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AQA A Level Chemistry > Practical Chemistry > Flashcards

Practical Chemistry Flashcards

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1
Q

when preparing a standard solution, what features should the chemical being used have

A

it should:
- not absorb moisture from or lose moisture to the environment
- have an accurately known relative formula mass so the number of moles dissolved can be determined (e.g. not a hydrated salt)
- be very pure
- have a relatively high relative formula mass so that weighing errors are minimised

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2
Q

what is a standard solution

A

a standard solution is a solution for which the concentration is accurately known

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3
Q

how do you calculate percentage error

A

(uncertainty/quantity measured) x 100

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4
Q

what is the percentage error of 1g if the measurement is to 1 decimal place

A

10%

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5
Q

what is the percentage error of 1g if the measurement is to 2 decimal places

A

1%

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6
Q

what is the uncertainty if the balance is to:
a) one decimal place
b) two decimal places

A

a) +/-0.1g
b+/-0.01g

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7
Q

what is the enthalpy change of combustion

A

the enthalpy change when 1 mole of a substance is burned completely in excess oxygen with all reactants and products in their standard states under standard conditions

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8
Q

how much does 100cm3 of water weigh

A

100g

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9
Q

what is the enthalpy change of neutralisation

A

the enthalpy change when an acid and alkali react to produce 1 mole of water

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9
Q

describe one way to investigate the rate of a precipitation reaction

A

place a piece of paper with a cross underneah the flask where the reaction is taking place and record the time it takes for the precipitate to obscure the cross

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9
Q

what is reflux

A

the continual boiling and condensing of a reaction mixture to ensure the reaction takes place without the contents of the flask boiling dry

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10
Q

why is it often necessary to heat the reactants under reflux for some time when preparing an organic liquid

A

Because the organic reactants contain strong covalent bonds

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11
Q

what are anti-bumping granules

A

small rough pieces of silica or unglazed pottery that are added to the reaction mixture before reflux

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12
Q

what is bumping

A

large bubbles forming at the bottom when a liquid boils and then moving abruptly upwards causing hazardous splashing

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13
Q

why should anti-bumping granules be used in distillation

A

Anti bumping granules must be used for smooth boiling in distillation because if bumping occurs the liquid can splash into the condenser causing an impure product or it could even blow the distillation apparatus apart

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14
Q

what is a risk assessment

A

a judgement of how likely it is that someone might come to harm if a planned action is carried out

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15
Q

list some general safety rules you should carry out during an experiment

A

wear eye protection at all times
take care when handling hot apparatus
ensure there are no naked flames in the lab when using flammable substances
dispose of chemicals as directed, take particular care of disposing organic chemicals

16
Q

what does a good risk assessment include

A

a list of all the hazards and why they are hazardous
a list of all the potential risks relating to what you do in the experiment
suitable control measures you could take that will reduce or prevent the risk

17
Q

what does this sign mean

A

dangerous to the environment

18
Q

what does this sign mean

A

toxic

19
Q

what does this sign mean

A

gas under pressure

20
Q

what does this sign mean

A

corrosive

21
Q

what does this sign mean

A

explosive

22
Q

what does this sign mean

A

flammable

23
Q

what does this sign mean

A

caution (used for less serious health hazards like skin irritation)

24
Q

what does this sign mean

A

oxidising

25
Q

what does this sign mean

A

Longer term health hazards such as carcinogenicity

26
Q

what is sodium hydrogen carbonate used for in solvent extraction

A

to remove acidic impurities in the organic liquid

27
Q

why is pressure released when you shake the separating funnel in solvent extraction

A

because of the build up of carbon dioxide in an acid + carbonate reaction

28
Q

how do you know which layer is the organic layer in solvent extraction

A
  • refer to the density (more dense layer at the bottom)
  • add water and observe which layer increases (aqueous layer)
29
Q

what are immiscible liquids

A

liquids that do not mix and form two layers

30
Q

why is the percentage yield in the preparation of an organic liquid less than 100%

A

theoretical reasons
- side reactions occur so by-products may be produced instead of the expected products
- the reagents used may be impure
- the reaction is incomplete

practical reason
- some product is lost in the purification steps (e.g. in washing, separating in the separating funnel and in transfer between apparatus)
- some product is lost in distillation

31
Q

what colour will acidified potassium or sodium dichromate change when warmed with a reducing agent such as ethanol

A

they are oxidising agents so they will change from orange to green

32
Q

what would you observe when you shake bromine water in a test tube where C=C (alkenes) are present

A

orange solution changes to colourless solution

33
Q

How can you differentiate between primary/secondary alcohol or aldehyde vs. a tertiary alcohol using a test tube experiment

A

warm the samples with acidified potassium dichromate (vi)

  • if there is a primary/secondary alcohol or aldehyde the orange solution will change to green
  • if it is a tertiary alcohol the solution remains orange (it could not be oxidised)
34
Q

How can you use Tollens reagent (ammoniacal silver nitrate) to differentiate between an aldehyde and a ketone

A

warm with the substance:

with an aldehyde you will observe a silver mirror

with a ketone the solution remains colourless

35
Q

How can you use Fehling’s solution to differentiate between an aldehyde and a ketone

A

warm with the substance:
- with an aldehyde you will observe a red precipitate
- with a ketone the solution remains blue

36
Q

you warmed 3 substances with silver nitrate solution in ethanol, one produced a white ppt, one produced a cream ppt, the other produced a yellow ppt. what are the three substances?

A

white ppt: chloroalkane
cream ppt: bromoalkane
yellow ppt: iodoalkane

37
Q

you added sodium carbonate to a substance and you observed effervescence, the gas produced turns colourless limewater to cloudy. name the substance and the gas produced

A

carboxylic acid
carbon dioxide

38
Q

what would you expect to observe if you add sodium carbonate or sodium hydrogen carbonate to carboxylic acid

A

effervescence, the gas produced will turn colourless limewater cloudy

(note that phenol is weakly acidic and can react with bases and metals but it is not acidic enough to react with carbonates)

39
Q

what would you expect if you add magnesium to carboxylic acid

what gas is produced and how would you test it

A

effervescence

hydrogen - a pop is heard when a lighted splint is applied to the gas produced

40
Q

what can you deduce if you warm a substance with ethanol and a few drops of conc. sulphuric acid and a sweet smell is noticeable

A

an ester has been produced - the organic compound could be a carboxylic acid

AQA A Level Chemistry (2 decks)

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