Chemistry C4 - C6

Question 1

Group 1 - Alkali Metals

Answer 1

Are very reactive - readily lose 1 electron in the outer shell
Reaction with old water produces hydroxide and hydrogen gas
2Na + H2O –> 2NaOH + H2
Sodium + Water –> sodium hydroxide + hydrogen

Question 2

Group 7 - Halogens

Answer 2

Group 7 elements, or halogens, readily gain 1 electron to have a full outer shell. They exist as diatomic molecules, sharing one pair of electrons in a covalent bond

As you go down the group, reactivity decreases

Halogens react with alkali metals to form salts

Question 3

Halogen Displacement Reactions

Answer 3

A more reactive halogen will displace a less reaction one. For example, chlorine will displace bromine because it is higher up in the periodic table/

Cl2 + 2KBr –> Br2 + 2KCl

These reactions can be used as an indicator:
KCl2 - Colourless
KBr2 - Orange
KI2 - Brown

Question 4

Group 0 - Noble gases

Answer 4

Group 0 elements are all inert, colourless gases.

They are non flammable and inert, so it is difficult to identify any changes

Question 5

Transition Metals

Answer 5

Transition metals have typical metallic properties. These metals and their compounds make good catalysts (such as iron)

Transition metals often have more than one Ion - Fe2+ and Fe3+

They are also relatively unreactive

Question 6

Reactivity of Metals

Answer 6

Metals can react with acids to tell you how reactive they are. The more reactive the metal is, the faster the reaction will go.

For example, reacting metals with dilute hydrochloric acid (HCl). The amount of bubbles given off in a certain time span can show the rate of reaction.

Metal + water –> Metal Oxide + Hydrogen

Question 7

The reactivity series and displacement

Answer 7

A more reactive metal will displace a less reactive one.
Copper sulfate + iron –> iron sulfate + copper

(Most reactive)
Potassium - K
Sodium - Na
Calcium - Ca
Magnesium - Mg
Aluminium - Al
Zinc - Zn
Iron - Fe
Copper - Cu
Silver - Ag
(Least reactive)

Question 8

Tests for gases

Answer 8

Carbon dioxide - Limewater turns cloudy

Hydrogen - A lighted splint. A squeaky pop will be heard

Oxygen - A glowing split will relight

Chlorine - Damp litmus paper will turn white if chlorine is present

Question 9

Test for anions (Triple)

Answer 9

Test for halide ions using Silver Nitrate Solution:
Chloride - White precipitate
Bromide - Cream precipitate
Iodide - Yellow precipitate
All of these will form Silver [halide ion] - E.g. Silver Chloride

Carbonates using Hydrochloric acid:
If there are carbonate ions present, the mixture will fix; carbon dioxide gas will be formed

Sulfate ions using Barium Chloride solution:
Sulfate ions react with barium ions and if a white precipitate, barium sulfate, is formed, then the sulfate ions are present

Question 10

Test for Cations (Triple)

Answer 10

Typically, flame test are used for this.
Lithium/Li+ - Crimson red flame
Sodium/Na+ - Yellow flame
Potassium/K+ - Lilac flame
Calcium/Ca2+ - Brick red flame
Copper/Cu2+ - Blue-green flame

Some metal ions form a coloured precipitate with sodium hydroxide

Calcium - White precipitate
Copper - Blue precipitate
Iron(II) - green precipitate
Iron(III) - Brown precipitate

Question 11

Chemical Analysis (Triple)

Answer 11

You can use machines to analyse substances. They are very fast, sensitive and accurate, giving you the best possible reading

Infrared spectroscopy: This technique produces a graph showing which frequencies of infrared a molecule will absorb

Ultraviolet Spectroscopy:
Similar to Infrared, but uses ultraviolet light

Gas chromatography:
Used to separate out the chemicals in a mixture

Mass spectroscopy: A technique used to find the relative molecular mass of a mystery compound

Question 12

Concentration

Answer 12

Concentration is a measure of how crowded things are.

Concentration = mass of solute / volume of solution

Question 13

Titrations (Triple)

Answer 13

Titrations are used to find out concentrations that are unknown.
The pipette is filled with a set volume of the alkali you want to find the concentration with. A few drops of indicator is added to this
A burette is filled with the acid that we know the concentration of. Small drops of the acid is put into the beaker with the alkali until the colour completely changes. The volume of acid that was used to do this is measured and the concentration can be figured out with this formula.
Concentration = number of moles / volume of solution

Question 14

Calculations with gases (Triple)

Answer 14

Molar Volume is the volume occupied by one mole of a gas
molar volume = gas volume / number of moles

Molar volumes are the same under the same conditions (RTP), and that is 24. Therefore:
Volume = 24 x moles
V = 24n

Question 15

Percentage yields and atom economy (Triple)

Answer 15

Percentage yield compares actual yield and theoretical yield.

Percentage yield = (Actual yield / Theoretical yield) x 100

Atom economy is the percentage of reactants changed to useful products

Atom economy = (total Mr of desired produces / total Mr of all products) * 100

Question 16

Reaction rates - Includes experiments

Answer 16

Rate of reaction = amount of reactant used or amount of product formed / time

You can do the following experiments to follow reaction rates:
Precipitation - Two solutions are mixed on top of a paper with an X, and the rate of reaction is how long it takes for the X to disappear
Change in mass (usually gas) - This is quite simple. A reaction occurs and the amount of of mass that is lost can indicate the rate of reaction
A volume of gas given off - This is similar to the last one but involved a gas syringe

Question 17

Rate Experiments

Answer 17

Reaction of Hydrochloric acid and Marble chips - gas is produced in a syringe
Finer particles of solid mean higher rate of reaction; larger rate of reaction

Reaction of magnesium metal with dilute Hydrochloric Acid. More concentrated solutions mean a higher rate

Question 18

Calculating rates

Answer 18

Rates can be calculated by the gradient of a graph. If the graph is curved, draw a tangent.

1 / time is proportional to rate (rate is inversely proportional to time)

Question 19

Collision Theory

Answer 19

Particles must collide with enough energy in order to react
The more successful collisions, the higher the rate of reaction
Increasing the temperature and concentration (pressure) increases rate. Smaller solid particles, or more surface area, means a higher rate

Question 20

Catalysts

Answer 20

Catalysts increase the rate of reaction. They do this by decreasing the activation energy required for the reaction. They aren’t used up so only a tiny bit is needed.

Question 21

Dynamic Equilibrium

Answer 21

Reversible reactions can go forwards and backwards, and are presented by the symbol ⇌.
Reversible reactions will reach equilibrium. As the reactants react, their concentrations fall - so the forward reaction will slow down. But as more and more of the products are made and their concentrations rise, the backward reaction will speedup. At equilibrium both reactions are still happening but there’s no overall effect - it’s a dynamic equilibrium. This can only happen in a closed system.

Temperature, pressure and concentration impact this

Question 22

Extracting metals from their ores

Answer 22

Metals are extracted from their ores chemically. For some metals, this can be done by reduction with carbon.
If the metal is less reactive than carbon then it can be displaced:
Copper oxide + carbon –> copper + carbon dioxide

Carbon is in between aluminium and zinc in the reactivity series

Question 23

Extracting metals with electrolysis

Answer 23

Some metals, which are more reactive than carbon, are extracted by electrolysis of their molten compounds.

Copper is purified by electrolysis
Copper can be extracted by reduction with carbon (smelting). However, the copper this produces is quite impure, and impure copper doesn’t conduct electricity so we use electrolysis.

The electrolyte (aqueous solution) is copper sulfate in this instance, containing Cu2+ ions. The cathode (negative electrode) will attract the Cu2+ ions to it, surrounding the rod with pure copper

Question 24

Biological Extraction Methods

Answer 24

Bioleaching - This uses bacteria to separate metals from their ores. The bacteria get energy from the bonds between the atoms in the ore, separating out the metal from the ore in the process (I don’t think you have to know about this but it’s there in my book)

Phytoextraction - Plants are grown in soil that contain metal compounds. The plant cant get rid of these of the metals so it builds up in the leaves. The plant is then harvested, dried and burned, leaving ash that contains the metal compounds that can be extracted by electrolysis or displacement reactions

Question 25

Alloys (Triple)

Answer 25

An alloy is a mixture of a metal and other elements.
Steel is an alloy of iron and carbon - A lot harder and stronger (wont rust either)

Brass - Copper and Zinc
Bronze - Copper and Tin
Solder - Lead and tin
Duralumin - 94% aluminium, 4% copper, 1% of magnesium and small amounts of manganese

Question 26

Corrosion (Triple)

Answer 26

Rusting of iron is a redox reaction.
Iron + oxygen + water –> hydrated iron(III) oxide

Iron loses electrons when it reacts with oxygen to become Fe3+ so it’s oxidised
Each O atom gains two electrons to become O2-, so oxygen is reduced

Oil, grease and paint can prevent corrosion (keeps oxygen and water out)
A coat of tin can protect steel
More reactive metals can prevent metals corroding

Question 27

The Haber Process (Triple) - This one is quite a long flash card so spend time on it

Answer 27

Nitrogen and hydrogen can react to make Ammonia
N2 (g) + 3H2 (g) ⇌ 2NH3 (g) (+ heat)
This reaction is at equilibrium
Nitrogen can be obtained from the air (78% of the air is nitrogen)
Hydrogen can be obtained from hydrocarbons (natural gas or crude oil)

In industry, ammonia is made at a pressure of 200 atm and a temperature of 450°C in the presence of an iron catalyst (doesn’t affect the position of equilibrium)
Higher pressures allow the forward reaction to occur faster, so the highest possible pressure is used.
The forward reaction is exothermic, which means that increasing the temperature will move the equilibrium the wrong way (away from ammonia and toward nitrogen and hydrogen), so the lowest temperatures are used that don’t impact the rate of reaction too much. 450°C is the best compromise

Question 28

Fertilisers (Triple)

Answer 28

Fertilisers can help plants grow. The three main essential elements are nitrogen, phosphorus and potassium - Fertilisers replace the missing elements in the soil to increase crop yield

Ammonia can be neutralised with acids to produce fertilisers. Ammonia is a base and can be neutralised by acids to make ammonium salts. Nitric acid and ammonia form ammonium nitrate which is very good because it has a high percentage of nitrogen
Ammonium sulfate and ammonium phosphate are also very good fertilisers
Potassium nitrate is also a fertiliser - can be make by neutralising nitric acid with potassium hydroxide.

Question 29

Preparing Ammonium Sulfate in the lab - Experiment (Triple)

Answer 29

The burette is filled with sulfuric acid and the flask is filled with ammonia solution + methyl orange indicator
Slowly add drops of sulfuric acid into the flask. Methyl orange is yellow in alkalis, but red in acids, so this colour change means that all the ammonia has been neutralised and ammonium sulfate has been made.
However, the indicator is still in there so the solution isn’t pure. To overcome this, you note how much acid was needed to neutralise the ammonia solution and repeat the experiment without the indicator.
To get solid ammonium sulfate crystals, gently evaporate the solution until only a little bit is left, then leave it to crystallise. The crystals are then filtered out and dried, leaving you with a solid

Question 30

The Contact Process (Triple)

Answer 30

The contact process is used to make sulfuric acid.
The first stage is o make sulphur dioxide (SO2) - usually by burning sulphur in the air.
S(s) + O2 (g) –> SO2

The sulphur dioxide is then oxidised (with the help of a catalyst) to make sulphur trioxide (SO3)
2SO2 + O2 ⇌ 2SO3

Next, the sulphur trioxide is used to make sulfuric acid
SO3 + H20 –> H2SO4

Step 2 is a reversible reaction, so the conditions can be controlled to change the equilibrium position.
Temperature - The reaction is exothermic, so to get maximum yield the temperature must be reduced, but not so much that the rate of reaction is slowed down. Similarly to the Haber process, 450*C is used

Pressure - Increasing pressure is quite expensive, so it is normally kept at atmospheric pressure, or just above

Catalyst - To increase the rate of reaction a vanadium pentoxide catalyst is used (V2O5)

Question 31

Industrial Processes (Maybe Triple)

Answer 31

This is pretty self explanatory so don’t spend much time on it

When designing an industrial process, you should consider:
Cost of raw materials 
Availability of raw materials
Energy costs
Rate
Equilibrium position

Question 32

Life-Cycle Assessments (Not important)

Answer 32

This pretty much is about the environment costs of industrial processes
You consider:
- Materials and manufacture
- Transport 
- Product use
- Disposal

Question 33

Types of materials and their uses (Triple)

Answer 33

There are lots of different types of polymers, and each of them are useful for different things

Ceramics are stiff but brittle. They are made by baking substances such as clay - Glass, porcelain, bone china etc

Composites are made of different materials. One material (the reinforcement) is embedded in another (the matrix/binder) - Fibreglass, concrete, kevlar, etc. These tend to be expensive but very strong and light

Polymers and metals are the other two, which i’m sure you know quite a bit about

Ceramics are insulators of heat and electricity, and they don’t degrade/corrode. They are also strong and hard wearing.

Composites are very strong and are used to reinforce things

Metals are good conductors of heat and electricity. They are malleable but corrode easily

Question 34

Alkanes (Half of this is triple)

Answer 34

Alkanes are saturated hydrocarbons. They are a homologous series of hydrocarbons - they contain only carbon and hydrogen atoms
Their general formula is CnH2n + 2 - CH4 (methane), C2H6 (ethane), C3H8 (propane) etc

They typically take part in combustion reactions
C2H6 + 3.5O2 –> 2CO2 + 3H20
However, if there is a limited supply of oxygen then carbon monoxide is formed instead of carbon dioxide

Question 35

Alkenes (Triple)

Answer 35

Alkenes are unsaturated hydrocarbons; they have a carbon-carbon double bond. This means that the bond can open up, allowing the two carbon atoms to bond with other atoms.

They have the formula CnH2n
I'm gonna try drawing them lol
      H   H        H
H - C - C = C
      H              H
You can test for an alkene using bromine water. When added to bromine water, an alkene will decolourise the bromine water, turning it from orange to colourless. This is because the double bond can open up and form bonds with the bromine.

Alkenes can also be reacted with hydrogen in a process called hydrogenation. This forms an Alkane.

If you are struggling to visualise this, message me on discord and i can send an image

Question 36

Alcohols (Triple)

Answer 36

Alcohols have an -OH functional group
The general formula of an alcohol is CnH2n+1OH
For example, ethanol is C2H5OH
In certain situation this may be written as C2H6O, but that doesn’t show the function -OH group, so refrain to doing this.

Alcohols can be oxidised to form carboxylic acids. You need an oxidising agent, such as potassium manganate(VII)

Question 37

Carboxylic Acids (Triple)

Answer 37

Carboxylic are formed by oxidising alcohols.
They have the general formula Cn-1H2n-1COOH and they have a -COOH functional gruop

Example:
Methanoic acid: HCOOH
Ethanoic Acid: CH3COOH
Propanoic Acid:
C2H5COOH

Question 38

Addition Polymerisation (Triple)

Answer 38

Addition polymers are made from unsaturated monomers, so alkenes for example.

Ethene (C2H4) becomes polyethene (C2H4)n where n is how long the chain is.

When writing out how the polymer looks, remember to remove the double bond present in the monomer and put brackets around it. (Ask me for an image if you don’t understand)

Naming these are quite easy - Just add the word poly before it (polypropene)

Ask Musa for images of all of this

Question 39

Condensation Polymerisation (Triple)

Answer 39

Condensation polymerisation usually involves two different types of monomer.
Each functional group can react with the function group of another monomers, creating long chains of alternating monomers. For each new bond that forms, a small molecule (e.g. water) is lost

Polyesters and Polyamides are examples of condensation polymers

• Polyesters from when carboxylic acid monomers and alcohol monomers react together
• Polyamides are formed from when carboxylic acid and amine monomers react (an amine monomer has nitrogen at the end)

For all of this, ask me for an image

Question 40

Crude Oil

Answer 40

Crude oil is a mixture of lots of different hydrocarbons, mainly alkanes. The different compounds in crude oil are separated by fractional distillation.
Oil is heated until most of it has turned into gas. The gases enter a fractionating column and the liquid bit is drained off at the bottom. In the column, there’s a temperature gradient (it’s hot at the bottom and gets gradually cooler)
The longer hydrocarbons have high boiling points. They turn back into liquid and drain out of the column early on when they’re near the bottom. The shorter hydrocarbons have lower boiling points so they turn into liquids much later on, near the top of the column where it’s cooler.
Each fraction will now have a different length of hydrocarbons, mostly alkanes

Question 41

Extra facts about Crude Oil and Hydrocarbons (Triple)

Answer 41

In crude oil, there are strong covalent bonds between the atoms within each hydrocarbon molecule. There are also intermolecular forces of attraction between different hydrocarbon molecules in the mixture
When the crude oil is heated, the molecules are supplied with extra energy, making the move about more and eventually allow them to overcome the intermolecular forces that keep it with the other other molecules.
The covalent bonds holding each molecule are a lot stronger, so they don’t break.

Intermolecular forces of attraction break a lot more easily in small molecules. That’s why bigger molecules have higher boiling points.

Question 42

Cracking

Answer 42

Cracking is splitting up long-chain hydrocarbons
Cracking turns long alkane molecules into smaller alkane and alkene molecules (which are more useful)
It’s a form of thermal decomposition, which is when one substance breaks down at least two new ones when you heat it. Like we said earlier, each atom has strong covalent bonds so a lot of heat is needed to break their bonds. A catalyst is often used to speed things up.
We usually take the products of fractional distillation and crack them into smaller ones; the demand of something like petrol may be higher than bitumen.
Cracking also produces alkene molecules

Vaporised hydrocarbons are passed over powdered catalyst at about 400 - 700*C and 70 atm
Aluminium oxide is the catalyst that is usually used

Question 43

Fuel Cells (Triple)

Answer 43

Fuel cells use fuel and oxygen to produce electrical energy

A fuel cell is an electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to produce a potential different across the cell, until all the reactants have been used up. Hydrogen and oxygen react to produce water - this is an exothermic reaction.

The hydrogen-oxygen fuel cell releases heat energy and nice clean water, so there’s no pollutants

Hydrogen-Oxygen Fuel cells involve a redox reaction. The electrolyte is often a solution of phosphoric acid. Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment (Ask me for an image). In fuel cells, the anode is negative, which is the opposite of how it is in electrolysis

At the negative electrode, hydrogen loses electrons to produce H+ ions. This is oxidation

At the positive electrode, oxygen gains electrons from the electrode and reacts with H+ ions to make water. This is reduction.

2H2 + O2 –> 2H2O

Fuel cells are quite complicated so just ask me for the image

Question 44

The Atmosphere

Answer 44

Phase 1 - Volcanos gave out steam and CO2
Phase 2 - Green plants evolved and produced oxygen. Nitrogen gas was also put into the atmosphere by the ammonia reacting with oxygen and denitrifying bacteria
Phase 3- Ozone layer formed, allowing evolution of complex animals. This layer blocked harmful rays from the sun.
Our atmosphere is 78% nitrogen and 21% oxygen

Question 45

The Greenhouse Effect

Answer 45

Due to the increasing population of humans, more carbon dioxide was produced. CO2 is a greenhouse gas.

The greenhouse effect helps to keep the earth warm
Greenhouse gases are the gases in the atmosphere that can absorb and re-emit heat radiation. They’re only present in small amounts. Carbon dioxide, water vapour and methane are all examples of this.

If the concentration of greenhouse gases in the atmosphere increases, more heat radiation is absorbed in the earth and the atmosphere heats up, causing global warming

Question 46

Alternative Fuels

Answer 46

Ethanol can be produced from plant material, so it is known as biofuel. It’s made by fermentation of plants and is used to power cars in some places. It’s often mixed with petrol to make a better fuel. It’s carbon neutral but farmers cant produce enough to keep up with demand

Biodiesel is another biofuel. It can be produced from vegetable oils such as rapeseed oil and soybean oil. These are also carbon neutral, but we can’t produce enough to replace diesel

Question 47

Pollutants

Answer 47

Acid Rain - As fossil fuels are burned, harmful gases are produced, such as sulfur dioxide.
This comes from the impurities in the fossil fuels.
These can then mix with clouds, causing acid rain.

Photochemical smog - A type of air pollution caused by sunlight acting on oxides of nitrogen. They produce ozone, which can cause breathing difficulties

Carbon monoxide - As we know, this is a harmful gas as it can stop your blood from carrying oxygen around the body

Question 48

Water Treatment (Triple i think)

Answer 48

Water is purified in water treatment plants. The three methods we can use are:

1) Filtration - A wire mesh screens out large twigs, and then gravel and sand beds filter out any other solid bits
2) Sedimentation - Iron sulfate or aluminium sulfate is added to the water, which makes fine particles clump together and settle at the bottom
3) Chlorination - Chlorine gas is bubbled through to kill harmful bacteria and other microbes