Separate Chemistry II

Potassium ion (K⁺)

Lilac

Sodium ion (Na⁺)

Yellow

Lithium ion (Li⁺)

Red

Calcium ion (Ca²⁺)

Brick red (orange

Copper ion (Cu²⁺)

Blue

Flame test method

Clean nichrome loop with dilute HCl + water → dip in sample → hold in flame → record colour

Test for halide ions

Add dilute nitric acid, then silver nitrate, observe precipitate

Chloride ion (Cl⁻)

White precipitate

Bromide ion (Br⁻)

Cream precipitate

Iodide ion (I⁻)

Yellow precipitate

Test for carbonate ions

Add dilute acid, bubbling shows CO₂ formed

Result for carbonate ions

Bubbling indicates carbonate present

Test for sulfate ions

Add dilute HCl, then BaCl₂ → white precipitate forms

Result for sulfate ions

White precipitate = sulfate present

Aluminium ion (Al³⁺)

White precipitate dissolves in excess → colourless solution

Calcium ion (Ca²⁺)

White precipitate, insoluble in excess

Iron(II) ion (Fe²⁺)

Green precipitate

Iron(III) ion (Fe³⁺)

Brown precipitate

Copper(II) ion (Cu²⁺)

Blue precipitate

Ammonium ion (NH₄⁺)

White precipitate, releases ammonia on warming

Why ion tests must be unique

To identify ions without uncertainty

Hydrogen gas

Lighted splint → squeaky pop

Oxygen gas

Glowing splint → relights

Carbon dioxide

Bubble through limewater → turns milky

Ammonia gas

HCl on glass rod → white smoke (ammonium chloride)

Chlorine gas

Damp litmus paper → bleached

INSTRUMENTAL METHODS

Advantages

Sensitive, accurate, fast, widely available

Flame photometry (concentration)

Use calibration curve to find unknown concentration

Flame photometry (identification)

Compare emission spectra with references

Molecular formula of methane

CH₄

Molecular formula of ethane

C₂H₆

Molecular formula of propane

C₃H₈

Molecular formula of butane

C₄H₁₀

Why alkanes are saturated

Only single C–C bonds

Molecular formula of ethene

C₂H₄

Molecular formula of propene

C₃H₆

Molecular formula of butene

C₄H₈

Why alkenes are unsaturated

Contain C=C double bond

Reaction of ethene with bromine

Ethene + Br₂ → 1,2

Bromine water test

Alkane: stays orange; Alkene: turns colourless

Complete combustion

Hydrocarbon + O₂ → CO₂ + H₂O

Define polymer

Large molecule of repeating units

Define condensation polymer

Two monomers join, releasing small molecule (e.g. H₂O)

Define ester link

Link formed by alcohol + carboxylic acid

Why polyesters are condensation polymers

Dicarboxylic acid + diol → ester link + water

Polymerisation of ethene

→ poly(ethene)

Polymerisation of propene

→ poly(propene)

Polymerisation of chloroethene

→ poly(chloroethene) (PVC)

Polymerisation of tetrafluoroethene

→ poly(tetrafluoroethene) (PTFE)

Deduce monomer from polymer

Identify repeat unit, change single to double bond

Poly(ethene)

Bags, wraps, bottles (cheap, flexible)

Poly(propene)

Buckets, crates, ropes (strong, flexible)

Poly(chloroethene) (PVC)

Pipes, windows, insulation (tough, insulating)

Poly(tetrafluoroethene) (PTFE)

Non

Availability of materials

Low supply = expensive production

Persistence in landfill

Non

Combustion gases

CO₂ and CO (greenhouse and toxic effects)

Sorting polymers

Difficult and costly

Advantages of recycling

Saves resources, reduces landfill, lowers CO₂

Disadvantages of recycling

Costly, energy

DNA

Polymer of nucleotides

Starch

Polymer of sugars

Proteins

Polymer of amino acids

Methanol

CH₃OH

Ethanol

CH₃CH₂OH

Propanol

CH3CH2CH2OH

Butanol

CH3CH2CH2CH2OH

Functional group in alcohols

–OH

Product when dehydrated

Alkene

Oxidation of ethanol

Produces ethanoic acid

Oxidation of methanol

Produces methanoic acid

Oxidation of propanal

Propanoic acid

Oxidation of butan

1

Investigating alcohol combustion

Measure temperature rise and mass loss using 100 cm³ water calorimeter

Methanoic acid

HCOOH

Ethanoic acid

CH₃COOH

Propanoic acid

CH₃CH₂COOH

Butanoic acid

CH₃CH₂CH₂COOH

Functional group

–COOH

Properties

Acidic

Why homologous series react similarly

Same functional group

Fermentation

Sugar + yeast, 15–35 °C, anaerobic → ethanol + CO₂

Fractional distillation

Heat to 78 °C, ethanol vaporises and condenses

Size

1–100 atoms, between atoms and bulk materials

Catalyst use

High surface area → faster reactions

Use in sunscreens

TiO₂ blocks UV, no white residue

Risks

Unknown long

Glass

Transparent, strong, durable, insulator

Clay ceramics

Hard, compression

Polymers

Tough, flexible, poor conductor

Composites

Tailor

Metals

Shiny, ductile, malleable, conductive