organic chemistry practical mistakes

Differences between reflux and distillation

• distillation separates chemicals / products from mixture

• Reflux keeps all chemicals inside of reaction vessel

How to purify a solid / recrystallisation (5)

1. Add just enough hot solvent, that solute isn’t soluble in at rtp, to solid, to form saturated solution

2. Filter hot solution to remove impurities, using gravity filtration

3. Leave filtered sample to cool

4. Sample crystalises, and impurities stay in solution, because their concentration is much lower

5. Crystals removed by filtration and washed in ice cold solvent

How to purify liquid

1. shake (invert) and leave in separating funnel

2. tap off aqueous layer and collect (usually bottom layer) organic product

3. dry with anhydrous salt eg Ca2Cl

4. Redistill and refraction at boiling point of product

Using TLC to monitor course of reaction

Take samples at regular intervals from reaction and run on TLC plate with reactants (and product)

Confirm identity of aldehyde / ketone using 1 test

Add 2-4 DNPH

Orange precipitate = aldehyde or ketone

Filter out and recrystallise precipitate

Melt and compare melting points to known / library values

Why is phenol more easier to nitrate than benzoic acid

Lone pair in O of alcohol is partially donated to delocalised pi electron system

Increasing electron density in the ring / making the ring more susceptible to electrophillic attack

COOH is an electron withdrawing group

Reduction of nitrobenzene to phenyl amine conditions

Sn / concentration HCl

How to turn carboxylate to carboxylic acid

H+ from acid protonates with carboxylate to form carboxylic acid

How to use neutralising agent in purifying liquid and example

1. when an acid catalyst is used

2. after separating funnel, use neutralising agent on organic layer

3. eg sodium carbonate

Draw the apparatus for filtration under reduced pressure / vacuum filtration (2)

Ways waste polymers can be disposed usefully (2)

• Combusted to generate energy / electricity

• used as chemical / organic feedstock

• recycling

butanol to butanoic acid equation (2)

CH3CH2CH2CHOH + 2[O] → CH3CH2CH2COOH + H2O

Why don’t we use a beaker, stand, and bunsen burner to oxidise butanol to butanone, and what else could we use? (2)

alcohol is flammable / will evaporate away

heat under reflux with pear shaped flask instead

type of reaction of alcohol to alkene (1)

dehydratoin / elimination

Tests for carboxylic acids (3)

Reactive metal: H2 gas / fizzing

Metal carbonate / CO2 / fizzing

Universal indicator: pH of weak acid

Do you use neutralising agent before or after the seperating funnel

After

How can the purity of a solid be checked

Melt a sample and compare melting point to known / database values

A reaction in aqueous solution forms a salt that is soluble in water. How to form and separate the acid that is soluble in water

Add acid and then use separating funnel

How to purify a liquid acid

Distillation

How to check aqeuous vs organic layer

Add water. Layer that increases in volume is organic layere

Name all parts of distillation apparatus (6)

• thermometer

• anti bumping granules

• pear bottomed / shaped flask

• still head

• condenser

• receiver / beaker

Which way does water flow in distillation

Water comes out nearer the flask, from the top of the condenser

Water enters nearer the receiver, on the bottom of the condenser

Quick test for Aldehyde

Add Tollens reagent and heat

Silver mirror precipitate: aldehyde

What test for haloalkane also identifies the hallide with colours

Add AgNO3 (aq) and ethanol as the solvent

White ppt: cl, cream: br, yellow: I

If the organic layer’s density is less than 1 g per cm, is it on top or bottom layer of seperating funnel

less dense than water, so top