Practice: A solution of NaOH was prepared in a chemistry lab and the pOH was determined to be 9.3. What is the concentration of OH− ions of this basic solution?
The pH scale is used to determine if a solution is acidic, basic or neutral.
pH Scale
Concept #1: Under standard conditions and concentrations less than 1.0 M, the pH scale ranges from 0 to 14.
Example #1: Given the [H+] of the following solutions, which one is the least acidic?
a) HNO3: [H+] = 1.2 M
b) HCl: [H+] = 0.025 M
c) H2SO4: [H+] = 0.27 M
d) HClO4: [H+] = 0.019 M
Concept #2: The concentrations of H+ and OH– can help determine the pH and pOH of solutions respectively.
Example #2: A solution is prepared by dissolving HCN in 2 L of water. The [H+] was found to equal to 0.34 moles. Calculate the pH of this HCN solution.
Concept #3: Under standard conditions, the addition of pH and pOH is equal to 14.
Example #3: You prepare a solution of HCl with a pH of 2.3 at 25ºC. What would be the pOH and the concentration of hydronium ions of this solution?
Practice: Calculate [OH−] of a lemon juice solution at 25°C with a [H+] = 5.7 × 10−4 M.
Practice: A 345 mL bottle of antacid (Mg(OH)2) contains 1.45 × 10−2 moles of hydroxide ions. Determine pH and pOH of the antacid.
Practice: Which of the following statement(s) on aqueous solutions is/are correct?
a) aqueous solutions have a pH of 7
b) as concentration of hydronium ion increases, concentration of hydroxide ion decreases
c) solutions of weaker acids generally have a higher pOH then solutions of stronger acids
d) pH of pure water equals to 7 at 35º C.
