Core Practical: Acid-Alkali Titration Flashcards

All 6 cards in this deck

What are the steps to carry out an accurate acid–alkali titration?

e.g. finding the volume of dilute hydrochloric acid needed to neutralise $25.0\ \mathrm{cm^3}$ of sodium hydroxide solution

1. Use a pipette to transfer $25.0\ \mathrm{cm^3}$ of alkali into a conical flask and add a few drops of indicator
2. Add acid from a burette, swirling the flask over a white tile, dropwise near the end point, until the indicator just changes colour
3. Repeat until titres are concordant (within $0.20\ \mathrm{cm^3}$) and calculate the mean titre

In a titration, what colour change does phenolphthalein show when acid is added to an alkali?

Pink $\rightarrow$ colourless.

In a titration, what colour change does methyl orange show when acid is added to an alkali?

Yellow $\rightarrow$ orange (red in excess acid).

What makes titration titres concordant, and what are they used for?

Titres within $0.20\ \mathrm{cm^3}$ of each other; they are used to calculate the mean titre.

True or false? Water left in the conical flask after rinsing makes the titre too low.

False. The amount of alkali in the flask is unchanged, so there is no effect on the titre.

How should a solution of accurately known concentration be prepared for a titration?

Dissolve the solid in distilled (deionised) water and make the solution up to the mark in a volumetric flask, e.g. $250\ \mathrm{cm^3}$ in total.