U2 Chem

Observations from combustion of alcohols

Blue flame (complete combustion), less clean the longer the chain

Observations from the oxidation of an alcohol using KCr2O7

The reaction mixture turns from orange to green

Conditions for oxidation of alcohols

Oxidising agent like KCr2O7, dilute H2SO4, heat under reflux/ distillation with addition

What oxidation reactions do alcohols undergo

• 1* alcohols → aldehyde (and water) → carboxylic acid

• 2* alcohols —> ketone

• 3* alcohols —> no reaction

Conditions for the dehydration of alcohols

Concentrated acid -phosphoric acid and heat

Conditions for the chlorination of a 1* or 2* alcohol

PCl5 (white solid)

Conditions for the chlorination of a 3* alcohol

Concentrated HCl and shaking

Conditions for the bromination of an alcohol

Potassium Bromide and sulfuric acid at 50%

Conditions for the iodination for alcohols

Red phosphorous and iodine

Test for a hydroxyl group

PCl5, if the mixture releases misty fumes, a chlorination reaction has taken pace

Test for aldehydes after distilling it from oxidising an alcohol

Benedict’s/ Fehling’s solution (blue —> orange)

Test for carboxylic acids

Base (NaCO3 or NaHCO3) reacts to form CO2 which can be bubbled through lime water and should turn cloudy

Addition reaction general equation

A + B = C

General elimination reaction

• 2 atoms/ groups attached to carbons are removed

• The carbons forms a double bond

Substitution reaction general equation

A + B = C + D

What is a hydrolysis reaction

A type of substitution reaction where the OH replaces an atom/ group

Reaction of hallogenoalkanes with water or alkalis

An alcohol is produced

Mechanism of hallogenoalkane with ethanolic potassium hydroxide

Conditions for the elimination reaction of a hallogenoalkane with an OH- group

Ethanolic KOH with hear under reflux

Test for C-Hallogen bond length and strength

• Hydrolysis reaction: water and heat/ NaOH is added to displace the halide ions

• AgNO3 is added to form a silver halide precipitate

Silver halide precipitate colours

Silver chloride: White

Silver bromide: Cream

Silver iodide: Yellow

Bond test speed for Cl, Br, I and 1*, 2*, 3* hallogenoalkanes from fastest to slowest

I, Br , Cl and 3*, 2*, 1*

Conditions for nucleophilic substitution of ammonia with a hallogenoalkane

• concentrated alcoholic ammonia

• Sealed test tube (pressure)

• Heat

Mechanism for reaction of ammonia with halogenoalkane

(Chlorine may also take a hydrogen to form HCl instead of ammonia in the intermediate)

Reaction mechanism for cyanide ion with hallogenoalkane

Conditions for reaction of cyanide ion with hallogenoalkane

• KCN

• Heat under reflux

Pattern in oxidising and reducing powers of halogens

• Oxidising: high and decreases down the group

• Reducing: low and increases down the group

Colours of halogens in solutions

Chlorine: Pale green

Bromine: Yellow/ orange

Iodine: Brown

Colours of halogens in non polar/ organic solutions

Bromine is a brighter orange and iodine is purple

Cyanide ion

CN-

Colours of halogens in standard conditions

• Fluorine: yellow gas.

• Chlorine: pale green gas.

• Bromine: orange-brown liquid

• Iodine: grey-black solid with purple vapour.

Test for halide ions

-Nitric acid is added to remove other ions like carbonates

-Silver nitrate solution is added

-Once the precipitates are formed if they are difficult to differentiate, NH3(aq) is added to test solubility

Solubility of silver precipitates in aqueous ammonia

• Silver chloride dissolves in dilute concentrations

• Silver bromide dissolves in concentrated concentrations

• Silver iodide does not dissolve

Colours of halides in gases, aqueous solutions or acids

Colourless in all

Rules in oxidation number for oxygen

• Usually 2-

• With flourine it is 1-

• In peroxide it is 1-

Rules in oxidation number for hydrogen

1+ except when combined with a less electronegative element (metals)