Planning (Example)

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Question: You are given 3 solutions of hydrochloric acid (A1, A2 and A3). Design an experiment to determine which is the most and least concentrated acid.

 

Procedure:

1. Fill up burette with 0.1 mol/dm³ NaOH.
2. Pipette 25.0 cm³ of A1 into a conical flask.
3. Add 2-3 drops of methyl orange indicator into solution in conical flask.
4. Titrate against NaOH until the solution turns from red to orange. Record the volume of NaOH used.
5. Repeat steps 1-3 with A2 and A3.

 

Results & Discussion:

 

Acid	Volume of NaOH/ cm3
A1
A2
A3

• For a fixed volume of acid (25.0 cm³), the more concentrated acid will contain a larger number of moles of HCl, hence will require a larger number of moles of NaOH for neutralisation.
• Since the concentration of NaOH is kept constant (0.1 mol/dm³), the more concentrated acid will require a larger volume of NaOH to reach end-point.

 

Conclusion:

• The most concentrated acid is ____ because it required the largest volume of NaOH for neutralisation.
• The least concentrated acid is ____ because it required the smallest volume of NaOH for neutralisation.