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Chemisty A level > Practical Chemistry > Flashcards

Practical Chemistry Flashcards

1
Q

What is a standard solution?

A

a solution whose conc is accurately known

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2
Q

What is a titre?

A

the required volume delivered from the burette

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3
Q

What is the nearest measurement a burette reads to?

A

0.05cm3

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4
Q

How do you ensure all water is removed from a thermal decomp expt?

A

heat to a constant mass

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5
Q

Why is a reful reaction used?

A

allows prolonged heating without loosing material through evapouration

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6
Q

What is an advantage of using a water bath rather than a bunsen burner?

A

better control - heating at a constant temp can be acheived

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7
Q

What are distillations used for?

A

used to purify organic liquids based on different BP

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8
Q

How do you test for Br2?

A

alkenes and phenols will decolourise Br2

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9
Q

What colour are phenols when universal indicator is added?

A

red- orange

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10
Q

What happens when you add sodium carbonate to a phenol and a carboxylic acid?

A

carboxyl = fizzes
phenol= nothing

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11
Q

What happens when you add warm tollen’s reagent to aldehydes?

A

aldehyde gives a silver mirror

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12
Q

What happens when you add warm acidic potassium dichromate to alcohols and aldehydes?

A

solution turns from orange to green

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13
Q

What are the 2 methods you can use to determine the amount of moles?

A

measuring gas collected
measuring mass

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14
Q

How do you produce a standard solution?

A
  1. weigh specific amount of solute into a weighing boat then transfer to 250ml beaker
  2. add small vol of distilled water to the beaker and stir until the solid completely dissolves
  3. transfer solution to a 250ml volumetric flask using a funnel
  4. rinse beaker and glass rod with distilled water into the volumetric flask
  5. fill the volumetric flask up to the graduted line using distilled water
  6. insert a bung and invert several times
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15
Q

What indicator is used for titrations?

A

methyl orange

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16
Q

What is the colour change of methyl orange in titrations?

A

yellow to orange = neutralised

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17
Q

What are the errors of titrations?

A
  • some of the weighed solid may not be transferred from the weighing boat
  • do not spill soild/ solution
  • not swirling = higher titre than expected
  • colour change is not clearly visible
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18
Q

How do you determine the enthalpy change of neutralisation styrofoam cup prac?

A
  1. measure equal volumes of acid and base
  2. record the initial temp of acid in styrofoam cup
  3. add base and record temp at regular intervals for 10 mins
  4. stir the solution each interval
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19
Q

Describe the test for halide ions

A

add dilute nitric acid with carbonate ions so no Ag2CO3 (white solid) forms
add silver nitrate and precipitate forms

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20
Q

How can you test for the presence of Magnesium?

A

add sulfate solution = mg is the only g2 element that is soluble

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21
Q

How can you test for barium?

A

add chromate solution
barium is the only g2 metal that is insoluble

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22
Q

What type of reaction is a haloalkane formed from an alcohol?

A

nucleophilic sub

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23
Q

What are the 3 main stages of sythesising a haloalkane from an alcohol?

A
  1. preparation
  2. separation
  3. distillation
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24
Q

Why do 2 layers form in the separating funnel when synthesising a haloalkane from an alcohol>

A

the aq layer and organic layer have different denisties and they are immiscible (do not mix)

25
Q

What is the purpose of anti-bumping granules?

A

prevents the formation of large gas bubbles that cause violent boiling

26
Q

Why is a base added to an organic layer after synthesing it from an alcohol?

A

to react with any hydrogen-halide remaining

27
Q

Why is a base added to an organic layer after synthesing it from an alcohol?

A

to remove any hydrogen-halide remaining

28
Q

Why do you need to open the stopper on the separating funnel regulary?

A

release build up of pressure and reduce risk of appartus breaking

29
Q

What can you use to heat flammable reactants instead of a bunsen burner?

A

water bath or electric heater

30
Q

What happens during preparation of synthesis of a haloalkane from an alcohol?

A

add alcohol and hydrogen-halide into a separating funnel
place stopper on separating funnel and shake vigorously for 20 mins - release pressure when required

31
Q

How do you separate organic layer from aq layer in a separating funnel?

A

open and close the tap to collect the bottom aq layer
add a base like sodium hydrogen carbonate to separating funnel
shake and release pressure
allow mixture to separate
remove bottom aq layer
repeat until no pressure build up

collect organic layer
add anhydrous MgSO4 and swirl until stops clumping
filter into a round bottom flask

32
Q

How is cyclohexene formed from cyclohexanol?

A

dehydration
1. reflux
2. distillation

33
Q

What is the catalyst for dehydration of alcohols?

A

phosphoric acid

34
Q

What apparatus is used to purify cyclohexene?

A

distillation

35
Q

Why is anhydrous calcium chloride added to any mixture?

A

remove any traces of water

36
Q

What catalyst is used to add a substituent to a benzene ring?

A

sulfuric acid

37
Q

Describe filteration of an organic solid

A
  1. place a piece of filter paper in a buckner funnel
  2. place the funnel in a buchner flask. connect the side arm of the flask to a water pump
  3. connect the water pump to a tap and turn the tap on to create a vacuum. Pour the solution into the funnel
  4. once the solution has drained through, rinse the soild on the filter paper with a small volume of solvent
38
Q

Describe the process of recrystallisation

A
  1. dissolve the solid in the minimum volume of hot solvent
  2. filter to remove insoluble impurities
  3. cool the filtrate
  4. filter to remove soluble impurities
  5. product remains on filter paper
39
Q

Why is product of recrystallisation dissolved in a minimum amount of solvent?

A

if there is a large volume of solvent when the mixture is cooled, some of the product may remain in solution

40
Q

How does recrytallisation improve the purity of a product?

A

desired product is dissolved in an appropriate solvent that impurities are insoluble in
filtration leaves insoluble impurities on the filter paper

41
Q

Why the solution cooled in ice immediately after recrystallisation?

A

to decrease solubility of product so that it crystallises

42
Q

Why must crystals be completely dry before measuring their mass?

A

excess solvent on crystals could falsely increase the yield

43
Q

Why might % yield not be 100% after recrystallisation?

A

product may be lost when filtering or transferring between apparatus
some product may stay in solution after recrystallisation
other side reactions may occur

44
Q

How can you investigate the purity of a product?

A

thin layer chromatography

45
Q

During chromatography, why is a clear watch glass placed on the beaker and TLC plate?

A

prevent evapouration of solvent
should be clear to allow the plate to be monitored

46
Q

In chromatography, what is the solvent front?

A

the furthest distance travelled by the solvent up the TLC plate

47
Q

How do you calc a Rf value?

A

Rf = distance travelled by substance/ distance travelled by solvent

48
Q

How can the purity of a sample be assessed using melting points?

A

pure = has specific MP
impure = range of MP

49
Q

How can the purity of a sample be assessed using melting points?

A

pure = has specific MP
impure = range of MP
smaller range - more pure

50
Q

What is observed from a reaction of an alkane with bromine water?

A

stays orange

51
Q

What is observed from a reaction of a cycloalkane with bromine water?

A

two separate layers form
top layer = orange
bottom layer = water

52
Q

Do alkenes react with bromine water?

A

yes

53
Q

What is observed from a reaction of an alkene with bromine water?

A

orange —> colourless

54
Q

How do you test for haloalkanes?

A
  1. heat the sample with a solution of sodium hydroxide under reflux to release halide ions
  2. add dilture nitric acid
  3. add silver nitrate and observe precipitate formed
55
Q

What is the solubility of AgCl in ammonia?

A

soluble in dilute and conc ammonia

56
Q

What is the solubility of AgBr in ammonia?

A

soluble in conc ammonia

57
Q

What is the solubility of AgI in ammonia?

A

insoluble in ammonia

58
Q

How do you test for carboxylic acids?

A

add sodium carbonate
effervesence - CO2 produced = carboxylic produced
test for CO2 with limewater

59
Q

How do you test for phenol?

A

add bromine water = decolourises

Chemisty A level (28 decks)

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