12.6 – How can we use ions in 12.6 – How can we use ions in solutions?solutions?

• Ionic compounds have many uses and can provide other substances.

• Electrolysis is used to produce alkalis and elements such as chlorine and hydrogen.

• Oxidation-reduction reactions do not just involve oxygen.

• Soluble salts can be made from acids and insoluble salts can be made solutions of ions.

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Metal ionsMetal compounds in a solution contain metal ions. For example, consider calcium chloride:

Chlorine is in group 7 so a chloride ion will be Cl-

Calcium is in group 2 and has two electrons in its outer shell, so it will form a Ca2+ ion.

Calcium chloride has the formula CaCl2

Sodium atomSodium atom Chlorine atomChlorine atom

Click Again

Electron transferElectron transfer

+ -

Sodium ChlorideSodium Chloride

Positive and negative ions attract

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ElectrolysisElectrolysis

Molecule of solid copper chloride

CuCl2 (s)

Molecule of solid copper chloride after being dissolved

CuCl2 (aq)chloride

ionCopper

ion

If you melt or dissolve an ionic compound (such If you melt or dissolve an ionic compound (such as NaCl or CuClas NaCl or CuCl22), then the ions become free to ), then the ions become free to move around – and carry electrical current.move around – and carry electrical current.

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ElectrolysisElectrolysisElectrolysis is used to separate a metal from its compound.

= chloride ion

= copper ion

When we electrolysed copper chloride the _____ chloride ions moved to

the ______ electrode and the ______ copper ions moved to the ______

electrode – OPPOSITES ATTRACT!!!

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Purifying CopperPurifying Copper

++++

----

Solution containing copper ions

Impure copper

Cu2+

Cu2+

Cu2+

Pure copper

At the anode:

Cu(s) Cu2+(aq) + 2e-

At the cathode:

Cu2+(aq) + 2e- Cu(s)

19/04/23Electrolysis equationsElectrolysis equationsWe need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride):

2 2

2

At the negative electrode the positive ions GAIN electrons to

become neutral copper ATOMS. The half equation is:

Cu2+ + e- Cu

At the positive electrode the negative ions LOSE electrons to

become neutral chlorine MOLECULES. The half equation is:

Cl- - e- Cl2

Oxidation and Reduction in Oxidation and Reduction in ElectrolysisElectrolysis

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At the negative electrode the

positive ions GAIN electrons – this is called Reduction. The half equation

is:

Cu2+ + 2e- Cu

Oxidation Is Loss, Reduction Is Oxidation Is Loss, Reduction Is GainGain

(of electrons)(of electrons)

O I L R I GO I L R I G

At the positive electrode the

negative ions LOSE electrons –This is called Oxidation.

The half equation is:

2Cl- - 2e- Cl2

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Electrolysis of brineElectrolysis of brine

Positive electrode

Negative electrode

Sodium chloride (brine)

NaCl(aq)

Sodium hydroxide (NaOH(aq)). Used to make soap, paper

and ceramics

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) – used to kill bacteria and to make acids, bleach and plastics

Hydrogen gas (H2) – used to manufacture ammonia and margarine

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Electrolysis - summaryElectrolysis - summary1. When an ionic substance is melted or dissolved in

water, the _____ are free to _______ about in the solution.

2. Passing an ________ __________through these _________ or dissolved ionic substances, breaks them down into __________. This is called ___________.

3. During electrolysis, ___________ charged ions move towards the negative electrode and ___________ charged ions move towards the positive ___________.

Move molten ions electric current elements positivelyelectrolysis electrode negatively

Making Soluble SaltsMaking Soluble SaltsThere are 3 types of reaction that can be used to

make soluble salts. All 3 involve:• An Acid• A metal or metal compound

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METAL + ACID SALT + HYDROGEN

e.g. magnesium + hydrochloric acid magnesium chloride + hydrogen

METAL OXIDE + ACID SALT + WATER

METAL HYDROXIDE (Alkali) + ACID SALT + WATER

Method 3

Method 2

Method 1

Making saltsTo form the name of a salt, you just combine the name of the metal involved, with the salt type associated with the acid. Hydrochloric acid makes chlorides, Sulfuric makes sulfates, Nitric makes nitrates.

Hydrochloric acid

Sulphuric acid Nitric acid

Sodium hydroxide

Sodium chloride + water

Potassium oxide

Potassium sulfate + water

Calcium Calcium nitrate + water

Complete the table as practice

Reactions of metals with acids

When a metal reacts with an acid it gives off hydrogen (which can be “popped” using a lit splint). The other product is a salt.

Copy and complete the following reactions:

1) Calcium + hydrochloric acid

2) Zinc + hydrochloric acid

3) Iron + hydrochloric acid

4) Lithium + sulphuric acid

METAL + ACID SALT + HYDROGEN

e.g. magnesium + hydrochloric acid magnesium chloride + hydrogen

Quiz on acids and alkalis

1) This a pH of less than 7

2) This could kill cells

3) A metal hydroxide (e.g. sodium hydroxide) would be an _____

4) When this reacts with a metal hydrogen is released

5) A metal carbonate (e.g. calcium carbonate) would be an _____

6) This would feel soapy on your skin

7) This could be a corrosive

8) This will turn universal indicator purple

9) This would taste sour

10)This means “a base that can be dissolved”

Acid, alkali or both???

Neutralisation reactionsWhen acids and alkalis react together they will NEUTRALISE each other. Neutralisation is an example of a displacement reaction:

OHNa

Sodium hydroxide

ClH

Hydrochloric acid

The sodium DISPLACES the hydrogen from HCl

ClNa

Sodium chloride

H2O

Water

H ions and OH ionsH ions and OH ions• H ions make acids acidic.• OH ions make alkalis alkaline.• The pH scale measures the

alkalinity or acidity of a solution.

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-

During neutralisation reactions the H ions react with the OH ions to form H2O (water).

-+

H (aq) + OH (aq) → H2O(l)-+

Neutralisation experiment

Sodium hydroxide + hydrochloric acid sodium chloride + water

A ____ was formed during the reaction, and we could have separated this by __________ the solution, allowing the salt to Crystallise. The salt that we formed depended on the acid:

•Hydrochloric acid will make a CHLORIDE

•Nitric acid will make a _________

•Sulphuric acid will make a _________

Words to use – nitrate, neutralised, alkali, sulphate, salt, evaporating

19/04/23Reactions of metal oxides with Reactions of metal oxides with acidacidA metal oxide is a compound containing a metal and oxide. They are

sometimes called BASES. A BASE is simply an insoluble alkali – it neutralises acids, but does not dissolve in water. For example:

Mg O NaNa

O

O

Al

AlO

O

Magnesium oxide Sodium oxide Aluminium oxide

METAL OXIDE + ACID SALT + WATER

Copy and complete the following reactions:

1) Magnesium oxide + hydrochloric acid

2) Calcium oxide + hydrochloric acid

3) Sodium oxide + sulphuric acid

MgO

H Cl

Mg ClCl

HH OH Cl

Using Bases to Make Salts

Because Bases are insoluble the procedure for making a salt is very slightly different…

…Instead of simply evaporating off the water, you have to first remove any remaining (or excess) Base by filtration.

1) Drop the base into the acid…

2) Filter it to remove any leftover base

3) Evaporate it to get the salt

Ammonium SaltsAmmonium Salts• Ammonia (NH3) is a gas that dissolves in water to

make an alkali (Ammonium hydroxide).• This can then be used to make Ammonium salts by

reacting it with an acid.

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Ammonia + Nitric acid Ammonium Nitrate

NH3(g) + HNO3(aq) NH4NO3(aq)

• Notice how NO water is made in this neutralisation reaction.

• Ammonium salts make good fertilisers because plants need nitrogen to make proteins (to grow). Ammonium Nitrate is the best for this purpose – can you see why??

Making Insoluble SaltsMaking Insoluble Salts• Doesn’t usually require an acid.

• Insoluble salts can be made by mixing appropriate solutions of ions (soluble salts), so that a precipitate is formed.

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Precipitation can be used to remove unwanted ions from solutions, for example in treating water for drinking or in treating effluent. – The filter is covered in ions, which form precipitates with ions in the water.

Barium chloride + Sodium sulfate Barium sulfate + Sodium chloride

BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)

An example question on reactivityWhich metal is most reactive?

Metal Reaction with dilute acid

Reaction with water

Reaction with oxygen

ASome reaction Slow reaction Burns brightly

BNo reaction No reaction Reacts slowly

CNo reaction No reaction No reaction

DViolent reaction Slow reaction Burns brightly

EReasonable reaction

Reacts with steam only

Reacts slowly