 8.4 Calculating the [H3O+] of a Solution A vinegar solution has a [OH–] = 5.0  10–12 M at 25 C. What is the of the [H3O+] vinegar solution? Is the solution acidic, basic, or neutral? Solution Step 1 Write the Kw for water. Step 2 Solve the Kw for the unknown [H3O+]. Rearrange the ion product expression by dividing through by the [OH–] Step 3 Substitute in the known [OH–]and calculate. Because the [H3O+] of 2.0  103 M is larger than the [OH–] of 5.0  1012 M, solution is acidic. Study Check 8.4 What is the [H3O+] of an ammonia cleaning solution with [OH–] = 4.0  104 M? Is the solution acidic, basic, or neutral?

Sample Problem 8.5 Calculating pH Using the [H3O+] Determine the pH for the following solutions: a. [H3O+] = 1.0  105 M b. [H3O+] = 5  108 M Solution a. Step 1 Enter the [H3O+]. Step 2 Press the log key and change the sign. Step 3 Adjust the number of SFs on the right of the decimal point to equal the SFs in the coefficient.

Sample Problem 8.5 Calculating pH Using the [H3O+] Continued b. Step 1 Enter the [H3O+]. Step 2 Press the log key and change the sign. Step 3 Adjust the number of SFs on the right of the decimal point to equal the SFs in the coefficient. Study Check 8.5 What is the pH of bleach with [H3O+] = 4.2  10-12 M?

Sample Problem 8.6 Calculating pH Using the [OH] What is the pH of an ammonia solution with [OH] = 3.7  103 M? Solution Step 1 Enter the [H3O+]. Because [OH] is given for the ammonia solution, we have to calculate [H3O+] using the Kw. When we divide through by the [OH], we obtain the [H3O+]. Step 2 Press the log key and change the sign. Step 3 Adjust the number of SFs on the right of the decimal point to equal the SFs in the coefficient. Study Check 8.6 Calculate the pH of a sample of acid rain with [OH] = 2  1010 M.

Sample Problem 8.7 Calculating [H3O+] from pH Determine the for solutions having each of the following pH values: a. pH = 3.0 b. pH = 8.2 Solution a. For pH values that are whole numbers, the [H3O+] can be written 1  10–pH. b. For pH values that are not whole numbers, the [H3O+] is calculated as follows: Step 1 Enter the pH value and press the change sign key. Step 2 Convert –pH to concentration. Press the 2nd function key and then the 10x key. Or press the inverse key and then the log key. Step 3 Adjust the significant figures in the coefficient. Because the pH value of 8.2 has one digit on the right of the decimal point, the [H3O+] is written with one significant figure. [H3O+] = 6  109 M

Sample Problem 8.7 Calculating [H3O+] from pH Continued Study Check 8.7 What is the [H3O+] of a beer that has a pH of 4.5?

Sample Problem 8.8 Balancing Equations of Acids Write the balanced equation for the neutralization of HCl(aq) and Ba(OH)2(s). Solution Step 1 Write the reactants and products. HCl(aq) + Ba(OH)2(s) → salt + H2O(l) Step 2 Balance the H+ in the acid with the OH– in the base. Placing a coefficient of 2 in front of HCl provides 2H+ for the 2OH– in Ba(OH)2. 2HCl(aq) + Ba(OH)2(s) → salt + H2O(l) Step 3 Balance the H2O with the H+ and the OH–. Use a coefficient of 2 in front of H2O to balance 2H+ and 2OH–. 2HCl(aq) + Ba(OH)2(s) → salt + 2H2O(l) Step 4 Write the salt from the remaining ions. Use the ions Ba2+ and 2Cl– to write the formula of the salt, BaCl2. 2HCl(aq) + Ba(OH)2(s) → BaCl2(aq) + 2H2O(l) Study Check 8.8 Write the balanced equation for the reaction between H2SO4(aq) and NaHCO3(aq).

Sample Problem 8.9 Titration of an Acid A 25.0-mL (0.025 L) sample of HCl solution is placed in a flask with a few drops of phenolphthalein (indicator). If 32.6 mL of a 0.185 M NaOH solution is needed to reach the endpoint, what is the molarity of the HCl solution? NaOH(aq) + HCl(aq)→NaCl(aq) + H2O(l) Solution Step 1 State the given and needed quantities. Given 25.0 mL (0.025 L) of a HCl solution; 32.6 mL of a 0.185 M NaOH solution Need molarity of HCl solution Step 2 Write a plan to calculate molarity. Step 3 State equalities and conversion factors including concentration.

Sample Problem 8.9 Titration of an Acid Continued Step 4 Set up the problem to calculate the needed quantity. Study Check 8.9 What is the molarity of a HCl solution, if 28.6 mL of a 0.175 M NaOH solution is needed to neutralize a 25.0-mL sample of the HCl solution?