What is an alkali?
Alkalis are bases that dissolve in water to make alkaline solutions.
What is a base?
Bases are substances that will neutralise acids.
Which ions are produced by alkalis when dissolved in water?
Hydroxide ions, OH-(aq).
What pH are acids?
Less than pH7.
What pH are alkalis?
More than pH7.
What is a neutralisation reaction?
When an acid reacts with a base to produce a salt and water. Acid + metal ➡️ A salt + hydrogen.
Which ions are produced by acids when they are added to water?
Hydrogen ions, H+(aq).
Describe the method of making soluble salts from solutions (neutralisation reaction).
1. Measure out acid and gently warm using bunsen burner for 1 minute max.
2. Add base one spatula at a time until it no longer dissolves (reacts).
3. Filter mixture into evaporating basin to remove unreactive base.
4. Heat basin with bunsen burner or leave to evaporate the water.
Describe the method of making soluble salts from solution using an indicator.
1. Measure out acid and add universal indicator.
2. Add base drop by drop until universal indicator turns green (neutral).
3. Add spatula of activated charcoal and stir until solution is clear.
4. Filter solution and evaporate.
Describe the method for making insoluble salts from solution (precipitation reaction).
1. Add a soluble salt to another soluble salt.
2. Filter to remove insoluble salt produced.
3. Evaporate to get soluble salt.
During electrolysis of sodium chloride solution, one product is hydrogen.
How does a hydrogen ion change into a hydrogen atom?
They gain 1 electron.
Suggest why a mixture of sulfuric acid might be heated into a solution.
To increase rate of reaction.
Ammonia dissolves in water to produce an alkaline solution. Which ion makes ammonia solution alkaline?
Ammonia= Nitrogen and Hydrogen
When sodium chloride solution is electrolysed, one product is chlorine.
Name two other products from the electrolysis of sodium chloride solution (2 marks).
Sodium Hydroxide (1).
What is electrolysis?
Electrolysis is the process that uses electricity to break down ionic compounds into elements.
Why can ionic compounds only be electrolysed when molten or dissolved in water?
Only when the compounds are molten or dissolved because then their ions are free to move to the electrodes.
What are electrodes often made out of?
An inert substance that will not react with the products.
Sometimes, such as in electrolysis of Aluminium Oxide, graphite (carbon) electrodes are used.
In electrolysis, where do the positive ions go and where do the negative?
Positive ions go to the negative electrode and gain electrons, so are reduced.
Negative ions go to the positive electrode and lose electrons, so are oxidised.
What does 'OIL RIG' stand for?
Oxidation Is Lost, Reduction Is Gain.
What are halogens?
Group 7 elements, which always pair up.
Complete the half equation for the formation of chlorine at the positive electrode: 2Cl-➝
2Cl- ➝ Cl2 + 2e-.
What ions does water contain?
Hydrogen ions and hydroxide ions.
When solutions of ions in water are electrolysed, what is produced at the negative electrode?
Why is aluminium oxide mixed with cryolite before being molten and electrolysed?
Cryolite is added to lower the melting point of aluminium oxide so less energy is needed to melt it.
Aluminium is 3+ and Oxygen is 2-.
What are the half equations for the electrolysis of aluminium oxide?
Cathode: Al3+ + 3e- ➝Al.
Anode: 2O2- ➝O2 + 4e-.
Carbon electrodes are used in the electrolysis of aluminium oxide.
What does this mean?
Oxygen atoms pair to make O2.
O2 reacts with the carbon electrode to make carbon dioxide.
The carbon electrode therefore gets used up so must be replaced.
What is the positive electrode called?
What is the negative electrode called?
What is brine?
Brine is a solution of sodium chloride in water.
What ions does brine contain?
Sodium ions (Na+), Chloride ions (Cl-), Hydrogen ions (H+) and Hydroxide ions (OH-).