Science Revision Pack Number 5 Pause the video at any point if you want to answer the questions.

Electrolysis uses electrical energy to break down (decompose) chemicals into simple chemicals. We can use electrolysis to split up hydrochloric acid into hydrogen and chlorine. Hydrogen is used as a fuel in cars and rockets. Chlorine is used to kill bacteria in water. Electrolysis of hydrochloric acid must be done in a fume cupboard because chlorine is produced. Chlorine is a toxic (poisonous) gas.

Questions 1. What fuel is used in cars and rockets? A. Hydrogen 2. What type of energy does electrolysis use? A. Electrical

How can we test for important chemicals? We can test for hydrogen by using flame test. Hydrogen makes a pop sound when heated. We can test for chlorine using dump blue litmus paper. When it touches chlorine, blue litmus paper turns red and then white. Chlorine bleaches the litmus paper white. We can test for carbon dioxide gas by using limewater test. Clear limewater turns milky when carbon dioxide is bubbled through it.

Questions 1. What sound does Hydrogen make when heated? A. ‘Pop’ 2. What does Carbon Dioxide do to limewater? A. Turns it milky coloured

We can use the flame test to see what metal a compound has in it. When copper burns, it makes blue green flame. When sodium burns, it makes yellow flame. When potassium burns, it makes red-pink (lilac) flame. You need to clean wire all the time before testing for metals to avoid contamination.

Questions 1. What colour flame does copper produce? A. Blue/Green 2. Why do we need to clean wire before we use it to test? A. To avoid contamination

universal indicator - pH scale We can use the universal indicator to test for the acids. The yellow universal indicator changes colour depending on pH of a chemical. Red colour indicates strong acid with pH 1.

Questions 1. Is a PH of 1 (red) an Acid or an Alkali? A. Acid 2. What colour would show ‘neutral’? A. Green

sulphuric acid + copper oxide → copper sulphate + water When an acid reacts with an alkali (base), a chemical reaction called neutralisation takes place. The new products are neutral. They are water and salt. The name of the salt has its first name taken from the metal in alkali and second name after acid. Example: sulphuric acid + copper oxide → copper sulphate + water See the instructions of how we carried out this reaction on next page.

Questions 1. When an acid reacts with an alkali, what process takes place? A. Neutralisation 2. What two things are left behind? A. Salt and Water

How to neutralise sulphuric acid by reacting it with copper oxide (making of copper sulphate salt). Warm up 20ml of sulphuric acid for one minute. (Bunsen burner, mat, tripod, gauze, tongues, beaker) 2. Add one spatula load of copper oxide powder to acid. Keep mixing it until it dissolve. Repeat until no more powder dissolves. (2 spatulas, beaker) 3. Filter the mixture. Filter papers stops unreacted copper oxide which did not react with sulphuric acid and allows dissolved copper sulphate salt to go through. (flask, filter paper, funnel) 4. Heat up the filtrate in the evaporating dish to evaporate water, allowing crystals of copper sulphate to form (Bunsen burner, mat, tripod, gauze, tongues, evaporating dish)

Questions 1. What do we use to filter the mixture? A. Filter Paper 2. Can you name two apparatus we would use to neutralise sulphuric acid. A. Bunsen Burner, Mat, Tripod, Gauze, Tonges, Evaporating Dish