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A- Level Chemistry > Praticals > Flashcards

Praticals Flashcards

1
Q

Test for water formation?

A

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

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2
Q

What observations are made when a carbonate is heated?

A

Black solid is formed

Steamy fumes are produced

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3
Q

How do you do the iodoform test ?

A

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

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4
Q

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

A

The reaction is very exothermic

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5
Q

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

A

To prevent multiple substitution of nitro groups

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6
Q

Distillation value for 1-methyl-2-nitrobenzene

A

218-221 degree celsuis

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7
Q

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

A

further distillation and recrystillation

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8
Q

Method for recrystallisation?

A
  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
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9
Q

Suitable drying agents?

A

CaCl2, MgSO4, Na2So4

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10
Q

Observations when using a drying agent?

A

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

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11
Q

What is washing?

A

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

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12
Q

What is steam distillation?

A

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

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13
Q

Advantage of steam distillation?

A

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

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14
Q

Method of solvent extraction

A
  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)
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15
Q

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

A

removes less of the desired product

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16
Q

safety conditions to consider when heating under reflux ?

A
  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
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17
Q

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

A

Must be immiscible in the reaction mixture

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

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18
Q

How do impurities affect melting point?

A

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

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19
Q

How do impurities affecting boiling point?

A

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

20
Q

How to determine melting point? (apparatus and method)

A

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

21
Q

What is the purpose of simple distillation?

A

Used for purification and separating two substances with different boiling temps

22
Q

Disadvantage of simple distillation?

A

Substances need to have a large difference in point

23
Q

Advantage of simple distillation?

A

Easier and quicker to set up

24
Q

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

A

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

25
Q

When should you use fractional distillation?

A

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

26
Q

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

A

The standard solution removes any containments

Adding water would dilute the solution/decrease the concentration

27
Q

Why is the actual yield usually lower than theoretical yield?

A

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

28
Q

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

A

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

29
Q

Test for phenol group?

A

Forms a white ppt with Br2 (aq)

30
Q

Method of steam distillation

A

steam is passed into the mixture

product vapour is distilled off with the water

31
Q

Test for OH group and observations

A

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

32
Q

Indicator used in I2 + thiosulphate reactions

A

starch

goes from blue-black to colourless

33
Q

why is a desiccator used?

A

to prevent decomposition

34
Q

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

A

Some reagent is used to fill the jet

which leads to an increased titre

35
Q

how to crystallise something?

A

evaporate solution to crystallisation point

place crystals in a desiccator to dry

36
Q

what is a measuring cylinder used for?

A

measuring greater volumes easier

can be used for multiple experiments

37
Q

what is a burette used for?

A

allows for precise measurement

38
Q

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

A

by splitting sample into two and repeating the titration

39
Q

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

A

some Co2 dissolves in HCl

40
Q

what’s the purpose of calculating a rough titre?

A

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

41
Q

how does refluxing work?

A

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

42
Q

temperature range of carboxylic acid

A

200-204 degrees celsius

43
Q

whats the purpose of adding a thermometer to distillation equipment

A

to prevent the escape of reagents

and to measure the temperature of vapours

44
Q

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

A

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

45
Q

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

A

more of the reagent would show greater amount of the product

A- Level Chemistry (13 decks)

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