C2 Salts And Electrolysis

Question 0

Give example of exothermic reactions.

Answer 0

Combustion, the burning of fuels is exothermic.
Neutralisation reactions(acid + alkali)
Oxidisation reactions. Adding sodium to water produced heat so it is exothermic.
Respiration.

Question 1

Define exothermic reaction.

Answer 1

It is a reaction which transfers energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature.

Question 2

What are the uses of exothermic reactions?

Answer 2

Some hand warmers, use the oxidation if iron in air to produce heat.
Iron turns into hydrated iron oxide. The reaction is similar to rusting. Sodium chloride is used as a catalyst.
Self heating cans of coffee rely on them. Calcium oxide and water react to produce calcium hydroxide.

Question 3

Define endothermic reaction.

Answer 3

An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat and is usually shown by a fall in temperature.

Question 4

What are the uses of endothermic reactions?

Answer 4

They can be used in sports injury packs. They take in heat and pack becomes cold.

Question 5

Give an example of an endothermic reaction.

Answer 5

Thermal decomposition reactions are endothermic.

Calcium carbonate thermally decomposes into CO2 and calcium oxide.

Question 6

Give an example of a reversible reaction and its endothermic/ exothermic properties.

Answer 6

Hydrates copper sulphate thermal decomposes into anhydrous copper sulphate and water. These products produce heat when reacted together.
In a reversible reaction, the forwards energy is the same as the reverse energy.

Question 7

What is a base?

Answer 7

A substance with a pH of greater than 7.

Question 8

What is an alkali?

Answer 8

A soluble hydroxide It forms OH- ions in water.

Question 9

What happens in a neutralisation reaction?

Answer 9

Acid + base = salt + water.

Question 10

What are the state symbols?

Answer 10

S- solid l- liquid. g-gas. aq-dissolved in water

Question 11

What happens when an acid reacts with a metal.

Answer 11

Acid + metal = salt + hydrogen.

Question 12

What happens when copper is mixed with a dilute acid?

Answer 12

Nothing will happen. As copper is less reactive than hydrogen no hydration or salt will be produced.

Question 13

What salts will hydrochloric acid produce when reacted with metal?

Answer 13

Chloride salts.

Hydrochloric acid+ magnesium = magnesium chloride + hydrogen.

Question 14

What salts will sulphuric acid produce when reacted with metal?

Answer 14

It will always produce sulfate salts.

Sulfuric acid+ magnesium = magnesium sulphate + hydrogen.

Question 15

What are metal oxides and metal hydroxides?

Answer 15

They are bases. Some of them are alkali.

This means they will always react with an acid to produce to salt and water.

Question 16

What happens when ammonia is reacted with nitric acid?

Answer 16

Ammonium nitrate salt will be made but no water.
NH”3” + HNO”3” = NH”4”NO”3”
This is a good fertiliser.

Question 17

How can a soluble salt be made with an insoluble base?

Answer 17

An acid plus a metal a metal hydroxide or oxide(insoluble bases)
If you want to make copper chloride mix copper oxide and hydrochloric acid.
Add the metal oxide or hydroxide or the acid. (It will be in powder form)
This will dissolve. Keeping adding it till nothing else dissolves.
Filter out the excess metal.
Evaporate off the water to get the salt.

Question 18

How can a soluble salt be made using an alkali and acid?

Answer 18

First you react some acid and alkali them with an indicator. Measure out the amounts and stop when the indicator tells you it is neutral.
then do it again with out the indicator so the salt with have the right colour.
Evaporate the water away.

Question 19

How is an insoluble salt made?

Answer 19

A precipitation reaction must take place.
Insoluble salts can sometimes be made by combining two solutions containing soluble salts.
Each solution containing one of the ions of the in soluble salt.
Filter the salt out, wash it with distilled water and leave it to dry.

Question 20

What happens when an electric current goes through something ionic?

Answer 20

It has to be molten or in a solution but it will be broken down. This is called electrolysis.

Question 21

What is an electrolyte?

Answer 21

The liquid that conducts electricity in electrolysis.

They must contain free ions. They’re usually the molten or dissolved ionic substance.

Question 22

Explain the movement of electrons in electrolysis.

Answer 22

Electrons are taken away from ions in the anode and given to the ions in the cathode.

Question 23

What is oxidation and reduction?

Answer 23

Oxidation is the loss of electrons and reduction is the gain of electrons. These two always happen in electrolysis.

Question 24

Explain the electrolysis of lead bromide.

Answer 24

It is heated to produce molten lead bromide.
At the cathode, 2 plus lead ions are attracted and will gain two electrons meaning they become full atoms in reduction.
At the anode, 1- bromine ions are attracted and they lose electrons becoming full atoms. This is oxidation. Bromine is created here.

Question 25

If there are metal ions and hydrogen+ ions at the negative electrode, what will happen?

Answer 25

The metal ions will stay in the solution if the metal is more reactive than hydrogen. This is because the more reactive the element, the more eager it is to stay as an ion. As long as the metal is more reactive, hydrogen will be created.

Question 26

If there are OH- and halide ions at the positive electrode, what will happen?

Answer 26

Molecules of the halide will form. If there is no halide there, oxygen will always form.

Question 27

Explain the electrolysis of sodium chloride.

Answer 27

It will be dissolved in water.
Hydrogen, chlorine and sodium hydroxide (NaOH)will be produced.
At the cathode, two hydrogen ions will accept two electrons and become one molecule of hydrogen gas. Sodium won’t be produced here as it is more reactive than hydrogen.
At the anode, two chloride ions will lose their electrons and become one molecule of chlorine gas.
Sodium and hydroxide ions will be left in the solution and they will form sodium hydroxide.

Question 28

What are useful products that can be made from the electrolysis of sodium chloride solution?

Answer 28

The chlorine can be used in the production of bleach and plastics.
The hydrogen can be used to make margarine.
Sodium hydroxide is a strong alkali and it is used in the chemical industry e.g. to make soap.

Question 29

What happens before electrolysis in the process of extracting aluminium from its ore?

Answer 29

It’s main ore is bauxite and after mining and purifying it, a white powder is left.
This is pure aluminium oxide. Al”2”O”3”
This is then electrolysed.

Question 30

What happen in the electrolysis in the process of extracting aluminium from its ore?

Answer 30

Aluminium oxide has a melting point of 2000C which would cost a lot.
Instead the oxide is dissolved in molten cryolite (a less common ore of aluminium) this brings the temperature down to 900C which makes it cheaper.
The electrodes are made of granite. A good electricity conductor.
Aluminium forms at they cathode and oxygen at the anode. This will react with carbon in the electrode to produce CO2. This means the anode will have to be replaced every now and again as it gets used up.

Question 31

What is electroplating?

Answer 31

Using electrolysis to coat the surface of one metal with another.

Question 32

How does electroplating work?

Answer 32

The cathode is the metal to be plated and the anode is the pure metal to act as the plate. The electrolyte also contains ions of the plating metal.

Question 33

What is the purpose of electroplating ?

Answer 33

Decoration. Silver looks nice and it is cheaper to make a cup out of brass and plate it but it still looks nice.
Conduction. Metals like copper conduct electricity well. This means they can be plated on electronic circuits for computers.
To protect a metal from corrosion.

Question 34

Why aren’t very reactive metals added to acid?

Answer 34

Because the reaction would be too violent and everything would be killed.

Question 35

How can a salt be made with an acid and a metal.

Answer 35

Add the two together. The metal will have to be more reactive than hydrogen but not too reactive or it will be too violent. Hydrogen will also be produced.

Question 36

Most chlorides, sulphates and nitrates are …

Answer 36

Soluble in water.

Question 37

Most oxides and hydroxides are…

Answer 37

Insoluble in water.

Question 38

What is the general way of making salts?

Answer 38

Replace the hydrogen in an acid with a metal.

Question 39

What is a precitate

Answer 39

An insoluble thing.

Question 40

Give an example of making a salt with an acid and a metal oxide.
Give the equation.

Answer 40

CuO + H”2”SO”4” = CuSO”4” + H”2”O

Question 41

How is a soluble salt made with an acid and metal.

Answer 41

Measure out acid and put it in a beaker.
Add metal untill it stops reacting. It should dissolve and fizz.
When this stops filter out the unwanted metal and evaporate out the water to get your salt.

Question 42

How can a soluble salt get made?

Answer 42

Acid + metal.
Acid + alkali.
Acid + metal oxide.