Chemistry practical 3

Question 1

Aim of this

Answer 1

Find concentration of a solution of HCl

Question 2

How to prepare the solution of hydrochloric acid

Answer 2

Rinse out a volumetric flask with deionised water
Use pipette to transfer 25cm3 of HCl solution
Make up to the mark with deionised water by diluting the acid

Question 3

Step 1 of titration

Answer 3

Wash conical flask with deionised water
Transfer 25cm3 aliquot of HCl into a conical flask + 2 drops of phenolphthalein indicator

Question 4

Step 2 of titration

Answer 4

Titrate contents of previously standardised NaOH solution against HCl
Whilst stirring, so colour change of pink persists for 5 seconds or more

Question 5

Colour change of indicator

Answer 5

Colourless (in acid) to pink

Question 6

Why will the colour pink fade over time?

Answer 6

Because the excess sodium hydroxide reacts with carbon dioxide in air to form sodium carbonate
Thus pH decreases causing colour change back to colourless

Question 7

If sodium hydroxide stored reacts with CO2 how does that change concentration of CO2?

Answer 7

Will decrease it