AQA GCSE Chemistry - Paper 1

What pattern is formed from carrying out paper chromatography?

Chromatogram

Which method of separation is useful to separate an insoluble solid from a liquid?

Filtration

Which method of separation is useful to separate a soluble solid from a liquid?

Evaporation or Crystillisation

Which method of distillation separates liquids with similar boiling points?

Fractional distillation

Who discovered that the plum pudding model was wrong?

Ernest Rutherford

Who devised an experiment that proved the existence of the neutron?

James Chadwick

Why did Mendeleev leave gaps in his Table of Elements?

To ensure that elements with similar properties stayed in the same groups. The gaps indicated the existence of undiscovered elements and allowed Mendeleev to predict what their properties might be

State three trends as you go down Group 1

1) Increased reactivity - the outer electron is more easily lost as the attraction between the nucleus and the electron decreases because the electron is further away from the nucleus

2) Lower melting and boiling points

3) Higher relative atomic mass

What are the products of the reaction of a Group 1 metal and water

Hydrogen gas and a metal hydroxide

E.g. sodium + water --> sodium hydroxide + hydrogen

What trends occur as you go down Group 7?

1) They become less reactive - it's harder to gain an extra electron because the outer shell's further from the nucleus

2) They have higher melting and boiling points

3) They have higher relative atomic masses

What is the charge of the ions that halogens form when they react with metals?

They form negative ions

What is the trend in boiling point as you go down Group 0?

The boiling points increase

What subatomic particles does the nucleus contain?

Protons and neutrons

What is relative atomic mass?

The mass number which refers to the element as a whole

How are positive ions formed?

A metal atom loses electrons

How are negative ions formed?

A non-metal gains electrons

What is crude oil a mixture of?

Different length hydrocarbon molecules

How can you separate substances in a mixture?

Chromatography

What is simple distillation used for?

Separating out a liquid from a solution

E.g. separating pure water from seawater

How were elements arranged in the early 1800s?

By their physical and chemical properties and their relative atomic mass

How are columns arranged?

Elements with similar properties

What are the three similar basic properties of metals?

1) They're strong but are malleable

2) They're great at conducting heat and electricity

3) They have high boiling and melting points

What is the product of the reaction of a Group 1 metal with chlorine?

A metal chloride salt

E.g. sodium + chlorine --> sodium chloride

What is the product of the reaction of a Group 1 metal with oxygen?

A metal oxide, depending on the Group 1 metal

-Lithium + oxygen --> lithium oxide

-Sodium + oxygen --> sodium oxide + sodium peroxide

-Potassium + oxygen --> potassium peroxide + potassium superoxide

What are halogens?

Non-metals in Group 7 with coloured vapours

What do halogens exist as?

Molecules - pairs of atoms

What do halogens form?

1) Molecular compounds - halogens share electrons via covalent bonding with other non-metals too achieves a full outer shell

2) Ionic compounds with metals - they form 1- ions called halides

What are the noble gases at room temperature?

Colourless gases

Are the noble gases flammable?

No - they're non-flammable

Why does the boiling point of noble gases increase as you move down the group?

There's an increase in the number of electrons in each atom leading to greater intermolecular forces between them which to be overcome

Paper Chromatography - Method

1) Draw a pencil line near the bottom of a sheet of filter paper

2) Add a spot of ink to the line & place the sheet in a beaker of solvent e.g. water - the solvent used depends on what's being tested - some compounds dissolve well in water, but sometimes other solvents e.g. ethanol are needed

3) Ensure the ink isn't touching the solvent - you don't want it to dissolve

4) Place a lid on top of the container to stop the solvent evaporating

5) The solvent seeps up the paper, carrying the ink with it

6) Each different dye in the ink will move up the paper at a different rate so that the dyes will separate out - each dye will form a spot in a different place, 1 spot per dye in the ink

7) If any of the dyes in the ink are insoluble in the solvent used, they'll stay on the baseline

8) When the solvent has nearly reached the top of the paper, take the paper out of the beaker & leave it to dry

Simple Distillation - Method

1) The solution is heated. The part of the solution that has the lowest boiling point evaporates first

2) The vapour is then cooled, condensed & is collected

3) The rest of the solution is left behind in the flask

What is the problem with simple distillation?

You can only use it to separate things with very different boiling points - if the temperature goes higher than the boiling point of the substance with the highest boiling point, they will mix again

Fractional Distillation - Method

1) Put a mixture in a flask & stick a fractionating column on top and heat it

2) The different liquids all have different boiling points - they'll evaporate at different temperatures

3) The liquid with the lowest boiling point evaporates first. When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column

4) Liquids with higher boiling points might also start to evaporate, but the column is cooler towards the top, therefore they will only get part of the way up before condensing & running back down towards the flask

5) When the first liquid has been collected, you raise the temperature until the next one reaches the top

Describe how an ionic bond forms

When a metal and a non-metal react together, the metal loses its one electron on its outer shell to form a positively charged ion. This one electron is gained by the non-metal to complete its outer shell, forming a negative ion.

Describe the structure of a crystal of sodium chloride

It's a giant ionic lattice. The positive sodium and negative chlorine ions form a closely packed regular arrangement and there are very strong electrostatic forces of attraction between the oppositely charged ions.

List the main properties of ionic compounds

1) High melting and boiling points - many strong bonds between the ions

2) They can't conduct electricity when they're solid - the ions are held in a fixed arrangement therefore they can't pass on the electrical current.

3) They can conduct electricity when they're liquids because the ions are free to move therefore they can pass on the electrical current.

4) They dissolve easily in water - they are free to move in the solution and can carry electrical current.

Describe how covalent bonds form

When two non-metals bond together, they share electrons to make covalent bonds. The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces - this makes covalent bonds very strong.

Explain why simple molecular compounds typically have low melting and boiling points

The intermolecular forces between the atoms are very weak, therefore it takes only a small amount of energy to break them apart.

Describe the structure of a polymer

Polymers are long chains of repeating units joined together to make a long molecule. Between the atoms are strong covalent bonds.

Give three examples of giant covalent substances

-Diamond

-Graphite

-Silicon Dioxide

Explain why graphite can conduct electricity

It contains delocalised electrons which can carry electrical charge

What is metallic bonding?

The electrons in the outer shell of a metal atom are delocalised. There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons. These forces of attraction hold the atoms together in a regular structure.

List three properties of metals and explain how metallic structure causes each property

1)Solid at room temperature - they have very high melting and boiling points because a lot of energy is needed to break the strong electrostatic forces of attraction between the metal atoms and delocalised electrons.

2)Good conductors of heat and electricity - the delocalised electrons can carry electrical current and thermal energy through the structure.

3)Malleable - the layers of metal atoms can slide over each other

Explain why alloys are harder than pure metals

When two metals are mixed together, both of their atoms are different sizes which causes a disruption in the neat layers of metal atoms. This makes it more difficult for the layers to slide over each other.

What is the name of the temperature at which a liquid becomes a gas?

Boiling

Describe giant covalent structures

-All the atoms are bonded to each other by strong covalent bonds

-They have very high melting and boiling points, therefore, lots of energy is required to break the covalent bonds

-Most of them don't conduct electricity because they don't contain delocalised electrons or ions

Describe the structure of diamond

Each carbon atom forms four strong covalent bonds in a very rigid giant covalent structure.

Describe the structure of graphite

Each carbon atom forms three covalent bonds to create layers of hexagons. Each carbon atom also has one delocalised electron.

Describe the properties of diamond

-Very hard because of its structure

-Very high melting point because it takes a lot of energy to break the bonds

-No delocalised electrons, therefore it cannot conduct electricity

What is graphene?

• A sheet of carbon atoms joined together in hexagons

• The network of covalent bonds makes it very strong

• Very light - added to composite materials to improve their strength but not to add weight

• Contains delocalised electrons - conducts electricity through the whole structure

• Can be used in electronics

What are fullerenes?

Molecules of carbon, shaped like closed tubes or hollow balls - the carbon atoms are arranged in hexagons but also pentagons & heptagons

Uses of Fullerenes

1) To 'cage' other molecules - the fullerene structure forms around another atom/molecule, which is then trapped inside - used to deliver drugs into the body

2) Make good industrial catalysts due to their large surface area

3) Make good lubricants

Nanotubes

Tiny carbon cylinders formed from fullerenes

Ratio between length & diameter is very high

Conduct electricity & thermal energy

High tensile strength - don't break when stretched

Used for nanotechnology - used in electronics or to strengthen materials without adding much weight e.g. tennis racket frames

Melting

When a solid is heated, the particles gain more energy which causes them to vibrate - weakens the forces that hold the solid together

At the melting point, the particles will have enough energy to break free from their positions - the solid turns into a liquid

Boiling

When a liquid is heated, the particles will gain even more energy, making them move faster - weakens and breaks the bonds holding them together

At the boiling point, the particles have enough energy to break their bonds - the liquid becomes a gas

Condensing

As a gas cools, the particles no longer have enough energy to overcome the force of attraction between them, causing bonds to form between the particles

At the boiling point, so many bonds have formed between the gas particles that the gas becomes a liquid

Freezing

When a liquid cools, the particles have less energy, so move around less

There's not enough energy to overcome the attraction between the particles, so more bonds form between them

At the melting point, so many bonds have formed between the particles that they're held in place - the liquid becomes a solid

Equation for surface area to volume ratio

Surface area to volume ratio = surface area / volume

Do nanoparticles have a high or low surface area to volume ratio?

Very high surface area to volume ratio - the surface area is very large compared to the volume, therefore, they make good catalysts

Simple Molecular Structures

Very strong covalent bonds

Very weak intermolecular forces

Most are liquids & gases at room temperature

The bigger the molecule, the stronger the intermolecular forces

Don't conduct electricity - no delocalised electrons or ions as they're not charged

Why is Buckminsterfullerene a good lubricant?

It's shaped like a hollow ball, thus it can roll

What is one mole?

An amount of that a substance that contains an Avogadro number of particles

What is the Avogadro constant?

6.02x10²³

Why is the mass conserved during a chemical reaction?

No atoms are created and no atoms are destroyed

When is a reactant limiting?

When it's completed used up in a reaction before the rest and causes the reaction to stop

Why are reactants added in excess?

To ensure that the limiting reactant is used up

What is the amount of product directly proportional to?

The amount of limiting reactant

What happens when you add more reactant?

There will be more reactant particles to take part in the reaction, therefore more product particles

What is concentration?

The amount of a substance in a certain volume of a solution

The more solute there is in a given volume...

...The more concentrated the solution

How do you convert mol/dm³ to g/dm³?

Find the concentration in mol/dm³ then convert the concentration using the equation:

mass = moles x Mr

What is the yield?

The amount of product you get - the more reactants there are, the higher the yield will be

Equation for Percentage Yield

Percentage Yield = mass of product actually made (g) / Maximum theoretical mass of product (g) x 100

Why do industrial processes need a high percentage yield?

It reduces waste and costs

In real life, do you ever get a 100% yield?

No - some product or reactant always gets lost along the way

Problems of getting a 100% yield - Problem 1

Not all reactants react to make a product - in reversible reactions, the products can turn back into reactants, so the yield will never be 100%

Problems of getting a 100% yield - Problem 2

There might be side reactions - the reactants sometimes react differently to how you expect

They might react with gases in the air, or impurities in the reaction mixture, which forms extra products other than the ones you want

Problems of getting a 100% yield - Problem 3

When you filter a liquid to remove solid particles, you nearly always lose a bit of liquid or a bit of solid

If you want to keep the liquid, you'll lose the bit that remains with the solid and filter paper

If you want to keep the solid, some of it'll get left behind when you scrape it off the filter paper

You'll always lose a bit of material when you transfer it from one container to another - some always gets left behind on the inside surface of the old container

What neutralises an acid?

A base (alkali)

Neutralisation equation

Acid + base --> salt + water

What do acids form in water?

Positive hydrogen ions

What do alkalis form in water?

Negative hydroxide ions

Symbol equation of neutralisation

H(positive) + OH(negative) --> H2O

What do strong acids do in water?

They ionise completely - all acid particles dissociate to release positive hydrogen ions

What do weak acids do in solution?

They don't fully ionise in solution - only a small proportion of acid particles dissociate to release positive hydrogen ions

Examples of strong acids

Sulfuric acid

Hydrochloric acid

Nitric acid

Examples of weak acids

Ethanoic acid

Citric acid

Carbonic acid

How do acids react?

The positive hydrogen ions react with other substances

What happens if the concentration of positive hydrogen ions is higher?

The rate of reaction will be faster, therefore strong acids will be more reactive than weak acids of the same concentration

What is pH?

A measure of the concentration of positive hydrogen ions in the solution

For every decrease of 1 on the pH scale...

...The concentration of positive hydrogen ions increase by a factor of 10 - Logarithmic

E.g. pH 4 has 10 times the concentration of pH 5

What does acid strength tell you?

What proportion of the acid molecules ionise in water

Are metal oxides and hydroxides bases or acids?

Bases

Are metal carbonates bases or acids?

Bases

Equation with a metal carbonate

Acid + metal carbonate --> salt + water + carbon dioxide

Reactivity series

Potassium

Sodium

Lithium

Calcium

Magnesium

Aluminium

CARBON

Zinc

Iron

Tin

Lead

HYDROGEN

Copper

Silver

Gold

Platinum

Metals that react with water out of the RS

Potassium, sodium, lithium and calcium

Metals that don't react with water out of the RS

Zinc, iron and copper

Oxidation =

Gain of oxygen

Loss of electrons