C3 Chemical Changes
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What is an acid?
A substance that produces H+ ions
What is a base?
A substance that neutralises an acid
What is an alkali?
A substance that produces OH- ions
What is a strong acid?
An acid that almost completely ionises in water
What is a weak acid?
An acid that does not fully ionise in water
What is a concentrated acid?
An acid that has a large number of acid molecules compared to water
What is a dilute acid?
An acid that has a low number of acid molecules compared to water
What happens if you increase the H+ concentration by a factor of 10?
The pH decreases by 1
What is the reaction between a metal and an acid?
Acid + Metal —-> Salt + Hydrogen
What is the reaction between a metal oxide and an acid?
Acid + Metal Oxide —> Salt + Water
What is the reaction between a metal hydroxide and an acid?
Acid + Metal hydroxide —> Salt + Water
What is the reaction between a metal carbonate and an acid?
Acid + Metal Carbonate —> Salt + Water + Carbon dioxide
What is the test for hydrogen?
Take a lighted splint which makes a “squeaky pop” sound
What is the test for carbon dioxide?
Bubble through limewater. If present, it turns cloudy
How do you make an insoluble salt?
Precipitation reaction (two soluble salts)
How do you make a soluble salt?
• Acid + insoluble base • Titration (acid + alkali)
What is the method for a precipitation reaction?
• Add a spatula of each soluble salt to a test tube with deionised water • Mix both test tubes together and mix together, creating an insoluble precipitate • Filter the mixture • Rinse the contents with deionised water • Leave to dry in an oven
What is the method for an acid + insoluble base?
• Heat the acid to speed up the reaction • Add the base to the acid until it is in excess • Filter off the mixture, leaving you with the salt and water • Gently heat to evaporate the water • Leave to cool and crystallise
What is an electrolyte?
A molten or dissolved ionic compound that can conduct electricity
What happens during electrolysis?
• The cations move towards the cathode and become reduced • The anions move towards the anode and become oxidised
Why can an ionic compound not conduct electricity?
The ions are in fixed positions and cannot move
What happens at the cathode in the electrolysis of aqueous solutions?
If the metal is more reactive than hydrogen, hydrogen is produced
What happens at the anode in the electrolysis of aqueous solutions?
If none of the halide ions (chlorine, bromine and iodine) are present, oxygen is formed
What is the half equation if oxygen is produced at the anode in electrolysis of an aqueous solution?
4OH- —-> O2 + 2H2o + 4e-