Chemistry

GCSE AQA Additional Chemistry

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Ionic

The losing or gaining of electrons.

Ionic compounds are made up of giant ionic lattices, the ions are tightly packed and have strong electrostatic forces of attraction.

Their properties are HIGH melting and boiling point, dissolve easily in water and carry electric current.

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Covalent

The sharing of electrons so both atoms have a full outer shell

Simple molecular substances. Atoms form strong covalent bonds to form small molecules that have weak forces of attraction.

These forces are broken easily when boiled or melted (low boiling and melting point), they dont conduct electricity because theres no ions and charge

GIANT covalent structures similar to lattices but have no ions/charge. Strong covalent bonds

e.g;

diamond- strong, hard, rigid, 4 bonds

silicon dioxide- makes sand

graphite- soft and slippery, 3 bonds, weak intermolecular forces between layers, layers slide over eachother, can be rubbed off (pencil)

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Metallic Structure

Metalic bonds involve free ions, made up of strong electrostatic forces of attraction between metal ions (+) and electrons (-).

Metals are good conductors of heat and electricity

Alloys are stronger than pure metals as they're a mixture of metals

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Smart Materials

Behave in certain ways depending on condition 

e.g; Nitinol- Flexible, bend it too far and it stay bent but when heated turns back to remembered shape

...Used for braces and glass frames

NANOPARTICLES (tiny particles containing a few 100 atoms)

- Include fullerenes (carbon molecules) which form to make nanotubes

USES OF NANOSCIENCE: Catalysts, cosmetics, circuits, lube for artificial joints,   sensors, strong light building material

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Polymers

Thermosoftening plastics - Weak intermolecular forces, when heated are    remouldable (chains free to slide over eachother)

Thermosetting plastics - Strong intermolecular forces, chains tightly packed.        Doesn't soften when heated

LD POLYETHENE- High temp and pressure, used for plastic bags

HD POLYETHENE - Low temp and pressure, used for tanks

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Equations

RFM = RAM added together

RAM = biggest number on element 

MOLES are the relative formula mass in grams

Moles = Mass/RFM

MASS OF A COMPOUND

RAM X NO OF ATOMS

---------------------------- X 100

   RFM

EMPIRICAL FORMULA

find % of elements then divide that by their RAM then find the ratio

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Reactions

PRECIPITATION - When products cloud the solution, observe the solution and see how long marks take to dissapear, faster it dissapears the faster the reaction

CHANGE IN MASS - gas released in a reaction reduces the mass, quicker mass drops, the faster the reaction

VOLUME OF GAS GIVEN OFF - Syringe measure this, more gas given off, the faster the reaction, syringe is to nearest MM so it's accurate

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Rate of reaction experiments

HYDROCHLORIC ACID AND MARBLE CHIPS REACTION

Gas given out is measured with syringe

Plot in a table

Repeat experiment with crushed marble, then marble powder

Marble powder, faster reaction (bigger surface area, frequent collisions)

Marble chips, slower reaction (smaller surface area)

MAGNESIUM METAL AND HYDROCHLORIC ACID REACTION

Hydrogen gas is given off, good for measuring effects of high concentration

SODIUM THIOSULFATE + HCL --> CLOUDY PRECIPITATE

Both chemicals clear solution, react to form yellow precipitate of sulfur

DECOMPOSITION OF HYDROGEN PEROXIDE

2 h2 o2 <----> 2 h20 + o2

Slow reaction but manganese oxide catalyses reaction


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Collision Theory

High temp, concentration and large surface area = more collisions & faster reaction

Reaction only happens with enough energy, minimum energy is activation energy.

CATALYST - Speed up reaction without being used up or changed

+ Reduce need for high temps in reaction (less money)

Increases reaction rate, saving money

have to buy many cause each catalyst is specific to reaction

expensive

can stop working

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Exothermic and endothermic

Exothermic - energy exits reaction,  transferring energy and heating up surroundings 

e.g; hand warmers and self heating cans

Endothermic -energy enters reaction taking energy from surrounds and temp of them falls

e.g; thermal decomposition and sports injury packs

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Acids and alkalis

Below PH7 = acid

Above PH7 = alkakli

Base is a substance with a bigger ph than 7, alkali is a base disolved in water

H+ = Acid      OH- = Alkali

Acid + Base = Salt + Water (Neutralisation)

Acid + Metal = Salt + Hydrogen

Acid + Metal (hydr)oxide = Salt + Water

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Making Salts

Pick the right acid + metal (base, oxide or hydroxide). 

This will make the solid dissolve in the acid

Acid is neutralised when solid sinks to bottom of the flask

Filter the metal out to get salt, get purer salt by evaporating water then leave rest to evaporate slowly CRYSTALLISATION

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