Titrations

Question 1

(1) ) What type of reaction takes place when hydrochloric acid reacts with sodium
hydroxide solution?

Answer 1

neutralisation

Question 2

(1) Suggest why universal indicator must not be used in titration experiments

Answer 2

no {sharp/clear/distinct}
change in colour
• gradual colour change
• there are too many different
colours

Question 3

(6) Describe a titration experiment to find the exact volume of hydrochloric acid
needed to neutralise 25.0 cm3
of sodium hydroxide solution and how you would
use this result to obtain pure, dry crystals of sodium chloride.

Answer 3

titration experiment
• rinse pipette with alkali and burette with acid
• measure alkali using a pipette
• into suitable container e.g. flask/beaker
• add a few drops of indicator / suitable named indicator (eg
methyl orange/phenolphthalein)
• flask on a white tile
• fill burette with acid
• read level/volume (of acid) in burette
• add acid from burette to the flask slowly / swirl the flask
• until {indicator just changes colour/correct colour change for
named indicator (eg methyl orange yellow to peach/orange,
phenolphthalein pink to colourless)/solution is neutral}
• read level/volume (of acid) in burette
• repeat experiment
• until concordant results

salt preparation
• mix the same volume of alkali with the volume of acid
determined from the first experiment but do not add
indicator (or add (activated) charcoal to remove indicator,
then filter)
• pour solution into an evaporating basin
• {heat solution/leave the water to evaporate} until pure salt
crystals are left

Question 4

(1) When sodium hydroxide solution is titrated with dilute hydrochloric acid, an acid-base
indicator is used.

Answer 4

methyl orange,

phenolphthalein

Question 5

(1) The hydrochloric acid is added from a burette to the sodium hydroxide solution in
a conical flask.
At the end point the indicator changes colour.
State the colour change for this indicator at the end point. (from and to)

Answer 5

methyl orange :
yellow  orange/pink/red
phenolphthalein :
magenta/pink  colourless

Question 6

(2) Describe how you would measure out and transfer 25.0 cm3 of the solution of
the alkali.

Answer 6

pipette (1)
 one practical point eg draw
liquid up to line/ use
pipette filler/ rinse first /
read at eye level (1)