GCSE Chemistry Syllabus

Compare the structure and properties of diamond and graphite.

Both are giant covalent carbon structures. In diamond each carbon forms 4 bonds, making it very hard with no free electrons (non-conductor). In graphite each carbon forms 3 bonds in layers that slide, and delocalised electrons let it conduct electricity.

What are the properties and uses of graphene and fullerenes?

Graphene is a single layer of graphite: strong, light and conducts electricity, used in electronics/composites. Fullerenes (e.g. $\ce{C60}$ buckminsterfullerene) are hollow cages/tubes used for drug delivery, catalysts and nanotubes for strength/electronics.

Why can metals be bent and shaped, and why do they conduct electricity and heat?

Layers of positive ions can slide over each other, so metals are malleable. Delocalised electrons are free to move and carry electrical charge and thermal energy through the metal.

Write the general word equation for a metal reacting with an acid.

Metal + acid $\rightarrow$ salt + hydrogen. For example $\ce{Mg + H2SO4 -> MgSO4 + H2}$.

State the reactivity series from potassium to gold (key metals plus carbon and hydrogen).

Potassium, sodium, lithium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold. More reactive metals lose electrons to form positive ions more readily.

What is a displacement reaction and what determines whether one occurs?

A more reactive metal displaces a less reactive metal from its compound. E.g. $\ce{Fe + CuSO4 -> FeSO4 + Cu}$. It occurs only if the added metal is more reactive than the one in the compound.

Define oxidation and reduction in terms of electrons (OIL RIG).

Oxidation Is Loss of electrons; Reduction Is Gain of electrons. In $\ce{Mg -> Mg^2+ + 2e-}$ magnesium is oxidised; in $\ce{Cu^2+ + 2e- -> Cu}$ copper ions are reduced.

How are metals extracted from their ores depending on reactivity?

Metals less reactive than carbon (e.g. iron, zinc) are extracted by reduction with carbon. Metals more reactive than carbon (e.g. aluminium) are extracted by electrolysis of molten compounds.

Give the equation for the reduction of iron oxide by carbon in the blast furnace.

$$\ce{2Fe2O3 + 3C -> 4Fe + 3CO2}$$ The iron oxide is reduced (loses oxygen) and carbon is oxidised.

What is electrolysis?

Electrolysis is the breaking down of an ionic compound (molten or in solution) using an electric current. Positive ions move to the cathode and negative ions move to the anode, where they are discharged.

During electrolysis, what happens at the cathode and at the anode?

At the cathode (negative electrode) positive ions gain electrons and are reduced. At the anode (positive electrode) negative ions lose electrons and are oxidised.

Why must ionic compounds be molten or dissolved for electrolysis?

So that the ions are free to move to the electrodes and carry the current. In a solid the ions are held in fixed positions and cannot move.

For the electrolysis of an aqueous solution, what is produced at the cathode?

Hydrogen is produced unless the metal is less reactive than hydrogen (e.g. copper), in which case the metal is deposited. The less reactive ion is discharged in preference.

For the electrolysis of an aqueous solution, what is produced at the anode?

A halogen ($\ce{Cl2}$, $\ce{Br2}$, $\ce{I2}$) is produced if a halide is present; otherwise oxygen is produced from hydroxide/water. E.g. $\ce{2Cl- -> Cl2 + 2e-}$.

Why is cryolite used in the electrolysis of aluminium oxide?

Aluminium oxide is dissolved in molten cryolite to lower its melting point, reducing the energy (and cost) needed to keep the mixture molten.

Write the half equations for the electrolysis of molten aluminium oxide.

Cathode: $\ce{Al^3+ + 3e- -> Al}$. Anode: $\ce{2O^2- -> O2 + 4e-}$. The carbon anodes burn away as they react with oxygen.

Define exothermic and endothermic reactions in terms of energy transfer.

An exothermic reaction transfers energy to the surroundings (temperature rises), e.g. combustion. An endothermic reaction takes in energy from the surroundings (temperature falls), e.g. thermal decomposition.

On a reaction profile, how do you tell an exothermic from an endothermic reaction?

In an exothermic reaction the products are at a lower energy than the reactants ($\Delta H$ negative). In an endothermic reaction the products are at a higher energy than the reactants ($\Delta H$ positive).

What is activation energy?

The minimum energy that colliding reactant particles must have for a reaction to occur; on a reaction profile it is the height from the reactants up to the peak of the curve.

How is the overall energy change of a reaction calculated from bond energies?

$$\Delta H = \sum E_{\text{bonds broken}} - \sum E_{\text{bonds made}}$$ Breaking bonds is endothermic; making bonds is exothermic.

What is a hydrocarbon, and what is the general formula of the alkanes?

A hydrocarbon is a compound containing only hydrogen and carbon atoms. Alkanes are saturated hydrocarbons with the general formula $\ce{C_{n}H_{2n+2}}$, e.g. methane $\ce{CH4}$.

Describe how the properties of hydrocarbons change as the molecules get larger.

As chain length increases: boiling point rises, viscosity increases, flammability decreases, and the fractions become less volatile.

How does fractional distillation separate crude oil?

Crude oil is heated and vaporised, then enters a fractionating column with a temperature gradient (hot at bottom, cool at top). Hydrocarbons condense and are collected at the height where the temperature matches their boiling point.

Write the general equation for the complete combustion of a hydrocarbon.

Hydrocarbon + oxygen $\rightarrow$ carbon dioxide + water. E.g. $$\ce{CH4 + 2O2 -> CO2 + 2H2O}$$ Both carbon and hydrogen are oxidised.

What is cracking and why is it carried out?

Cracking breaks long-chain hydrocarbons into shorter, more useful ones using heat with a catalyst (catalytic) or steam. It produces smaller alkanes (fuels) and alkenes (for polymers) to match demand.

What is the general formula of alkenes and how are they tested for?

Alkenes are unsaturated hydrocarbons with a $\ce{C=C}$ double bond, general formula $\ce{C_{n}H_{2n}}$. They decolourise orange bromine water (from orange to colourless).

Describe how addition polymers are formed from alkene monomers.

Many small unsaturated monomers with $\ce{C=C}$ double bonds join together in an addition reaction, the double bonds opening to form a single long saturated polymer chain, e.g. ethene forms poly(ethene).

How does condensation polymerisation differ from addition polymerisation?

Condensation polymerisation involves monomers with two functional groups reacting and joining together with the loss of a small molecule (usually water) for each bond formed. Addition polymerisation loses no small molecule and uses monomers with a $\ce{C=C}$ bond.

State the functional group of alcohols and give the first four members.

The functional group is $\ce{-OH}$ (hydroxyl). The first four are methanol, ethanol, propanol and butanol; e.g. ethanol is $\ce{C2H5OH}$.

What are the products when ethanol is oxidised, and what functional group do carboxylic acids contain?

Ethanol is oxidised to ethanoic acid (a carboxylic acid). Carboxylic acids contain the $\ce{-COOH}$ functional group; e.g. ethanoic acid is $\ce{CH3COOH}$.

Define a pure substance in chemistry and describe how purity is checked using melting point.

A pure substance is a single element or compound not mixed with any other substance. A pure substance melts (and boils) at a specific sharp temperature; impurities lower the melting point and make it melt over a range.

What is a formulation? Give two examples.

A formulation is a mixture made in specific, measured quantities so that each component gives the product the required properties. Examples include paints, fuels, medicines, cleaning products, alloys and fertilisers.

Explain how paper chromatography separates a mixture.

Components dissolve in the mobile phase (solvent) and move up the paper (stationary phase). More soluble components that are less attracted to the paper travel further, so the mixture separates into spots.

How is an $R_f$ value calculated in chromatography?

$$R_f = \frac{\text{distance moved by substance}}{\text{distance moved by solvent}}$$ The value is always between 0 and 1 and is characteristic of a substance in a given solvent.

How do you use chromatography to tell whether a substance is pure?

A pure substance produces only one spot on the chromatogram in all solvents, whereas a mixture separates into two or more spots.

Describe the flame test colours for lithium, sodium, potassium, calcium and copper ions.

Lithium: crimson/red. Sodium: yellow. Potassium: lilac. Calcium: orange-red. Copper: green (blue-green).

How do you test for and identify the gas carbon dioxide?

Bubble the gas through limewise (calcium hydroxide solution); carbon dioxide turns the limewater cloudy/milky: $$\ce{Ca(OH)2 + CO2 -> CaCO3 + H2O}$$

Describe the tests for hydrogen, oxygen and chlorine gases.

Hydrogen: a lighted splint gives a squeaky pop. Oxygen: relights a glowing splint. Chlorine: bleaches damp blue litmus paper (turns it white, sometimes red first).

How are carbonate, sulfate and halide ions identified in solution?

Carbonate: add dilute acid, effervescence of $\ce{CO2}$ that turns limewater cloudy. Sulfate: add dilute HCl then barium chloride, a white precipitate forms. Halide: add dilute nitric acid then silver nitrate, giving white ($\ce{Cl-}$), cream ($\ce{Br-}$) or yellow ($\ce{I-}$) precipitate.