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Chemistry GCSE Paper 2 > Topic 8 - Chemical Analysis > Flashcards

Topic 8 - Chemical Analysis Flashcards

1
Q

What is a pure substance, not in chemistry?

A

A substance with nothing added, in its natural state.

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2
Q

What is a pure substance in chemistry?

A

Something that only contains one compound or element throughout, not mixed with anyone else.

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3
Q

How can you test the purity of a sample?

A

Measure its melting or boiling point and compare it with the melting or boiling point of the pure substance (from data book), this is because chemically pure sustances will melt or boil at a specific temperature. The closer your measured value is to the actual melting or boiling point, the purer the sample.

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4
Q

What will impurities do to a sample?

A

Lower the melting point and increase the melting range. Also, increase the boiling point and could boil at a range of temperatures.

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5
Q

What are formulations?

A

Useful mixtures with a precise purpose that are made by following a formula. Each component in a formulation is present in a measured quantity, and contributes to the properties of the formulation so that it meets its required function.

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6
Q

What are paints composed of?

A

Pigment, solvent, binder (resin) and additives.

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7
Q

What is the use of pigment in paint?

A

Gives colour. Titanium oxide used in white paints.

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8
Q

What is the use of solvent in paint?

A

Used to dissolve other components and alter the visosity.

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9
Q

What is the use of binder in paint?

A

Forms a film that holds the pigment in place after it’s been painted on.

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10
Q

Why are formulations important in the pharmaceutical industry?

A

Chemists can alter the formulation of a pill to make sure it delivers the drug to the correct part of the body at the right concentration. Also that it is consumable and has a long enough shelf life.

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11
Q

What is a use of formulations in everyday life?

A

Found in cleaning products, fuels, cosmetics, fertilisers, metal alloys and food/ drink.

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12
Q

What is chromatography?

A

An analytical method used to seperate the substances in a mixture. You can then use it to identify the substances.

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13
Q

What are the two phases in chromatography?

A

The mobile phase, the stationary phase.

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14
Q

What is the mobile phase?

A

Where molecules can move. Always a liquid or gas.

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15
Q

What is a stationary phase?

A

Where molecules can’t move. This can be a solid or a really thick liquid.

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16
Q

What does how quickly a chemical moves in chromatography depend on?

A

How it is distributed between the stationary and mobile phase. Whether it spends more time in which phase.

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17
Q

If a chemical spends more time in the mobile phase than the stationary phase, what does this mean?

A

It will move further through the stationary phase.

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18
Q

What will a pure substance look like in chromatography?

A

Only ever form one spot in any solvent as there is only one substance in the sample.

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19
Q

What is the stationary phase during paper chromatography?

A

The chromatography paper.

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20
Q

What is the mobile phase during paper chromatography?

A

The solvent, eg. ethanol or water.

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21
Q

What does the amount of time molecules spend in each phase depend on?

A

How soluble they are in the solvent, how attracted they are to the paper.

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22
Q

What will molecules with a high solubility do?

A

Molecules with a high solubility and which are less attracted to the paper will spend more time in the mobile phase and be carried further up the paper.

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23
Q

What is a chromatogram?

A

The result of chromatogrpahy analysis.

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24
Q

What is an Rf value?

A

The ration between the distance travlled by the dissolved substance (solute) and the distance travelled by the solvent. The further through the stationary phase a substance moves, the larger the Rf value.

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25
Q

How can you calculate the Rf value?

A

Rf=distance travelled by substance/ distance travelled by solvent.

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26
Q

Why may chromatography be carried out?

A

To see if a certain substance is present in a mixture.

27
Q

How can you use chromatography to see whether a certain substance is present in a mixture?

A

Run a pure sample of that substance alongside the unknown mixture, If the Rf values of the referance and one of the spots in the mixture match, the substance may be present.

28
Q

What is Rf value dependent on?

A

The solvent.

29
Q

How can you test for chlorine?

A

Chlorine bleaches damp litmus paper, turing it white.

30
Q

Why may chlorine turn litmus paper red at first?

A

It is acidic.

31
Q

How can you test for oxygen?

A

Put a glowing splint inside a test tube containing oxygen, the oxygen will relight the glowing splint.

32
Q

How can you test for carbon dioxide?

A

Bubbling carbon dioxide through an aqueous solution of calcium hydroxide (limewater) causes the solution to turn cloudy.

33
Q

How can you test for hydrogen?

A

Hold a lit splint at the open end of a test tube containing hydrogen you’ll get a squeaky pop sound.

34
Q

What does the ‘squeaky pop’ sound come from?

A

Hydrogen burning quicky with oxygen in the air to form H2O.

35
Q

How can you test for carbonates?

A

Add dilute acid to the sample. Bubble this into limewater. If carbonate ions are present carbon dioxide will be released turning the limewater cloudy.

36
Q

How can you test for sulphate ions?

A

Add a couple drops of dilute hydrochloric acid and barium chloride solution to test tube containing the solution. If sulphate ions are present, a white precipitate of barium sulphate will form.

37
Q

How can you identify halide ions?

A

Add dilute nitric acid and silver nitrate solution to the mystery solution.

38
Q

What is the positive result for carbonates?

A

Cloudy limewater.

39
Q

What is the positive result for sulphates?

A

White barium sulphate precipitate.

40
Q

What is the positive result for chlorine?

A

White precipitate of silver chloride.

41
Q

What is the positive result for bromine?

A

Cream precipitate of silver bromide.

42
Q

What is the positive result for iodine?

A

Yellow precipitate of silver iodide.

43
Q

What colour flame does Lithium ions burn with?

A

Crimson.

44
Q

What colour flame does Sodium ions burn with?

A

Yellow.

45
Q

What colour flame does Potassium ions burn with?

A

Lilac.

46
Q

What colour flame does Calcium ions burn with?

A

Orange-red.

47
Q

What colour flame does Copper ions burn with?

A

Green.

48
Q

Describe how you would carry out a flame test?

A

Clean a platinum wire loop by dipping it in some dilute HCl and then holding it in a blue flame from a Bunsen burner until it burns without any colour. Then dip the loop into the sample you want to test and put it back in the flame. Record the colour of the flame.

49
Q

Why does a flame test only work with samples that only contain a single metal ion?

A

In a mixture of metal ions, the flame colours of some ions may be hidden by the colours of others.

50
Q

How can you test for some different transition metals?

A

Add a few drops of sodium hydroxide to a solution of the compound.

51
Q

What colour precipitate does calcium give?

A

White.

52
Q

What colour precipitate does copper (II) give?

A

Blue.

53
Q

What colour precipitate does iron (II) give?

A

Green.

54
Q

What colour precipitate does iron (III) give?

A

Brown.

55
Q

What colour precipitate does aluminium give?

A

White - redissolves with excess NaOH to form a colourless solution.

56
Q

What colour precipitate does magnesium give?

A

White.

57
Q

Give the ionic equation for a calcium precipitate forming.

A

Ca2+ (aq) + 2OH- (aq) = Ca(OH)2 (s).

58
Q

What happens during flame emission spectroscopy?

A

A sample is placed in a flame. As the ions heat up the electrons become excitied. When the electrons drop back to their original energy levels, they transfer energy as light. The light passes through a spectroscope which can detect different wavelengths of light to produce a line spectrum.

59
Q

What does the combination of wavelengths emitted by an ion depend on?

A

Its charge and its electron arrangement. Since no two ions have the same charge and arrangement, diffent ions emit different wavelengths of light, so each ions produces a different pattern of wavelengths, and has a different line spectrum.

60
Q

What does the intensity of the spectrum indicate? What does this mean?

A

The concentration of the ion in the solution. So line spectrums can be used to identify ions in solution and calculate their concentrations.

61
Q

What is another use for flame emmision spectroscopy?

A

Identify different ions in mixtures. More useful than flame tests which only work for substances containing a single metal ion.

62
Q

What is instrumental analysis?

A

Tests that use machines.

63
Q

What are advantages of instrumental analysis?

A

Very sensitive - can detect the tiniest amounts of substances.
Very fast - can be automated.
Very accurate.

Chemistry GCSE Paper 2 (4 decks)

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