IGCSE Chemistry

markscheme answers and keywords

characteristics of compounds in a homologous series

• same general formula

• same functional group

• trend/gradual change in physical habits

• similar chemical properties

• neighbouring members differ by same stated increments

exothermic

= a reaction which releases thermal energy to surroundings

condenser in distillation

M1: condenser cools ethanol vapour

M2: ethanol vapour condenses into a liquid

alkaline metal + water

• effervescence

• floats

• moves

• white trail

• gets smaller

phenolphthalein

• colourless in acidic/neutral

• pink in alkalis because OH-/ hydroxide ions are present

reason for cleaning wire before flame test

• prevent impurities that will affect results

• so they don’t interfere with flame colour

percentage of nitrogen in atmosphere

78%

environmental effects of acid rain

• acidifies lakes

• kills fish

test for ammonium

M1: add sodium hydroxide and heat

M2: test gas with red litmus paper

M3: red litmus turns blue

isomers

M1: compounds with the same molecular formula

M2: but different structural/displayed formula

methods for disposing polymers

• burying them in landfill sites

  • inert/unreactive/do not biodegrade

• burning them to release heat energy

  • produce toxic fumes/greenhouse gases when burned

carbon monoxide effect

• poisonous

• toxic

• limits capacity to carry oxygen in blood

purpose of cotton wool

to prevent acid spray from leaving flask

percentage yield

(actual yield/ theoretical yield) * 100

silver ion

Ag⁺

copper ion

Cu²⁺

iron ion

Fe²⁺ and Fe³⁺

lead

Pb²⁺

zinc

Zn²⁺

hydroxide

OH^-

hydrogen

H⁺

ammonium

NH₄⁺

carbonate

CO₃^2-

nitrate

NO₃^-

sulfate

SO₄^2-

covalent bond

= electrostatic attraction between atoms by the sharing of a pair of electrons

solubility rules

• common sodium, potassium and ammonium compounds are soluble

• all nitrates are soluble

• common chlorides are soluble - except silver and lead(II)

• common sulfates are soluble - except barium, calcium and lead(II)

• common carbonates are insoluble - except sodium, potassium and ammonium

• common hydroxides are insoluble - except sodium, potassium and calcium (slight soluble)

acid

proton donor

base

proton acceptor

catalyst

lower the activation energy by providing an alternative pathway

properties of alkanes

• shorter alkanes are more volatile & more flammable

• the longer the chain the higher the boiling point

describe how crude oil is separated into fractions in the fractionating column [4 marks]

M1: crude oil is heated from liquid to gas/vapourized

M2: column is hotter at the bottom and cooler at the top

M3: vapours/gases rise up the column

M4: vapours condense at their boiling point

bitumen uses

• road tar

• surfacing roads

cracking

= process of breaking down long-chain hydrocarbons to form shorter chains of alkanes/alkenes/hydrocarbons

unsaturated hydrocarbons

• double bond between carbon atoms

• contains only hydrogen and carbon atoms

explain why metals are malleable

• layers of metal cations

• can slide over each other

negative elctrode

• place of reduction (gain of electrons)

• negatively charged so it attracts cations

why sodium metal doesn’t form in the electrolysis of an aqueous solution of sodium chloride

= sodium is more reactive than hydrogen

dynamic equilibrium

• forwards and reverse reactions occur at the same rate

• concentrations of reactants and products remain constant

titration

• rinse burette with named alkali

• fill burette with named alkali

• make sure that jet contains liquid

• add a few drops of indicator to conical flask

• add named alkali from the burette until indicator changes colour permanently

• swirl the conical flask

• near the end-point add dropwise

• record the final and initial volume on burette

• repeat until concordant results

exothermic reaction reasoning

• energy released from bond formation is greater than energy absorbed for bond breaking

• bond formation is exothermic/ bond breaking is endothermic

faraday

= a unit of electric charge; amount of electric charge needed to supply one mole of electrons.

• equivalent to 96 500C (Coulombs)

sulfur dioxide + water

sulfurous acid

pollutants thar form acid rain

• nitrogen oxide

• sulfur dioxide

problems caused by acid rain

• corrodes limestone

• causes iron to rust

• harms aquatic life

what happens to temperature change when the volume of the solvent is increased

• change in temperature is less

• because a larger volume has to be heated