CPAC 03 Flashcards
1
Q
State the method to find the concentration of hydrochloric acid with sodium hydroxide
A
- wash out 250cm3 volumetric flask with distilled water
- add 25cm3 of hydrochloric acid using pipette into volumetric flask and make solution up to 250cm3 with distilled water
- prepare titration apparatus: burette containing sodium hydroxide and conical flask containing hydrochloric acid solution
- pour 25cm3 aliquot of hydrochloric acid solution into the flask, add 2 drops of phenolphthalein
2
Q
Why does phenolphthalein go back to colourless from pink when left?
A
excess sodium hydroxide reacts with CO2 in air to form sodium carbonate
3
Q
What is the equation for sodium hydroxide with carbon dioxide?
A
2NaOH + CO2 –> Na2CO3 + H2O
4
Q
Are larger or smaller titres better?
A
larger titres are better as there is a smaller percentage uncertainty
