AC19: Neutralisation Flashcards
What is the equivalence point of a titration
the volume of one solution that reacts exactly with the volume of another according to the stoichiometry of the reaction
How do you identify the pH of a reaction using a pH curve
pH is the midpoint of the vertical section of the pH curve at the equivalence point
What is the pH of a reaction between a strong acid and strong base, using a pH curve
7
What is the pH of a reaction between a strong acid and weak base, using a pH curve
<7
What is the pH of a reaction between a weak acid and strong base, using a pH curve
> 7
Why does the pH curve of a weak acid and strong base, become less steep at the start
because the alkali reacts with the weak acid to form a buffer solution that minimises the change in pH
What is the pH of a reaction between a weak acid and weak base, using a pH curve
pH at equivalence point depends on relative strength of acid and base
What is an indicator
A weak acid (Hln) that has a different colour to its conjugate base (ln⁻)
What is the pH range of an indicator
±1 of its pKa
Explain how methyl orange acts as an indicator
methyl orange is red and has a different colour to its conjugate base (yellow). At the end point of the titration, when indicator contains equal [HA] and [A⁻], the end point colour = orange
Explain how you choose an acid-base indicator
You choose an indicator where the colour change (endpoint) coincides with the vertical section of the pH curve
Why is it important to choose the correct indicator for a titration
Different indicators have different Ka and pKa values and so change colour over different pH ranges
