Prac 9

Question 1

Required Practical 9 Measuring pH for Weak Acid vs Weak

Answer 1

Calibrate pH meter using buffer solutions

Add 25 cm³ of your chosen alkali to a conical flask

Measure initial pH of the alkali
Add acid in 1 cm³ amounts using a titration burette

Stir mixture to equalize the pH
Measure and record the pH to 1 dp

When approaching endpoint, add smaller volumes of acid

Add acid until in excess

Draw a graph of pH vs volume of acid added

Question 2

Calibrate pH meter using buffer solutions. Why?

Answer 2

pH meters lose accuracy over time due to a change in characterists. They are calibrated against buffers with a known pH value.

Question 3

Suitable indicators for each type of titration?

Answer 3

Phenopthalein: pink to colourless in acid
Used for Strong base titrations

Methyl Orange: orange to red in acid
Used for Strong acid titrations

Ph probe: for weak bases/acids

Suitable as it has a pH range within the vertical line/steep point of the curve.