Review of Chemistry

8/11/2019 Review of Chemistry

1/34

Chemistry Revision


2/34

AtomsAll chemical elements are made up of atoms

Every atom is made up of smaller particles; neutronsandprotonsin the atoms nucleus which is

surrounded by electrons

Atoms become ions when they gain/lose an electron

The atomic numberis the number of protons in the

nucleus ( which is the same as the number of

electrons)The mass number is the protons + neutrons in the

nucleus, the mass of an electron is so small it is

considered to be negligible


3/34

Atom Mass

A is the relative atomic mass

M is the relative molecular mass,

For example- HO has a relative

molecular mass of 18 [(2x1) + 16)

For ionic compounds the term relativeformula mass is used as there is no

separate molecules

r

r


4/34

Isotopes

Isotopes are different forms of the same

element

If an isotope has more neutrons than protons,

it can sometimes be unstable and is likely to

decay


5/34

Alkali MetalsGroup 1 in the periodic table

More reactive as you go down the group

Low densities

Ionic compounds +1 charge

Alkaline solution

Soft shiny metals

React with the oxygen in the air and become tarnishedso they

are stored in oil

React vigorously with water, they fizz and produce hydrogen gasIdentifying Alkali Metals- identified using the flame test

Lithium burns with a red colour

Sodium burns with a yellow/orange colour

Potassium burns with a lilac/purple colour


6/34

HalogensGroup 7 in the periodic table

More reactive as you go up the group

Reacts with alkali metals

Halogens react with iron- iron wool bursts into flames when

it reacts with fluorine gasHalogen displacement reactions mean the more reactive

halogen displaces the less reactive halogen

Identifying Halides- identified using the precipitation test

using silver nitrate

Chlorine- white/silver

Bromine- Pale yellow/cream

Iodine- yellow


7/34

MetalPhysical PropertiesThe following properties applies to copper

High electrical conductivity

High thermal conductivity

High melting point and boiling point

DuctileCorrosion resistant

Antibacterial

Malleable (can be hammered/squashed into differentshapes)

Easy to alloy


8/34

Metallic Structure

positive

The structure can

easily pass the

vibration of hot

particles along andthe free electrons

move faster which

is why metals aresuch good

conductors


9/34

Ionic Compound- Physical Properties

The following properties applies to Sodium Chloride

High melting point- because they have strong attractiveforces ( lot of energy to separate)

Solid sodium chloride does not conduct electricitybecause the lattice holds to sodium and chloride ions infixed positions ( Not free to move)

but it can conduct electricity does if dissolved in water

as the lattice breaks down so the ions move freelyBrittle- if a stress is applied will make the layers move

Soluble in water


10/34

Ionic Structure

The sodium lost an electron andthe chlorine gained an electron


11/34

Simple Covalent Molecule- Physical properties

Low melting point( strong bonds

but weak attractive forces)

Liquid at room temperature

Poor conductor of electricity

Water soluble


12/34

Simple Covalent Structure

A covalent bond

happens when

electrons are

shared betweento atoms


13/34

Giant Covalent SubstanceDiamond

Transparent + crystalline (used for jewellery)

Extremely hard ( lot of energy needed to breakdown lattice)

Electrical insulator

High melting point

Graphite

Grey/black shiny solid

Very soft- used in pencils

Conducts electricity( along the layer aselectrons are free to move but does notconduct across the layers)High melting point

Slippery( hexagonal layers slide across eachother

Both different forms of carbon


14/34

Structure of diamond and graphite

Carbon atoms each connected to

4 other atoms

3-d Lattice based on a tetrahedral

unit cell

graphite Diamond

Made up of layers

Arranged in hexagonal ringsEach carbon atom is connected

to 3 other atoms

Bonds between layers are weak

Layers can slide over each other


15/34

Carbon Nanotubes

One of the stiffest and strongest fibres knownHigh electrical conductivity

Formed when graphite layers are rolled up intotubes

Covalently bonded hexagonal carbon sheetsmake it very strong

Proposed uses for electrical connections insmaller circuits

Used in bike components, boat hulls andbonding of things like wind-turbines

Could be used for cancer treatment


16/34

Smart MaterialsSmart materials are materials that change when there is a change

in their surroundingsThermochromic PigmentsSpecial paints which change

colour when there is a change in

temperature

Most are base on liquid crystal

technology

Used in mugs to see hot

temperatures

Also used in T-shirts

Photochromic PigmentsContain organic molecules which will

change colour when exposed to light,

especially ultraviolet light

Used in T-shirts and glasses


17/34

Smart Materials

Shape-memory

polymersPlastics that regain their

shape when heated

Somewhere betweenthermoplastics and

thermosets

Used for sealing around

window framesCould be used for car

bodies (fix the dent)

or stitches which will adjust

to tension

Shape-memory alloysMetal alloys that regain

their shape when heated

Used for spectacle frames,

surgical plates and wires

HydrogelsPolymers that absorb or

expel water and swell or

shrink the size itswells/shrinks to depends

on changes in PH or

temperature

Used in artificial muscles


18/34

Rates of reaction

We can measure the rate of reaction by :

-Capturing & measuring the volume of gas

produced by a reaction

- Measuring the change in mass

- Measuring the amount of light passing

through a reaction that is producing a

precipitate


19/34

Chemical Reactions

Chemical reactions occur when molecules/atoms/ionscollide but it only happens there is enough energy forthe bonds to break and be reformed.

Successful collisions per second = collision frequency

Factors that affect the rate of reaction

1. Temperature

2. Surface Area

3. Concentration

4. Use of a catalyst


20/34

Catalysts

These aresubstances that

increase the rate of

reaction but remain

chemicallyunchanged

It reduces the

amount of energyneeded which will

increase the

collision frequency

Used in the production of

bulk materials eg. Sulphuric

acid and food processing


21/34

Percentage Composition of Compounds

Calculate the % of copper in copper sulphate,CuSO4 Relative atomic masses: Cu = 64, S = 32and O = 16

relative formula mass = 64 + 32 + 4x16 = 160

only one copper atom of relative atomic mass 64

% Cu = 64 x 100 / 160 = 40% copper by mass inthe compound

Example


22/34

Masses of reactants and products

The total mass of the reactants equals the totalmass of the products


23/34

The Yield of a Chemical reaction

Yield= What was obtainedWhat was expected

X 100 %

Example: Mass of carbon monoxide you would expect to reduce 1000g of iron oxide

FeO + 3CO 2Fe + 3CO

FeO CO

Mass(g) 1000 ? = 525

Mr 160 40

Mass/Mr 6.25 18.75 (3x6.25)

1 : 3


24/34

Combustion of methane

The breaking of the bong is endothermic (gives

out heat

The formation of the bond is exothermic (takesin heat)


25/34

Oil

Crude oil is a mixture ofhydrocarbons

Fractional distillation is

how you separatedifferent fractions of oil

The larger the molecule

the higher the boilingpoint


26/34

Alkanes and Alkenes

Alkanes are saturated hydrocarbons which

means they only contain single bonds

Alkenes are unsaturated hydrocarbons they

have a double bond

Alkenes can be produced from alkanes by

cracking ( heating the alkane with a catalyst)


27/34

Polymers

Examples: polythene , polypropene

Monomers (ie ethene) are used to form

polymers

Ethene can become polyethene by heating it

under pressure


28/34

Thermosets and thermoplastics

Thermosetsare plastics that are resistant toheat. Used for kettles, saucepan handles etc.Have strong cross linkages which hold the

structure together and make them resistant toheat make them resistant to heat

Thermoplasticsare plastics that soften whenheated. Used for packaging, containers. Madeup of polymer chains not linked together so theycan slide over each other


29/34

Water TreatmentWhen the water is inthe reservoir, the largeparticles will sink tothe bottom(sedimentation), the

smaller particles willbefiltered.

The water ischlorinated to kill the

bacteria to make itsafe to drink. Fluorideis also added

It is then stored until it

is needed


30/34

DesalinationDefinition: The removal of salt from sea water so it can be

used for drinkingThis is usually done by reverse osmosis which goes through a

membrane that lets water molecules through but not salt

Problems

- Lots of energy required

- Produces a lot more greenhouse gases

- Expensive

- Very salty water is left when fresh water is used

- Poor countries that have droughts cannot afford this

- Some countries dont have access to the sea


31/34

Extracting waterIf something is dissolved in water,

you can extract it by evaporating

& condensing

To separate a liquid from water

you need to use distillation.

Different liquids have differentboiling points . If you heat an

ethanol and water mixture, the

boiling point of ethanol is 78C so

by heating the mixture at thistemperature the ethanol will

evaporate and when the ethanol

vapour reaches the condenser it

will be cooled and become a

liquid


32/34

Chromatography

Paper Chromatography- a drop of mixtureis placed on the Chromatography paperand placed in a solvent used to dissolvepigment. The solvent soaks into the paperand moves upwards. The more soluble willtravel with the solvent and move furtherup the paper.

The R value is used to measure this

(distance substance travelled/ distance solvent travelled)f

Gas Chromatography- can be used to detect pollutants in water or

air and it is also used to test for banned substances in sports

players. The mixture must be in the form of a gas (vaporised or

naturally occurring.) The gas passes through a column and different

substances are absorbed into an inert solid or liquid. The position

the chemical moves along the column is detected electronically


33/34

Hard water

Hard water contains dissolved calcium and magnesium ions.Can be temporary or permanent

Temporary hard water contains magnesium/calcium hydrogencarbonates . When heated the hardness is removed but it formscalcium carbonate (scale) which clogs up pipes.

Permanent hard water contains chlorides/sulphates of calciumand magnesium which does not soften when heated

Advantages of hard water

-Some people prefer the taste

-Calcium is good for teeth and bones-Helps reduce heart illness

- Some brewers use hard water in beer

Disadvantages of hard water

-Difficult to form lather with

soap-Scum forms with soap

- Scale forms, clogs pipes

and kettles


34/34

How to soften hard water

1. Boiling- easy and cheap but doesnt work forpermanent hardness

2. Adding Sodium Chloride- prevents calcium and

magnesium ions bonding with washing detergent.

Cheap, removes permanent hardness but deposits

are still formed

3. Ion exchange column- Column filled with resin

which has sodium ions. The calcium/magnesiumions are swapped for the sodium ions and come out

of the tube with the water where as the calcium

ions remain in the resin. Can treat a large amount of

t b t i

Documents

Review of Chemistry