Required practical - Separating mixtures

Question 1

what is the aim of the practical

Answer 1

produce a pure, dry sample of a soluble salt from an insoluble oxide or carbonate.

Question 2

Preparation

Answer 2

­­Use a Bunsen burner to gently warm the acid.
Add the insoluble solid (with stirring) until the reaction no longer happens.

Filtration - Filter the solution to remove the excess insoluble solid.
This will leave a solution of the salt dissolved in water.

Crystallisation - Heat the solution in an evaporating basin above a beaker of water.
The ‘water bath’ ensures gentle heating.
Let the solution cool and allow more water to evaporate.
As water evaporates, the solution will become more concentrated and the salt will begin to crystallise.

Question 3

how to make a soluble salt using an acid

Answer 3

1. start with a fixed amount of your dilute acid, and heat it in a beaker above a heatproof mat until its almost boiling
2. using a spatula, add small amounts of the base to the acid, and stir with a glass rod
3. the base will react and seem to disappear
   - continue adding more of the base in excess if you dont get the right colour
   - stop adding the base if powder still remains after stirring
4. at this point the reaction has stopped, as all of the acid has reacted
5. Use a filter funnel and filter paper to remove the unreacted base
6. Take the solution and place it in an evaporating basin
7. heat it gently over a water bath
8. heat it until half of the solution remains
9. leave the solution for 24 hours in a cool place for crystals to form
10. scrape the crystals onto a paper towel and gently pat dry

Question 4

why do we need to make sure all of the acid reacts

Answer 4

if theres any left at the end, it would contaminate our salt

Question 5

why do we wait until the acid is almost boiling, not actually boiling

Answer 5

because it could bubble over when we add our other reactant ,and that would be dangerous