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GCSE > 4.6 CHEMICAL TESTS > Flashcards

4.6 CHEMICAL TESTS Flashcards

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1
Q

How to carry out a test for hydrogen

A
  • Collect a sample of gas in a test tube
  • Attempt to ignite the gas with a lit splint
  • You will hear a squeaky pop
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2
Q

How to carry out a test for hydrogen

A
  • Collect a sample of gas in a test tube
  • Attempt to ignite the gas with a lit splint
  • You will hear a squeaky pop
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3
Q

What is the chemical reaction when testing hydrogen

A

Combustion - hydrogen forming water

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4
Q

How to test for oxygen

A
  • Collect a sample of gas in a test tube
  • Place a glowing splint in the test tube
  • The splint will relight
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5
Q

What is the chemical reaction taking place when testing for oxygen

A

Combustion of the wood - Pure O2 is more concentrated that the O2 in normal air (splint combusts faster)

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6
Q

How to test for the presnece of water

A
  • Add anhydrous copper (II) sulfate to water
  • Will turn from white to blue
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7
Q

How to test the purity of water

A
  • Measure the boiling point
  • Closer to 100c = more pure
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8
Q

How to test for CO2

A
  • Bubble a sample of gas through limewater
  • A white precipitate forms (goes cloudy)
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9
Q

How to test for CO2

A
  • Bubble a sample of gas through limewater
  • A white precipitate forms (goes cloudy)
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10
Q

What is the chemical reaction taking place when testing for CO2

A
  • Limewater is saturated calcium hydroxide solution
  • Calcium Carbonate is the white precipitate formed with water when reacting
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11
Q

How to test for chlorine

A
  • Place damp blue litmus paper in a sample of the gas
  • It wil be bleached white
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12
Q

What is the chemical reaction occuring, when testing for chlorine

A
  • Chlorine dissolves into the dampness (water) and removes colour from blue litmus
  • It is a good bleaching agent
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13
Q

How to test for ammonia

A
  • Place damp red litmus paper in sample of gas
  • It will turn blue
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14
Q

What is the chemical reaction taking place when testing for ammonia

A
  • Ammonia acts as a base accepiting H+ ions from water
  • OH- ions remain
  • Alkaline so turns litmus blue
  • Ammonia + water -> Ammonium + hydroxide
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15
Q

Describe how to conduct a flame test

A
  • Dip a piece of nichrome / platinum wire into hydrochloric acid to clean the wire
  • Dip the wire into the sample of solid or solution
  • Place the tip of the wire into a non-luminous bunsen flame
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16
Q

Red flame test result

A

Li+

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17
Q

Yellow flame test result

A

Na+

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18
Q

Lilac flame test result

A

K+

19
Q

Orange-red flame test result

A

Ca 2+

20
Q

Blue-green flame test result

A

Cu 2+

21
Q

Flame test result of Li+

A

Red

22
Q

Flame test result for Na+

A

Yellow

23
Q

Flame test result for K+

A

Lilac

24
Q

Flame test result for Ca 2+

A

Orange-red

25
Q

Flame test result for Cu 2+

A

Blue-green

26
Q

How to carry out a NaOH test

A
  • Dissolve sample in water
  • Add a few drops of NaOH (aq)
27
Q

Cu 2+ result - NaOH test

A

Blue precipitate forms

28
Q

Fe 3+ result - NaOH test

A

Brown precipitate forms

29
Q

Fe 2+ result - NaOH test

A

Green precipitate forms

30
Q

How to carry out ammonium test

A
  • Dissolve sample in water
  • Add NaOH (aq) and warm it
  • Test the gas evolved with red litmus paper
  • Red litmus turns blue
31
Q

What is the chemical reaction taking place when carrying out the ammonium test

A

Ammonium ions (from sample), and OH - ions (from NaOH) form ammonia

32
Q

How to test for halides

A
  • Dissolve the sample in water
  • Add nitric acid
  • Add silver nitrate
33
Q

What ion gives a cream precipitate in silver nitrate test

A

Br -

34
Q

What ion gives a white precipitate in the silver nitrate test

A

Cl -

35
Q

What ion gives a yellow precipitate in the silver nitrate test

A

I -

36
Q

Why must you add nitric acid when carrying out a silver nitrate test

A
  • Ag + ions form precipitates with other anions
  • The HNO3 reacts with those anions preventing false positives
37
Q

Why must you add nitric acid when carrying out a silver nitrate test

A
  • Ag + ions form precipitates with other anions
  • The HNO3 reacts with those anions preventing false positives
38
Q

How to test for a carbonate

A
  1. Add hydrochloric acid and look for effervescence
  2. If there is effervescene bubble the gas through limewater
  3. If ions are present, the gas evolved (CO2) turns limewater cloudy
39
Q

Why must you bubble the gas evolved from a carbonate test through limewater

A

Acids evolve gases that aren’t CO2, so it prevents false positives

40
Q

How to test for a sulfate

A
  • Add hydrochloric acid and look for effervescence
  • If there’s no effercescence add barium chloride solution
  • If the ions are present, they will form a white precipitate with the Ba 2+ ions from the BaCl2
41
Q

Why must you still add HCl to a sample testing for a sulfate ion

A
  • Carbonate ions also form a white precipitate with Ba 2+ ions
  • It prevents a false positive
42
Q

Why must you bubble the gas evolved from a carbonate test through limewater

A

Acids evolve gases that aren’t CO2, so it prevents false positives

43
Q

What is the chemical reaction occuring, when testing for chlorine

A
  • Chlorine dissolves into the dampness (water) and removes colour from blue litmus
  • It is a good bleaching agent

GCSE (71 decks)

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