GCSE Chemistry C2 topic notes

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Salts and Electrolysis Topic Notes

Neutralisation Reaction:

An Acid always contains an H ion

An Alkali always contains an OH ion

A Neutralisation reaction is:

As well as water, a salt is produced in a

Neutralisation Reaction.

Acid +

Metal = Salt + Hydrogen

Acid +

Carbonate = Salt + Water + Carbon Dioxide

Acid +

Metal Oxide = Salt + Water

If Acid is:

HCl = Chloride Salt so the ending is Chloride

H SO = Sulphate Salt so the ending is Sulphate

HNO = Nitrate

Salt so the ending is Nitrate

Soluble salts (salt that can be dissolved) can be made by:

Metals – Some

e.g. Na and K are too reactive, others e.eg. Au are too unreactive

and so can’t be added direct.

Insoluble

Bases – the base is added to the acid until no more will react and

then the excess solid is filtered off. E.g. insoluble base = oxides of

transition metals such as iron oxide( Fe O )

Alkalis – an

indicator is used to show when the acid and alkali have reacted to produce a

salt solution.

Making Insoluble Salts from

Solutions:

Making Soluble Salt (CuSO ):

Insoluble Base + Acid = Soluble Salt and Water

Same for any insoluble Base e.g. MgO

Only practical that you need to know the method

Making insoluble salts:

A precipitate is the formation of an insoluble

salt.

KI + Pb (NO

) = KNO

+ PbI

We filtered the product:

To islolate

the PbI we could have washed and dried

the salt

This gets rid

of any excess KNO .

Practical use for Precipitation:

Remove

pollutant metal ions from the waste water of a factory.

Make an Insoluble

Metal Hydroxide E.g. Pb(OH)

precipitate out.

This forms

a sludge that can be separated from water.

Ammonium Salts:

Nitric Acid + Ammonia Hydroxide = Ammonium Nitrate

Ammonium salts are made in neutralisation reaction

They have a lot of Nitrogen that is needed for

plants to grow

Hence ammonium nitrate is used as a fertiliser

All sodium and nitrates are soluble.

Rates of Reactions Topic Notes

Fast and Slow Reactions:

The Rate of a Reaction is the time it takes for the reactant

to change into the product.

Things that affect the rate of a reaction:

Temperature

Concentration

Surface

Area

Catalyst

Collision Theory:

The effect of certain conditions on the rate of reaction can

be explained by the collision theory between particles.

For two particles to react:

They must

collide

Must have

enough activation energy

Activation Energy

= Minimum Energy needed for a Successful Collision

Temperature:

Particles have more energy so are more collisions. So a

faster rate of reaction.

Heating up

the Chemicals and Particles

Particles are

hotter so have more Energy

Particles

get more Energy and move Faster

Particles

move faster and have more collisions

Faster Rate

of Reaction

Also:

More

particles have the activation energy (minimum energy for an successful

collision)

So more

successful collisions because the particles don’t need as much energy to react

Faster Rate

of Reaction

Concentration/Pressure:

There are more particles so there will be more collisions. So

a faster rate of reaction.

Increasing

the Concentration of the Particles

More

particles in the same Volume of Solution

Greater chance

of particles colliding in the solution and therefore more collisions

Increased

Rate of Reaction

The concentration of a solution tells us how many particles

have been dissolved in a certain volume. The Unit of Concentration is

mol/dm (moles per dm ).

Surface Area:

There are more particles exposed so there will be more

collisions. So a faster rate of reaction.

Split up

the pieces – Increase Surface Area

More area

exposed – Greater Surface Area

More

Surfaces exposed – so more particles can collide

Greater

chance of particles colliding than in a lump of solid

Faster Rate

of Reaction

Catalyst:

Catalyst =

Speeds up the rate of a reaction but remains chemically unchanged at the end of

the reaction

A Catalyst works by offering an alternative pathway of lower

activation energy.

Adding a

Catalyst to Increase the Rate of the Reaction

The

Particles do not need as much Energy to React

Particles

React more easily as more of the particles have enough energy to react.

Catalysts are important for industry:

Products

are made more quickly

Catalysts

can reduce the need for high temperatures

Energy of Reactions Topic Notes

Energy and Reversible Reactions:

Equilibrium: When the reactants are making the products at

the same rate as the product are making the reactants.

Reversible Reactions: Where the reactants make the product

and the products make the reactants.

In a Reversible Reaction one

way is always endothermic and the other is exothermic. It is the same value of

energy taken in and released.

Exothermic Reaction – Transfers

energy to the surroundings. E.g. Combustion, oxidation reactions and

neutralisation.

Endothermic Reaction – Takes

energy from the surroundings. E.g. thermal decomposition

Breaking Bonds = always

endothermic (E.g. Photosynthesis)

Making Bonds = always

exothermic (E.g. Respiration)

Whether a reaction is

endothermic or exothermic overall depends on the energy values for the bond

breaking and making.

If Exothermic Overall: Making

bonds is greater than breaking bonds

If Endothermic Overall:

breaking bonds is greater than making bonds

Electrolysis Topic Notes

Electrolysis means splitting up

using electricity. Using Electricity to break down a substance. An electrolyte

is the substance that is broken down by electrolysis.

OIL RIG:

Gaining electrons is called

Reduction and losing electrons is called Oxidation.

Oxidation Is Loss, Reduction Is Gain

The

Electrolysis of Molten Lead Bromide:

Electricity

is passed through molten lead bromide.

The positively charged ions move to

the negative electrode during electrolysis. They receive electrons and are

reduced. Here molten lead is produced.

Negatively charged ions move to the

positive electrode during electrolysis. They lose electrons and are oxidised.

Bromine gas is produced.

Lead Bromide -> Lead + Bromine

Electrolysis of CuCl :

The

negative (chloride) ions go to the Positive electrode, lose electrons and form

Chlorine gas.

The

positive (copper) ions go to the Negative electrode, gain electrons and form

Copper.

Copper is

formed at the negative electrode and Chlorine gas is formed at the positive

electrode.

You can

test for Chlorine gas because it will turn litmus paper red because it’s

acidic.

Aluminium:

Aluminium is a reactive metal that has a low density but is

strong. Aluminium ore is a bauxite

Aluminium Bauxite is mixed with Cryolite to lower the melting

point from 2500 → 850℃ It has to be molten

for the ions to move.

The high temperatures mean

that a lot of energy is required so the plant will have its own power station.

Extraction of Aluminium:

Negative Electrode –

Positive Al atoms are attracted to the negative electrode. They gain electrons

and are reduced to form aluminium (atoms).

Positive Electrode –

Negative O ions are attracted to the

positive electrode. They lose electrons and are oxidised to form Oxygen. This

reacts with the carbon electrode to form Carbon dioxide.

Electrolysis

of Brine:

Molten NaCl produces Na

+ Cl ions

NaCl solution (brine) produces Na + Cl + H +

OH

When we electrolyse brine, the products depend on their

reactivity.

The more

reactive ions stay in the solution. Na + OH →NaOH (alkaline turns universal

indicator blue/ red litmus blue)

+ve

electrode 2Cl -2e → Cl

–ve

electrode 2H + 2e → H

Uses:

Chlorine = Disinfectant in swimming pool

Hydrogen = Rocket Fuel

Sodium Hydroxide = bleach

What happens in the electrolysis of Brine?

NaCl(aq) → Na + Cl + H +

OH

Positive Electrode:

The

negative chloride ions are attracted to the positive electrode (anode).

They lose

electrons

It Oxidises

to form Chlorine Gas (molecules)

2Cl (aq) –

2e → Cl (g)

Negative electrode:

The

positive Sodium ions are attracted to the negative electrode (cathode).

They gain

electrons

It reduces

to form Sodium (atoms).

Na + e → Na(s)

An electrolyte is a substance that is broken down by

electrolysis.

Test for Chlorine:

Red litmus paper → blue

Test for Hydrogen:

The pop test. Lit splint → pop

Electroplating:

At the

negative electrode – Copper ions gain electrons (reduction) to form Copper

metal. Cu + 2e → Cu

At the

positive electrode – Copper strip loses electrons (oxidisation) to form Copper

ions. The positive electrode dissolves Cu

– 2e → Cu

Electroplating is useful because we can plate items to make

them look nicer and its cheaper than using pure metal.

Copper plating:

Negative Electrode – Copper goes to the Negative

electrode because they are positive ions. They gain 2 electrons and are

reduced. This makes a layer of Copper on the nail. Cu + 2e → Cu

Positive Electrode – Sulphate stays in solution. (The

solution is losing copper ions and it wants them back. This is because the

positive electrode is being dissolved). The copper atoms at the copper

electrode lose electrons, they are oxidised. This forms copper ions which go

back into the solution. Cu – 2e → Cu

The concentration of the solution stays the same because the

copper is lost at the same time it is gained. It is losing/ gaining electrons

at a steady rate.

Structure and Bonding Topic Notes

Atomic

Structure:

Mass number is the number of protons and neutrons. It is all

the mass in the Nucleus.

Atomic number is the number of protons. For an atom only,

this is the same as electrons.

Protons: atomic number

Electrons: Atomic number

Neutrons: Mass number – atomic number

Electrons:

The number of electrons in the outer shell tells us the group

number for that element.

Isotopes:

Almost all elements have isotopes.

E.g. Carbon C p=6 n=

6 e = 6

Carbon has two other isotopes:

C 13

C 14

Protons

6

6

Neutrons

7

8

Electrons

6

6

Table to show the differences between isotopes:

Same

Different

Proton

Number

Neutron

Number

Electron

Number

Mass Number

Atomic

number

Unstable

Charge of

the atom

Physical

properties

Chemical

Properties

Carbon Dating:

The trees and plants take in Carbon 12 +14 through

photosynthesis.

Humans and animals take in the carbon when eating the

plants.

They die and the carbon levels no longer increase. C12

stays constant, however C14 decays, giving out radiation.

They measure the ratio between C14 and C12 levels to

identify the age of the object.

Every time it decays there is half as much carbon.

This is a half life.

Ionic Bonding:

Between a metal and a non-metal

To gain a full outer shell

Involves the loss and gain of electrons to form ions.

It is not and actual bond but is:

A strong

electrostatic attraction

Between all

oppositely charged ions in a giant lattice

Properties:

High

melting point – need a lot of energy to break the electrostatic attraction.

High

boiling point

Only

conducts when molten or in a solution – because the ions are free to move and

carry the charge

Lithium loses and electron to gain a full outer shell.

Lithium becomes a +1 ion.

Fluorine gains an electron to gain a full outer shell.

Fluorine becomes a -1 ion.

Covalent Bonding:

Between two non-metals

Involves the sharing of electrons

A Covalent Bond is a shared pair of e (electrons)

Covalent Compounds form 2 types of molecules:

Simple

Molecular

E.g. HCl, H O, CH , NH

Simple molecules have low boiling/ melting points

because:

The weak

intermolecular forces are broken. Not the strong covalent bonds.

Not much

energy is required.

Giant

Covalent

Only examples you need to know are diamond (C),

graphite (C), silicon dioxide (SiO )

These structures only have strong covalent bonds.

Diamond:

Diamond

has a very high melting/ boiling point

Graphite:

It has a delocalised e between the layers of Carbon atoms. This

means:

It can

conduct electricity

The layers

can be separated because it is soft

Fullerenes are used as lubricants

because the layers slide past each other with no covalent bonds formed.

SAlts and electrolysis

Rates of reactions

Energy of reactions

Electrolysis

Structure and bonding