Chemistry

Objectives

1. To understand the importance of choosing a right indicator for detecting the end point of an

acid-base titration.

2. To determine the titration curve for acid-base titration.

Materials

Chemicals

0.1 M hydrochloric acid, 0.1M acetic acid, 0.1M sodium hydroxide, 0.1M ammonium hydroxide, phenolphthalein, screened methyl orange and methyl orange.

Apparatus

100mL beakers, 250mL conical flask, 50mL burettes, 25mL pipettes, pipette fillers, funnel, pH meters, magnetic stirrer

Methods

Part 1: Suitability of Indicators

A. Strong Acid- Weak Base Titration

1. 0.1M of ammonium hydroxide was filled in a burette using a funnel.

2. 25mL of 0.1M hydrochloric acid was pipette into a 250mL conical flask.

3. 2-3 drops of the indicator, phenolphthalein is added into the solution in the conical flask.

4. The titration was performed and the end point is determined when the colour of the solution

changed from colourless to pink.

5. The result was presented in Table I.

6. Step 1-5 were repeated using methyl orange as indicator. The colour changed from orange to

yellow indicates it’s end point.

7. The result is presented in Table II.

8. The titration was repeated until at least two titre values are within 0.2mL of each other

9. However, it is advised not to proceed to further titrations if the indicator does not change colour

after 50mL of titrant has been added in the first titration.

B. Weak Acid-Strong Base Titration

1. 0.1M of sodium hydroxide was filled in a burette using a funnel.

2. 25mL of 0.1M acetic acid was pipette into a 250mL conical flask.

3. 2-3 drops of indicator, phenolphthalein was added into the solution in the conical flask.

4. The titration was performed and the end point was determined when the colour of the solution

change from colourless to pink.

5. The result was presented in Table III.

6. Step 1-5 were repeated using methyl orange as indicator. The colour changes from orange to

yellow indicates...