C2 - Salts & Electrolysis
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What is an alkali?
• A soluble hydroxide. - Produce OH- ions when added to water.
What are acids?
Substances that produce H+ ions when added to water.
What are bases?
Substances which neutralise acids.
How is acidity measured?
Using a universal indicator with a pH scale.
What are soluble hydroxides?
Alkali
What are metal oxides and hydroxides?
Bases
What pH is pure water?
7 ie. neutral
What colour does universal indicator turn for acidic substances?
Red
What colour does universal indicator turn for alkali substances?
Purple
What is produced when an acid and metal react?
A salt and hydrogen gas
What is produced when an acid reacts with a base?
A salt and water
What type of reaction occurs between acids and bases?
Neutralisation
What is the equation of neutralisation in terms of ions?
H+(aq) + OH-(aq) —-> H2O(l)
What is a precipitation reaction?
Combining two solutions that contain different soluble salts which react to make an insoluble salt.
How are precipitate reactions used in water treatment?
Raising the pH makes insoluble metal hydroxides precipitate out.
What is electrolysis?
Breaking down a substance using electricity.
What types of substances can be electrolysed?
Ionic compounds can be electrolysed when they are molten or in solution.
What is made from electrolysis?
Positive ions move to the cathode while negative ions move to the anode.
What is the electrolyte?
The substance being broken down.
What are electrodes made of?
Inert substances such as graphite or platinum.
Why are electrodes made of un reactive materials?
So the electrodes don’t react with the electrolyte or the products of electrolysis.
What happens to the ions in electrolysis?
Negative ions are oxidised. Positive ions are reduced.
How does water affect the products of electrolysis?
• The less reactive element between hydrogen and the metal is produced at the cathode. • At the anode, oxygen is often produced from the discharged hydroxide ions.
What is reduction?
Gaining electrons