Unit A23 4.5 Acid-base equilibria

Question 1

4.5.5 - Making buffer solutions from calculated quantities of salts and acids and determine their pH values using Universal Indicator (UI) paper and a pH meter

Answer 1

• Use a burette to measure out calculated volumes of equimolar solutions of a weak acid and the salt of the weak acid and add to a beaker
• Mix (use a magnetic stirrer)
• Record the pH of the prepared buffer using Universal Indicator paper and a pH meter

Question 2

4.5.6 - Determining the shape of a titration curve by measuring the pH using specialised pH paper or a pH meter for the titration of an acid with a base

Answer 2

• Place acid/base solution of known volume and concentration in a conical flask.
• Record the pH of the solution using a pH meter or narrow range pH paper
• Fill a burette with acid/base of known concentration.
• Add the acid/base in 5 cm3 portions from a burette, mixing with a magnetic stirrer
• Record the pH, after each addition
• Add the acid/base in 1 cm3 portions as the end point approaches
• Continue to add two 5 cm3 portions after the end point
• Plot a graph of pH against volume of solution added (titration curve)

Question 3

4.5.8 - Determining the pH of a variety of salts using pH paper or a pH meter to illustrate the relative strengths of acids and bases

Answer 3

• Prepare solutions of known concentration of a variety of salts
• Record the pH using a pH meter or narrow range pH paper