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GCSE Chemistry > C8 - Chemical Analysis > Flashcards

C8 - Chemical Analysis Flashcards

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1
Q

Define a pure substance

A

only contains one compound or element, not mixed with any other substance

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2
Q

How do you measure a substance’s purity?

A

measure its melting/boiling point and compare it with the melting/boiling point of the pure substance (found in a data book)

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3
Q

Impurities in a solid will …….. the melting point.

A

lower

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4
Q

Impurities in a liquid will ………. the boiling point.

A

raise

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5
Q

Impurities will ……….. the range of temperatures a substance melts or boils at.

A

increase

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6
Q

Define a formulation

A

Formulations are useful mixtures with a specific purpose that are made by following a formula.

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7
Q

Give some uses for chromatography

A
  • detect bombs in airports
  • compare fibres found at a crime scene
  • fingerprinting
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8
Q

What is the mobile phase (chromatography) ?

A

the liquid/gas that moves (the solvent)

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9
Q

What is the stationary phase (chromatography) ?

A

the medium that doesn’t move (chromatography paper)

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10
Q

Describe the chromatography practical

A
  • draw a pencil line near the bottom of a strip of chromatography paper
  • add dots of different inks onto the line
  • place the paper in a beaker with solvent, ensuring the solvent doesn’t touch the line
  • wait for the solvent to absorb up the paper
  • the colour will move up the paper and separate into different colours
  • remove from beaker and add another pencil line where the solvent reached
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11
Q

How do you calculate Rf value?

A

distance travelled by substance / distance travelled by solvent

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12
Q

Why are Rf values useful when interpreting chromatograms?

A

it allows you to identify unknown substances

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13
Q

What is a solvent front?

A

the distance travelled by the solvent - starting from the baseline

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14
Q

Describe how you test for chlorine gas

A

chlorine bleaches damp litmus paper, turning it white

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15
Q

Describe how you test for oxygen

A

use a glowing splint - it will relight if present

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16
Q

Describe how you test for carbon dioxide

A

turns limewater cloudy

17
Q

Describe how you test for hydrogen

A

use a lit splint - you’ll hear a squeaky pop

18
Q

How do you test for carbonates?

A
  • put a sample in a test tube and add a few drops of hydrochloric acid
  • connect to a test tube of limewater
  • warm with a bunsen burner
  • if present, the limewater will turn cloudy
19
Q

How do you test for sulphates?

A
  • add hydrochloric acid, barium chloride and mystery solution into a test tube
  • shake
  • will form a white precipitate if present
20
Q

How do you test for halides?

A
  • add silver nitrate and nitric acid to mystery solution and shake
  • forms a precipitate
  • chloride = white
  • bromide = cream
  • iodide = yellow
21
Q

Describe how you test for metal ions using a flame test

A
  • dip nichrome wire loop into solution
  • place in a roaring blue flame
  • record colour of flame
22
Q

What colour flame is observed for each metal?
lithium
potassium
sodium
calcium
copper

A
  • lithium = crimson
  • potassium = lilac
  • sodium = yellow
  • calcium = orange red
  • copper = green
23
Q

Why is the flame test not very accurate for identifying metal ions?

A
  • mixture of ions are difficult to detect
  • colour is subjective
  • colours can be masked
24
Q

Why is the nichrome wire loop dipped in acid between each test?

A

to avoid cross contamination

25
Q

Which reagent is added to metal ions to perform a precipitate test?

A

sodium hydroxide solution

26
Q

Give the result for each metal ion in a precipitate test
- calcium
- copper (II)
- iron (II)
- iron (III)
- aluminium
- magnesium

A
  • calcium = white
  • copper = blue
  • iron (2) = green
  • iron (3) = brown
  • aluminium = white (dissolves in excess -> goes colourless)
  • magnesium = white
27
Q

Why is a precipitate test often not enough to confirm which metal ion is present in a solution?

A

lots of the results give the same colour (white) precipitate

28
Q

Describe how flame emission spectroscopy works

A
  • a sample is placed in a flame
  • ions heat up and electrons become excited
  • they drop back to their original energy levels and transfer energy as light
  • this light passes through a spectroscope, which produces a line spectrum
29
Q

What are advantages of flame emission spectroscopy?

A
  • you can be certain of the element - unlike flame tests
  • can be used on mixtures
  • intensity of the spectrum tells you the concentration
30
Q

What are advantages of using instrumental analysis (machines) to analyse unknown substances?

A
  • very sensitive - can detect very small amounts of substances
  • very fast
  • very accurate

GCSE Chemistry (10 decks)

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