Making sodium, potassium and ammonium salts
3 marks · NormalExplain the role of methyl orange indicator in an acid–alkali titration to prepare a sodium salt. Why does the indicator colour change at the endpoint, and how does this help determine when the reaction is complete?
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
Also accept: Indicator turns orange at endpoint, showing neutralisation is nearly complete
Common mistakes: Says indicator detects type of salt; Says indicator turns green
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States that methyl orange is used to show the endpoint of the reaction.
B2 · 1 mark · Explains indicator changes colour (from yellow to orange or to red) at endpoint of neutralisation.
B3 · 1 mark · Explanation of how the colour change lets you know when enough acid has been added to neutralise the alkali.
Worked solution
Methyl orange is added to the alkali before titrating. It is yellow in alkali, and as acid is added, the solution changes to orange near neutralisation. The orange colour signals the endpoint, showing you when enough acid has been added to neutralise the alkali. This means the correct amount of acid and alkali have reacted, allowing you to prepare a pure sodium salt.