Organic Practicals

Question 1

Compare the rates of hydrolysis of 1- chlorobutane ,1-bromobutane and 1-iodobutane what would appear first

Answer 1

Silver iodide then silver bromide formed and then silver chloride formed

Due to bond strength C-I is weaker then an C-Br and and then C-cl is weaker

Question 2

What is reagent used for hydrolysis of halogenoalkanes

Answer 2

Aqueous silver nitrate

The leaving group combines with silver nitrate

Question 3

What is the precipitate formed for the halogen hydrolysis reactions

Answer 3

Silver halide precipitate

Question 4

Give additional reagent to form carboxylic acid

Answer 4

Dilute sulfuric acid

Question 5

What is the role of anti bumping granules

Answer 5

To prevent large bubbles

Question 6

How do you test the difference between carboxylic acid and alcohol

Answer 6

Add sodium carbonate

Effervescence bubbles produced

Question 7

When substance is heated in reflux ,how must the condenser appear

Answer 7

Never sealed
Condenser must have two openings for water in and out

Question 8

Why is sodium carbonate added when forming an ester and why there is build up in pressure

Answer 8

To neutralise

CO2 is produced

Question 9

How are esters hydrolysed

Answer 9

Under reflux
Using dilute HCL

Question 10

Describe the formation of ester practical

Answer 10

Propane acid and ethanol mixed to round bottom flask

Concentrated sulfuric acid added

When acid has been added, reflux condenser is fitted to the flask and heated with electric heating mantle

The mixture is cooled and rearranged for distillation

Distillate placed in separating funnel and shaken

Ester is run into dry flask containing anhydrous calcium chloride

Filters with anti bumping granules

Question 11

Why is electric heater used for formation of ester

Answer 11

Controls heating because it can be extremely flammable

Question 12

Why is calcium chloride used in formation of ester

Answer 12

It is a drying agent

Question 13

describe the distillation of primary alcohol

Answer 13

Place dilute sulfuric acid in a flask and add potassium dichromate(VI) and 2 or 3 anti- bumping granules.

-Shake the contents of the flask until solution is complete (do not warm).
- Add propan-1-ol in drops from a dropping pipette, shaking the flask so as to mix the contents, and then assemble distillation apparatus as shown below
- Gently heat and slowly distil liquid into a test tube, taking care that none of the reaction mixture splashes over.

Question 14

what is the group test for alkene and result

Answer 14

bromine water in a test tube add a few drops of the unknown and shake.

Observation: alkenes should decolourise bromine water

Question 15

how is tollens reagent formed

Answer 15

Reagent: Tollens’ reagent formed by mixing aqueous ammonia and silver
nitrate. The active substance is the complex ion of [Ag(NH3)2]+

Question 16

what is the test for aldehyde using tollens reagent

Answer 16

Conditions: heat gently
Reaction: aldehydes only are oxidised by Tollens’ reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms
Observation: with aldehydes, a silver mirror forms coating the inside of the
test tube. Ketones result in no change.

Question 17

describe the test for aldehydes using fehlings

Answer 17

Reagent: Fehling’s solution containing blue Cu 2+ ions.
Conditions: heat gently
Reaction: aldehydes only are oxidised by Fehling’s Solution
into a carboxylic acid. The copper (II) ions are reduced
to copper(I) oxide .
Observation: Aldehydes: Blue Cu 2+ ions in solution change
to a red precipitate of Cu2O. Ketones do not react

Question 18

how do you test for the presence of carboxylic acid

Answer 18

The presence of a carboxylic acid can be tested by
addition of sodium carbonate. It will fizz and produce
carbon dioxide.

Question 19

what reagent is used in the test for alcohol

Answer 19

potassium dichromate and sulfuric acid

Question 20

what is the test of chloroalkane

Answer 20

warm with silver nitrate
formation of white precipitate of AgCl

Question 21

what is aspirin made of

Answer 21

Aspirin is made from 2-hydroxybenzoic acid which contains a phenol group.

In the reaction the phenol group is turned into an
ester by reacting it with the reactive ethanoic anhydride

Question 22

what type of reaction is the formation of aspirin

Answer 22

esterification

Question 23

how are insoluble impurities removed

Answer 23

Hot filter solution through (fluted) filter paper quickly.

Question 24

how do you test for the degree of accuracy

Answer 24

One way of testing for the degree of purity is to determine the melting
“point”,

Question 25

how is the melting point lowered

Answer 25

If impurities are present (and this can include solvent from the recrystallisation process) the melting point will be lowered and the sample will melt over a range of several degrees Celsius

Question 26

how is melting point measured

Answer 26

Melting point can be measured in an electronic melting point machine

Question 27

describe the practical for thin layer chromatography

Answer 27

1.draw a pencil line 1 cm above the bottom of a TLC plate and mark spots for each sample, equally spaced along line. 2) Use a capillary tube to add a tiny drop of each solution to a different spot and allow the plate to air dry. 3) Add solvent to a chamber or large beaker with a lid 4) Place the TLC plate into the chamber, making sure that the level of the solvent is below the pencil line. Replace the lid to get a tight seal. 5) When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil. Allow the plate to dry in the fume cupboard. f) Place the plate under a UV lamp in order to see the spots. Draw around them lightly in pencil. g) Calculate the Rf values of the observed spots.

Question 28

why do we draw a pencil line

Answer 28

pencil line –will not dissolve in the solvent

Question 29

why do we use a tiny spot on the line

Answer 29

too big a drop will cause different spots to merge

Question 30

why is a lid used

Answer 30

lid– to prevent evaporation of toxic solvent

Question 31

why is dryed in a fume cupboard

Answer 31

dry in a fume cupboard as the solvent is toxic

Question 32

what is the rf value

Answer 32

Rf value = distance moved by amino acid divided by distance moved by the solvent

Question 33

what does the seperation of chromatography depend on

Answer 33

Separation by chromatography depends on the balance between solubility in the moving phase and retention in the stationary phase.

Question 34

For oxidation of secondary alcohol how is the apparatus meant to be set up

Answer 34

Needs to have anti bumping granules To create smaller bubbles System should be closed Stops gases from escaping since it’s volatile Water should be flowing the right direction Water should be going in at the furthest end of the condenser

Question 35

What technique is used to separate propane acid from reaction mixture

Answer 35

Fractional distillation

Question 36

In the formation of cyclohexene why is sodium chloride added

Answer 36

Help separate the organic layer from the aqueous layer

Question 37

In the formation of cyclohexane why is anhydrous calcium chloride added

Answer 37

It is insoluble in cyclohexene Acts as a drying agent