Which statement is correct?The film is scientifically right, saltwater can conduct so the shark would be electrocuted ORHollywood is incorrect saltwater does not conduct electricity

Your task is to test this claim Your task is to test this claim made by Hollywood. Does made by Hollywood. Does saltwater conduct?saltwater conduct? You will also need to

work out if anything is formed at the electrodes and if so what.

HINT in salty water you have hydrogen, oxygen, sodium and chlorine ions.

The effect of waterThe effect of water

When substances are dissolved in water it is more difficult to predict what is formed as water also forms ions.

The rule is that the less reactive element is usually formed

e.g. if a potassium compound is electrolysed:Cathode -

K+

K+

K+

H+

H+

H+

Electrolysis of brineElectrolysis of brine

Positive electrode

Negative electrode

Sodium chloride (salt) is made of an alkali metal and a halogen. When it’s dissolved we call the solution “brine”, and we can electrolyse it to produce 3 things…

Chlorine gas (Cl2) Hydrogen gas (H2)

Can you write half equations for this?

Can you write equations to show what happens at the electrodes?

Useful products from the Useful products from the electrolysis of brineelectrolysis of brine

Chlorine - bleach

- killing bacteria in swimming pools

- PVC and textiles

Hydrogen - making margarine from vegetable oil

- hydrochloric acid for food and pharmacy

- haber process making ammonia

Sodium Hydroxide - soap

- making paper

- controlling pH

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Electrolysis of NaCl solution

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The positive electrode

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The negative electrode

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Uses of Cl2, H2 and NaOH

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Why is sodium not formed?

In the electrolysis of sodium chloride solution, the Na+ ions might be expected to form sodium at the negative electrode. Instead, hydrogen gas is produced here.

For all ionic compounds containing a metal that is more reactive than hydrogen, electrolysis of a solution of the compound will produce hydrogen rather than the metal.

At the negative electrode, H+ ions compete with Na+ ions. The H+ ions gain electrons; the Na+ ions stay in solution.

This is because sodium chloride solution also contains H+ ions from some of the water: H2O (l) H+ (aq) + OH- (aq).

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How does sodium hydroxide form?

Sodium chloride solution has four types of ions:

What is the overall equation for the electrolysis of brine?

The Cl- ions form chlorine at the positive electrode and the H+ ions form hydrogen at the negative electrode.

Na+ and OH- ions are left behind, and so a solution of sodium hydroxide (NaOH) is formed.

Na+ and Cl- ions from the sodium chloride

H+ and OH- ions from the water.

2NaCl (aq) + 2H2O (l) H2 (g) + Cl2 (g) + 2NaOH (aq)

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Fill in the gaps

What is the industrial importance of electrolysis of brine? (4 marks)