Practicals

Question 1

Describe a practical to make solubls salts from an acid and an insoluble base

Answer 1

MAKING COPPER SULFATE
1) Pour a fixed volume of sulfuric acid into a beaker and place the beaker on top of a bunsen burner and gently heat it until it is almost boiling
2) Using a spatula, place small amounts of copper oxide into the acid and stir using a glass stirring rod
3) Add the copper oxide in EXCESS until you can see the copper oxide collecting at the bottom of the beaker, this means that the reaction is finished and the sulfuric acid has been used up- copper sulfate solution has been formed
4) Filter out the excess copper oxide using a funnel and filter paper

MAKING THE SOLUBLE SALTS
1) Prepare a water bath by placing a beaker of water ontop of a bunsen burner and heating it to a boil
2) Pour the copper sulfate solution into an evaporating basin and place the evaporating basin ontop of the water bath- the steam from the water bath will heat the solution, continue to heat the solution until only half of the solution remains
3) Then place the evaporating basin in a cool place to allow the solution to cool and the salt crystals to form
4) Then, pat the salt crystals dry using filter paper

Question 2

Why is the sulfuric acid heated in the beginning of this practical?

[1 mark]

Answer 2

To increase the rate of the reaction

Question 3

How would you know when copper oxide is in excess in this practical

[1 mark]

Answer 3

There is a black solid visible

Question 4

Why do crystals form when the copper sulfate solution is cooled?

[1 mark]

Answer 4

The solubility of the salt crystals decreases when the temperature decreases

Question 5

Describe a practical to determine the reacting volumes of colutions of a strong acid and a strong alkali using titration

Answer 5

1) Use a pipette to transfer 25cm³ of sodium hydroxide alkali into a conical flask
2) Add 5 drops of pink PHENOLPHTHLANEIN indicator into the conical flask and place a white tile underneath the flask so that the colour change will be bclear
3) Fill a burette with sulfuric acid
4) Add the acid to the alkali until there is a slight colour change
5) Now use the burette to add the acid to the alkali drop by drop until the solution is neutral and the phenolphthalein indicator has changed colour from pink to colourless
6) Now read the volume of acid added using the burette
7) Repeat the experiment three times until you have concordant results, then calculate a mean volume of acid required to neutralise the alkali

Question 6

Describe a practical to investigate what happens when an aqueous solution is electrolysed by two inert electrodes

Answer 6

1)Using a measuring cylinder, pour 50cm³ of copper (II) chloride solution into a beaker
2)Place a plastic petri dish with two holes in it on top of the beaker, then insert two inert graphite rods into the holes (the elctrodes)
3)Then attatch crocodile clips to the electrodes and connect them to a terminal with a low-voltage power pack.
4)Turn the power pack to 4V and switch it on
5)You will see brown copper solid beginning to coat the cathode and bubbles of chlorine gas at the anode
6)Hold damp blue litmus paper next to the anode and it will bleach, this proves that the bubbles are hydrogen gas
7)Now repeat the solution with sodium chloride