GCSE chemistry - all flashcards

What is a hydrocarbon?

A compound made of only carbon and hydrogen.

How can organic molecules be represented?

Empirical formula, molecular formula, general formula, structural formula, displayed formula.

What is a homologous series?

A family of compounds with the same functional group and similar chemical properties.

What is a functional group?

The part of a molecule responsible for its chemical reactions.

What is isomerism?

Compounds with the same molecular formula but different structural formulas.

What are the main types of organic reactions?

Substitution, addition, combustion.

How do you name organic compounds (up to 6 carbons)?

Using IUPAC rules.

What is crude oil?

A mixture of hydrocarbons.

How is crude oil separated?

Fractional distillation.

Name the main fractions of crude oil.

Refinery gases, gasoline, kerosene, diesel, fuel oil, bitumen.

What is the trend in physical properties of fractions?

As chain length increases: colour darkens, boiling point rises, viscosity increases.

What is a fuel?

A substance that releases heat when burned.

What are the products of complete combustion of hydrocarbons?

CO₂ and H₂O.

What are the products of incomplete combustion?

CO, C, and H₂O.

Why is CO poisonous?

Reduces blood's ability to carry oxygen.

How are oxides of nitrogen formed in car engines?

High temperature allows N₂ + O₂ → NOₓ.

How is sulfur dioxide produced?

Combustion of sulfur impurities in fuel.

How do NOₓ and SO₂ contribute to acid rain?

Dissolve in water to form acids.

What is catalytic cracking?

Breaking long-chain alkanes into shorter alkanes and alkenes using heat and a catalyst.

Why is cracking necessary?

To match supply of fractions with demand (more petrol and alkenes).

What is the general formula for alkanes?

CₙH₂ₙ₊₂.

Why are alkanes saturated?

Only single C-C bonds.

What is the reaction of alkanes with halogens?

Substitution reaction under UV light (mono-substitution).

What is the functional group of alkenes?

C=C (double bond).

What is the general formula for alkenes?

CₙH₂ₙ.

Why are alkenes unsaturated?

Contain at least one double C=C bond.

What is the reaction of alkenes with bromine?

Addition → dibromoalkanes.

How to distinguish alkane vs alkene?

Bromine water: alkene decolorises, alkane does not.

What is the functional group of alcohols?

−OH.

Which alcohols should be known?

Methanol, ethanol, propan-1-ol, butan-1-ol.

How is ethanol oxidised?

1. Combustion → CO₂ + H₂O; 2. Microbial oxidation → ethanoic acid; 3. With K₂Cr₂O₇/H₂SO₄ → ethanoic acid.

How is ethanol manufactured?

1. Hydration of ethene with steam + H₃PO₄; 2. Fermentation of glucose (anaerobic, ~30°C, yeast enzymes).

Why is fermentation anaerobic and at ~30°C?

Anaerobic prevents oxidation; 30°C is optimum for yeast enzymes.

How do you investigate the effect of surface area on rate?

Use marble chips of different sizes reacting with HCl and measure CO₂ volume over time.

How do you investigate the effect of concentration on rate?

React marble chips with different concentrations of HCl and measure gas produced.

How do you investigate the effect of temperature on rate?

Heat/cool a reactant solution and measure time for visible change (e.g., disappearing cross).

How do you investigate the effect of a catalyst on rate?

Decompose H₂O₂ with and without catalyst (e.g., MnO₂) and compare oxygen production.

What is the effect of increased surface area on rate?

Increases rate.

What is the effect of increased concentration on rate?

Increases rate.

What is the effect of increased pressure (gases) on rate?

Increases rate.

What is the effect of increased temperature on rate?

Increases rate.

What is the effect of a catalyst on rate?

Increases rate.

Why does increasing surface area increase rate?

More particles exposed → more frequent collisions.

Why does concentration increase rate?

More particles per volume → more collisions.

Why does pressure increase rate?

Gas particles are closer → more collisions.

Why does temperature increase rate?

Particles have more energy → more frequent + energetic collisions.

What is a catalyst?

A substance that speeds up a reaction but is unchanged at the end.

How do catalysts work?

Provide an alternative pathway with lower activation energy.

How to investigate effect of surface area using marble chips?

React small vs large chips with HCl; measure CO₂ volume/time.

How to investigate concentration using marble chips?

Use different HCl concentrations and measure rate of gas production.

How to investigate catalysts using hydrogen peroxide?

Add different solids (e.g., MnO₂) and measure rate of oxygen release.

What evidence shows Group 1 metals form a family?

They react similarly with water.

What is the trend in Group 1 reactivity?

Reactivity increases down the group.

How do Li, Na and K react with water?

Produce metal hydroxide + hydrogen.

Why does reactivity increase down Group 1?

Outer electron further from nucleus → easier to lose.

How can you predict the reactivity of other alkali metals?

Use group trends.

What is the colour and state of chlorine at room temperature?

Green gas.

What is the colour and state of bromine?

Red-brown liquid.

What is the colour and state of iodine?

Grey solid (purple vapour).

What is the trend in Group 7 physical properties?

Darker and higher melting/boiling points down the group.

What is the trend in Group 7 reactivity?

Reactivity decreases down the group.

What do halogen displacement reactions show?

More reactive halogens displace less reactive halides.

Why does reactivity decrease down Group 7?

Harder to gain electron (more shells → weaker attraction).

What are the four most abundant gases in dry air?

N₂ (~78%), O₂ (~21%), Ar (~1%), CO₂ (~0.04%).

How can oxygen percentage in air be measured?

React oxygen with a metal/non-metal and measure volume decrease.

How does magnesium burn in oxygen?

Bright white flame → magnesium oxide.

How does hydrogen burn in oxygen?

Explosive → water.

How does sulfur burn in oxygen?

Blue flame → sulfur dioxide.

How is CO₂ formed from metal carbonates?

Thermal decomposition.

Why is CO₂ a greenhouse gas?

Traps infrared radiation → warming.

How is the reactivity series determined?

By reactions with water, acids, and displacement reactions.

Which metals are most reactive?

Group 1 metals (K, Na, Li).

What is the order of reactivity from the exam specification?

K > Na > Li > Ca > Mg > Al > Zn > Fe > Cu > Ag > Au.

What conditions are needed for rusting?

Oxygen + water.

How can rusting be prevented?

Barrier method, galvanising, sacrificial protection.

What is oxidation in terms of oxygen?

Gain of oxygen.

What is reduction in terms of oxygen?

Loss of oxygen.

What is oxidation in terms of electrons?

Loss of electrons.

What is reduction in terms of electrons?

Gain of electrons.

What is a redox reaction?

Both oxidation and reduction occur.

What is an oxidising agent?

Causes oxidation by gaining electrons.

What is a reducing agent?

Causes reduction by losing electrons.

What is an ore?

Rock containing metal compounds.

Where are unreactive metals found?

As pure elements.

How is iron extracted?

Reduction with carbon in a blast furnace.

How is aluminium extracted?

By electrolysis of molten aluminium oxide.

Why is electrolysis used for aluminium?

Aluminium is too reactive for carbon reduction.

Why are alloys harder than pure metals?

Different-sized atoms distort layers → harder to slide.

What are the uses of aluminium?

Aircraft, cans (light, corrosion-resistant).

What are the uses of copper?

Wires, pipes (good conductor, malleable).

What are the uses of iron/steel?

Construction (strong); stainless steel for corrosion resistance.

What is the colour of litmus in acid?

Red.

What is the colour of litmus in alkali?

Blue.

What colour does phenolphthalein turn in alkali?

Pink.

What colour does methyl orange turn in acid?

Red.

What do acids release in water?

H⁺ ions.

What do alkalis release in water?

OH⁻ ions.

What is neutralisation?

Acid + alkali → salt + water.

What is a titration used for?

To find exact volumes for neutralisation.

Which compounds are always soluble?

All nitrates; sodium, potassium, ammonium salts.