RP2: Strong Acid–Alkali Titration

A pipette with the appropriate filler delivers a defined aliquot to a conical flask. A burette measures the volume delivered from a change in reading. Follow the approved rinsing and filling method; water remaining in a burette can dilute its solution, and an unfilled tip can cause a misleading first delivery. Read the appropriate meniscus at eye level.

Record both initial and final burette readings, then subtract initial from final to obtain the titre. The burette scale increases downward. The initial reading need not be zero, and a final reading alone is not the volume delivered. Distinguish the precision of the reading from the repeatability of the procedure.

Use a suitable indicator in the specified small amount and a white background to help observe its change. Mix by swirling and approach the endpoint slowly, using dropwise addition near the change. A rough trial can locate the approximate region before careful repeat titrations.

The indicator endpoint is an observable signal chosen to approximate the required chemical condition. Do not assume every indicator works for every acid–base combination. Use the stated concordance rule when selecting repeat titres, retain all raw readings, and avoid averaging an obvious overshoot with careful concordant results merely to increase the number of readings.

Reacting volumes can be determined experimentally without assuming equal concentrations or equal mole ratios. For concentration work, first use the balanced equation and c = n/V with compatible units; 1000 cm³ = 1 dm³. A one-to-one HCl/NaOH example does not justify using equal reacting amounts for every acid.

Concentration calculations may have tier-specific requirements, so use the qualification reference attached to this guide. Extra distilled water added to the conical flask can change the concentration in that flask but not the amount of the original pipetted solute. Distinguish that operation from diluting the stock solution before pipetting.

AQA RP2 requires reacting-volume determination for this separate-science activity. Determining concentration in mol dm⁻³ and g dm⁻³ from the reacting volumes is Higher-tier content. The concentration worked example is labelled for that assessed calculation.

Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.