Difficult IGCSE Chemistry Concepts (memorisation!)

Chemistry Triple IGCSE. Some of these have been stolen.. sorry cillian

prepare a pure, dry insoluble salt from two soluble salts

* Mix and stir two soluble salts
* Filter insoluble salt out
* Wash with deionised water
* Let salt dry

When the salt produced is insoluble, what type of reaction should you do to prepare a pure, dry soluble salt

precipitation

when one reactant is insoluble, what two methods should you use to prepare a pure, dry soluble salt

* filtration
* crystallisation

if both reactants and the sale are soluble, which method should you use to make a salt

titration

prepare a pure, dry sample of magnesium nitrate crystals from magnesium oxide and nitric acid

* Warm acid


* Add magnesium oxide until in excess
* Stir
* Filter to remove excess solid


* Heat filtrate
* Until crystallisation point
* Leave the solution to cool
* Filter solution
* dry crystals in warm oven

magnesium oxide; soluble or insoluble?

soluble

if the cation is in group one or ammonium, is it soluble

yes

if the anion is nitrate, is it soluble?

yes

sodium compounds; soluble or insoluble

soluble

potassium compounds; soluble or insoluble

soluble

ammonium compounds; soluble or insoluble

soluble

nitrate compounds; soluble or insoluble

soluble

chloride compounds; soluble or insoluble

soluble

sulphate compounds; soluble or insoluble

soluble

hydroxide compounds; soluble or insoluble

insoluble

carbonate compounds; soluble or insoluble

insoluble

insoluble chlorides

silver, lead

insoluble sulphates

lead, calcium, barium

soluble carbonates

sodium, potassium, ammonium

soluble hydroxides

sodium, potassium, ammonium, calcium

how to make a salt pure and dry (after filtration)

* Wash with water
* dry between filter papers

why is HCl not used to acidify silver nitrate ions

* it contains chloride ions
* it produces a precipitate with silver nitrate
* it reacts with silver nitrate

colour of phenolphthalein in alkali

pink

colour of phenolphthalein in acid

colourless

colour of methyl orange in alkali

red

colour of methyl orange in acid

yellow

colour of litmus paper in acid

red

colour of litmus paper in alkali

blue

what absorbs phenolphthalein

activated charcoal (then filter to remove)

after obtaining a pure solution from a titration, how should you obtain pure, dry crystals

* Heat the solution to crystallisation point
* Leave the solution to cool and let crystals form
* Filter
* Dry in a warm oven

observations seen when group 2 metal reacts with water

* fizzing
* metal disappears
* test tube feels warm

pure, dry insoluble solid from two soluble solids

* Dissolve. in water
* Mix
* Filter
* Wash precipitate
* drying method

can a combustion reaction occur without oxygen

NO!!!!!!

titration steps (acid to alkali)

* Measure 25 cm3 sodium hydroxide solution into a conical flask using a pipette
* Add a few drops of a suitable indicator to the solution 
* Fill the burette with acid, record the volume 
* Add the acid to the alkali solution until the endpoint
* Record the final volume of acid
* repeat for concordant results

why would you not use a supercolourful substance for a titration?

it masks the colour of the indicator

common impurity in fuels

sulphur

catalyst(s) used in cracking (choose easy marking and pick THREE MINIMUM!)

* Silica
* alumina
* silicon dioxide
* aluminium oxide
* aluminosilicates
* zeolite

temperature of cracking

\:

* 600-700 oC

Incomplete combustion

not enough oxygen gas is present in order to form carbon dioxide and water

how does nitrogen turn into acid rain (combustion engines)

* Nitrogen oxygen react in air
* high temp
* nitrogen oxide(s) created
* Oxides react with water vapour in the atmosphere
* forming nitric acid

particulates

mixture of solid carbon particles and unburnt hydrocarbons

why do long-chain alkanes have a higher boiling point than short-chain alkanes

* larger molecules in a longer chain
* stronger intermolecular forces
* More energy is needed to overcome the forces and separate the molecules

what should you refer to when something has a simple molecular structure and you’re talking about boiling points

overcoming intermolecular forces of attraction

explain the process of fractional distillation

* Crude oil heated
* vapours rise up the column
* column is hotter at the bottom than the top
* Vapours have different boiling points
* Vapours condense at their boiling point

kerosine uses (give 3)

* Aircraft fuel


* paraffin
* heaters

isomers

Compounds with the same molecular formula but different structural and displayed formulae

how to draw isomers

* Draw the carbons 
* Break one carbon off the main chain and place it somewhere else on the main chain
* Add all the hydrogens

what is required for alkanes to react with halogens

UV light

what happens in a free radical substitution reaction

In this reaction, one atom on the alkane is replaced by another in a compound. The leftover two atoms react in most cases.

which enzyme is present in yeast (for fermentation to produce alcohol)

zymase

why is yeast added (for fermentation of alcohol)

* biological catalyst - it is an enzyme
* which increases the rate of reaction

why can fermentation not happen in the presence of air

* Oxygen reacts with ethanol
* ethanoic acid forms

methods of ethanol production

* fermentation (yeast)
* Addition (steam)

conditions needed for steam production of alcohol (ethanol)

* Phosphoric acid
* 300 °C
* 60–70 atm

catalyst needed for steam production of alcohol (ethanol)

phosphoric acid

fuel

a substance which releases thermal energy when undergoing combustion

colour change observed when heating ethanol and acidified potassium dichromate (VI)

orange to green

alcohols will undergo ___________ when heated with oxidising agents…

* oxidation

oxidising agent example (for ethanol)

* Acidified potassium dichromate(VI)

how is potassium dichromate(VI) acidified

* adding dilute sulphuric acid

colour of copper(II) sulfate solution

blue

crystallisation method

* Heat the solution
* Until some water boils off
* Leave the solution to cool
* Filter the crystals
* Dry the crystals

what else could you be asked to do in a crystallisation question

* filter
* saturation
* until crystals form on a cooled sample

ammonium formula

NH4+

ionic bond

* Electrostatic force of attraction
* Between oppositely charged ions