Praticals

Question 1

Test for water formation?

Answer 1

Add water sample to anhydrous copper sulfate and it turns from white to blue

Question 2

What observations are made when a carbonate is heated?

Answer 2

Black solid is formed

Steamy fumes are produced

Question 3

How do you do the iodoform test ?

Answer 3

Add NaOH (aq) to Iodine solution and heat in water bath

Question 4

Why are the components of nitrating mixture are pre cooled and mixed very slowly?

Answer 4

The reaction is very exothermic

Question 5

Why is the nitration reaction always at or below room temperature?

Answer 5

To prevent multiple substitution of nitro groups

Question 6

Distillation value for 1-methyl-2-nitrobenzene

Answer 6

218-221 degree celsuis

Question 7

Suggest the best way to obtain some pure 1-methyl-2,4-dinitrobenzene after the distillation.

Answer 7

further distillation and recrystillation

Question 8

Method for recrystallisation?

Answer 8

1. add a min vol of hot solvent
2. hot filter sol through fluted filter paper
3. cool down filtrate to allow crystals to form (using ice bath)
4. suction filter filtrate through Buchnner vacuum filter
5. add cold solvent to wash crystals
6. dry crystals between absorbent paper

Question 9

Suitable drying agents?

Answer 9

CaCl2, MgSO4, Na2So4

Question 10

Observations when using a drying agent?

Answer 10

It will go from powdery to crystallising. If it stops crystallising, reaction is done
You can then filter it off

Question 11

What is washing?

Answer 11

Removing impurities from a solid or liquid using water or an inorganic solvent

Question 12

What is steam distillation?

Answer 12

Separates insoluble substances from aqueous solution by adding steam to cause agitations on the surface of mixture

Question 13

Advantage of steam distillation?

Answer 13

Insoluble substance is distilled off at a low temperature- it prevents decomposition

Question 14

Method of solvent extraction

Answer 14

1. add reaction mixture and then add solvent
2. SHAKE APPARATUS TO MIX
3. open the stopper to RELEASE PRESSURE
4. once two layers have formed, open the tap and decant first layer (if wanted put into a beaker)

Question 15

Why should you add the solvent for solvent extraction in small samples

Answer 15

removes less of the desired product

Question 16

safety conditions to consider when heating under reflux ?

Answer 16

1. Add anti bumping granules so the boiling is even
2. water should enter in from the bottom and leave from the top for efficient cooling
3. Nothing is blocking the top of condenser-increase pressure inside condenser
4. Thermometer is inline with the lines of the condenser as we are measuring the temperature of vapours

Question 17

What are the features of a solvent used in solvent extraction?

Answer 17

Must be immiscible in the reaction mixture

Organic layer must be more soluble in solvent than in reaction mixture

Question 18

How do impurities affect melting point?

Answer 18

They decrease the melting point and there’s no longer a sharp value

Question 19

How do impurities affecting boiling point?

Answer 19

They increase the boiling point and theres no longer a sharp boiling point

Question 20

How to determine melting point? (apparatus and method)

Answer 20

Place thermometer attached to a capillary tube with solid sample attached to it inside of melting point apparatus
The oil inside of the apparatus needs to have a higher boiling point than samples melting point and needs to be low flammability
Then you compare value with data booklet values

Question 21

What is the purpose of simple distillation?

Answer 21

Used for purification and separating two substances with different boiling temps

Question 22

Disadvantage of simple distillation?

Answer 22

Substances need to have a large difference in point

Question 23

Advantage of simple distillation?

Answer 23

Easier and quicker to set up

Question 24

What do you add to fractionating column and what’s the purpose ?

Answer 24

You add pieces of broken glass or glass beads to act as a surface for which the vapour can condense onto

Question 25

When should you use fractional distillation?

Answer 25

When you have several substances to separate that do not have a large diff in boiling temp

Question 26

Why is a pipette rinsed with standard solution and not water?

Answer 26

The standard solution removes any containments | Adding water would dilute the solution/decrease the concentration

Question 27

Why is the actual yield usually lower than theoretical yield?

Answer 27

Side reactions occur Reaction was incomplete Products are lost in purification Products are lost in transfer

Question 28

How do you make a sample of at least 100cm^3 of 0.1moldm-3 of something with a sample of 1.0 moldm-3

Answer 28

Using a pipette of at 10cm3 from your 1moldm3 sample. Place this sample in a volumetric flask Make up sample to 100cm3 using distilled water and invert

Question 29

Test for phenol group?

Answer 29

Forms a white ppt with Br2 (aq)

Question 30

Method of steam distillation

Answer 30

steam is passed into the mixture | product vapour is distilled off with the water

Question 31

Test for OH group and observations

Answer 31

Add Na- fizzing/effervescence and white ppt forms or Add PCl5- causes misty fumes

Question 32

Indicator used in I2 + thiosulphate reactions

Answer 32

starch | goes from blue-black to colourless

Question 33

why is a desiccator used?

Answer 33

to prevent decomposition

Question 34

why happens if there is an air bubble in the burette?

Answer 34

Some reagent is used to fill the jet | which leads to an increased titre

Question 35

how to crystallise something?

Answer 35

evaporate solution to crystallisation point | place crystals in a desiccator to dry

Question 36

what is a measuring cylinder used for?

Answer 36

measuring greater volumes easier | can be used for multiple experiments

Question 37

what is a burette used for?

Answer 37

allows for precise measurement

Question 38

how to make sure the results of a titration are more reliable?

Answer 38

by splitting sample into two and repeating the titration

Question 39

biggest source of error with formation of metal salt with a carbonate experiment

Answer 39

some Co2 dissolves in HCl

Question 40

what's the purpose of calculating a rough titre?

Answer 40

gives an indication to when you are supposed to be adding drop by drop

Question 41

how does refluxing work?

Answer 41

cold water passes through the condenser and condenses vapours that form and prevents the escape of reactants and products

Question 42

temperature range of carboxylic acid

Answer 42

200-204 degrees celsius

Question 43

whats the purpose of adding a thermometer to distillation equipment

Answer 43

to prevent the escape of reagents | and to measure the temperature of vapours

Question 44

what's the purpose of making washes and what happens if you don't

Answer 44

If you don't less of the reagents is present so less product is produced

Question 45

what is the effect if during a titration missed the end point?

Answer 45

more of the reagent would show greater amount of the product