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GCSE Chemistry (C2) > Salts and Electrolysis > Flashcards

Salts and Electrolysis Flashcards

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1
Q

What is an acid?

A

Substances with a pH less than 7

They are proton donors, so produce H+ ions when added to water

They are the chemical opposite of an alkali

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2
Q

What is a base?

A

Proton acceptors with a pH value above 7

They will react with acids to neutralise them and produce salt as one of the products

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3
Q

What is an alkali?

A

Bases that dissolve in water

They have a pH value greater than 7

They produce OH- ions when in solution

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4
Q

Which metals in the reactivity series will acids react with?

A

Those above hydrogen

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5
Q

Why wouldn’t you react sodium or potassium with an acid in a lab?

A

Because the reaction is too violent to be done safely

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6
Q

What is the reaction that occurs when metals react with acids?

A

Metal + Acid → Salt + Hydrogen

MASH

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7
Q

What is produced in a neutralisation reaction?

A

Acid + Alkali/Base → Salt + Water

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8
Q

How can salt be made from a metal or base that is insoluble in water?

A
  • It is added a little bit at a time to the acid until the acid has reacted
  • The mixture is then filtered to remove the excess solid reaction
  • This leaves a solution of the salt
  • The solid salt is made when water is evaporated from the solution so that is crystallises
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9
Q

How can salts be crystallised from solutions?

A

By evaporating off water

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10
Q

How can we make soltuble salt?

A

By reacting an acid with an alkali

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11
Q

What compound is produced in every neutralisation reaction?

A

Water

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12
Q

Why do we need to use an indicator to show what neutralisation is complete?

A

Because there is no visible change

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13
Q

What is ammonia solution?

A

An alkali that does not contain a metal

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14
Q

What is the chemical formula for ammonium nitrate?

A

NH4NO3

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15
Q

What are ammonium salts used for?

A

As fertilisers

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16
Q

How can insoluble salts be made?

A
  • By mixing solutions of soluble salts that contain the ions needed
  • This forms a precipitate
  • The precipitate can then be filtered from the solution, washed with distilled water, and dried
17
Q

Give a useful application of precipitation

A

It can be used to remove some pollutants, such as metal ions, from water.

The water is treated by adding substances that react with the pollutant metal ions dissolved in the warer to form insoluble salts

18
Q

What is electrolysis?

A

A process that uses electricity to break down ionic compounds into elements

19
Q

What must happen to ionic compounds before they can be electrolysed and why?

A

They must be molten or in a solution so that their ions are free to move to the electrodes

20
Q

What is an electrolyte?

A

A substance containing free-moving ions that is broken down by electrolysis

21
Q

Describe what happens during electrolysis/how it works

A
  • The electrical circuit has two electrodes that make contact with the electrolyte.
  • The ions in the electrolyte move to the electrodes where they are discharged to produce elements
  • Positively charged ions are attracted to the negative electrode, where they are reduced to form either metals or hydrogen
  • Negatively charged ions are attracted to the positive electrode where they are oxidised to form non-metallic elements
22
Q

What is reduction and oxidation?

A

Reduction is losing electrons (positive ions)

Oxidation is gaining electrons (negative ions)

Oxidation Is Loss

Reduction Is Gain

(OIL RIG)

23
Q

Write out the haf equation for the oxiation of lead at the negative electrode

A

Pb2+ + 2e- → Pb

24
Q

Complete the half equation for the reduction of bromine at the positive electrode

A

2Br → Br2 + 2e-

25
Q

When aqueous solutions are electrolysed, what is produced at the positive electrode?

A

Oxygen gas is always produced unless the solution contains halide ions, in which case the halogen will be produced

26
Q

When aqueous solutions are electrolysed, what is produced at the negative electrode?

A

Hydrogen gas is always produced unless the solution contains ions of a metal that is less reactive than hydrogen

27
Q

What is aluminium oxide mixed with before it is electrolysed and why?

A

Cryolite

This lowers its melting point from 2000°C to 850°C

This means less energy is used

28
Q

What is produced by the electrolysis of aluminium?

A

Aluminium and oxygen

29
Q

What are the positive electrodes used in the electrolysis of aluminium made of and why does this cause problems?

A

Carbon

At the high temperatures at which the reaction takes place, the oxygen reacts with the carbon to produce CO2

This means that the electrodes gradually burn away and have to be replaced

30
Q

What is brine?

A

A solultion of sodium chloride (salt) in water

31
Q

What is produced during the electrolysis of brine?

A

Hydrogen at the negaive electrode

Chlorine at the positive electrode

Sodium hydroxide solution is left behind

32
Q

Why is hydrogen produced when sodium chloride is electrolysed?

A

Because the solution contains hydrogen ions which are discharged in preference to the sodium ions as sodium is more reactive than hydrogen

33
Q

What is the sodium hydroxide produced from the electrolysis of brine used for?

A
  • Making soap
  • Making paper
  • Making bleach
  • Neutralising acid
  • Controlling pH
34
Q

What is the chlorine produced from the electrolysis of brine used for?

A
  • To kill bacteria in drinking water and swimming pools
  • To make bleach
  • To make disinfectant
  • To make plastics
35
Q

What is the hydrogen produced from the electrolysis of brine used for?

A
  • To make margerine
  • To make hydrochloric acid
36
Q

Why might electroplating be done?

A
  • To make an object look more attractive
  • To protect a metal object from corroding
  • To increase the hardness of a surface
  • To reduce costs by using a thin layer of metal instead of pure metal
37
Q

What is electroplating?

A

Using electrolysis to put a thin coating of metal onto an object

38
Q

How is electroplating done?

A
  • The object to be plated is used as the negative electrode
  • The positive electrode is made from the plating metal
  • The electrolyte is a solution containing ions of the plating metal
  • At the positive electrode, ions of the plating metal lose electrons to form metal ions which go into the solution
  • At the negative electrode, metal ions from the solution gain electrons to form metal atoms which are depositied on the object to be plated

GCSE Chemistry (C2) (5 decks)

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