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Science - Chemistry - GCSE > P2 - Chemical Analysis > Flashcards

P2 - Chemical Analysis Flashcards

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1
Q

What does ‘pure’ mean in chemistry ?

A

A substance that only contains one compound or element all the way through, and is not mixed with anything else.

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2
Q

How can you test how pure a known substance is ?

A

By measuring its melting or boiling point, you can then compare this value with the melting or boiling point of the pure substance, this value can be found in a data book . And the closer your measured value is to this, the purer your sample is.

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3
Q

What will impurities in the substance do ?

A

They will lower the melting point of the substance, and may also cause the sample to melt across a wider range of temperatures, and will increase the boiling point of the substance, and may also cause the sample to boil across a range of temperatures.

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4
Q

What are formulations ?

A

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

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5
Q

What are some examples of formulations ?

A

Paints, cleaning products, fuels, medicines, cosmetics, fertilisers, metal alloys and food and drink.

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6
Q

What is chromatography ?

A

A method used to separate substances in a mixture, and to identify the substances.

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7
Q

What are the two phases of chromatography ?

A

The mobiles phase - where the molecules can move (in paper chromatography this is a solvent) and the stationary phase - where they can’t move ( in paper chromatography this is the paper).

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8
Q

What happens during paper chromatography ?

A

The solvent moves up the paper, carrying the substances in the mixture with it.

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9
Q

What is the ‘distribution’ in terms of chromatography ?

A

The amount of time a chemical spends dissolved in the solvent or stuck on the paper.

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10
Q

How does the solubility of chemicals affect the results ?

A

The more soluble, the more time it spends dissolved in the solvent - meaning it will move further up the paper.

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11
Q

Why do chemicals separate in chromatography ?

A

The different chemicals will be dissolved for different amounts of time, so different chemicals will move different distances up the paper.

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12
Q

What are chromatograms ?

A

They show the results of chromatography experiments.

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13
Q

what is the solvent front ?

A

The furthest point the solvent reached up the paper.

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14
Q

What is actually shown in the chromatography experiment ?

A

The chemicals move different distances up the paper so the different spots show different chemicals. The number of spots is the smallest possible number of chemicals in the mixture.

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15
Q

What happens if two chemicals move the same distance up the paper ?

A

This means they’ll form one spot between them, you can then repeat the experiment with a different solvent to get a chromatogram with a different number of spots.

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16
Q

What happens if the substance is pure ?

A

You will only get one spot in lots of different solvents, meaning there’s only one chemical in the substance.

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17
Q

What is the R(lower small)f value ?

A

The ratio between the distance travelled by the dissolved substances and the distance travelled by the solvent. The further a substance moves through the stationary phase the larger this value.

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18
Q

How do you calculate the R(lower small)f value ?

A

Distance moved by substance ÷ Distance moved by solvent

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19
Q

How can you use chromatography to see if a mixture contains a certain substance ?

A

Run pure samples of the substance (references) next to the mixture, if the R(lower small)f value of the reference matches one of the spots in the mixture the substance could be in the mixture.

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20
Q

How can you test for chlorine ?

A

Put a piece of litmus paper in the container, chlorine bleaches damp litmus paper, turning it white.

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21
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.

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22
Q

What makes up limewater ?

A

Calcium hydroxide

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23
Q

How can you test for carbon dioxide ?

A

Bubbling it through a limewater solution, if the gas is carbon dioxide it will turn cloudy. You can also just shake gas with the solution.

24
Q

What is the ‘squeaky pop’ test ?

A

Where you hold a lit splint at the open end of a test tube containing hydrogen, you’ll hear a squeaky pop sound.

25
Q

What is an anion ?

A

A negative ion.

26
Q

What are carbonates ?

A

Substances that contain CO3 2- ions.

27
Q

How can you test for carbonate ions ?

A

Using a dropping pipette to add a few drops of dilute acid to the substance, connect this to a test tube containing limewater and if carbonate ions are present their reaction with the acid will release carbon dioxide which when bubbled through limewater will turn it cloudy.

28
Q

What is the reaction between a metal carbonate and an acid ?

A

metal carbonate + acid –> carbon dioxide + salt + water

29
Q

What is the test for sulfates ?

A

Using a dropping pipette add a couple drops of dilute hydrochloric acid and then a couple drops of barium chloride solution, if the mystery solution contains sulfate ions a white precipitate of barium sulfate will form.

30
Q

Why is hydrochloric acid added when testing for sulfate ions ?

A

To get rid of any traces of carbonate ions before doing the actual test as they would also produce a precipitate confusing the results.

31
Q

What is the half-equation for a reaction between a sulfate ion and barium chloride ?

A

Ba 2+ + SO4 2- –> BaSO4

32
Q

What is the test for halide ions ?

A

Add a couple drops of dilute nitric acid (NHO3) and then a couple drops of silver nitrate solution (AgNO3) to the mystery solution.

33
Q

What is the positive result for the test for Cl halide ion ?

A

Should give a white precipitate of silver chloride.

34
Q

What is the positive result for the test for Br halide ion ?

A

Should give a cream precipitate of silver bromide.

35
Q

What is the positive result for the test for I halide ion ?

A

Should give a yellow precipitate of silver iodide.

36
Q

What are the half equations between silver nitrate and the halides ?

A

Ag+(aq) + Cl-(aq) –> AgCl(s)
Ag+(aq) + Br-(aq) –> AgBr(s)
Ag+(aq) + I-(aq) –> AgI(s)

37
Q

What are cations ?

A

Positive ions.

38
Q

How can you test for certain metals ?

A

Using a flame test - some metals produce a characteristic colour when heated in a flame, or a sodium hydroxide test.

39
Q

What colour flame do lithium ions produce ?

A

Li+ ions produce a crimson flame.

40
Q

What colour flame do sodium ions produce ?

A

Na+ ions produce a yellow flame.

41
Q

What colour flame do potassium ions produce ?

A

K+ ions produce a lilac flame.

42
Q

What colour flame do calcium ions produce ?

A

Ca2+ produce an orangy red flame.

43
Q

What colour flame do copper ions produce ?

A

Cu2+ produce a green flame.

44
Q

How can you do the flame test with solid metal ?

A

Clean a nichrome or platinum loop and collect a sample of the mystery metal and put it back in the flame and record its colour.

45
Q

How do you clean nichrome wires ?

A

By rubbing with fine emery paper then holding it in a blue flame from a bunsen burner, it might change colour for a bit but when it goes back to blue it’s clean.

46
Q

How can you do a flame test with a metal in solution ?

A

Soak a splint in the solution and hold over the flame and record the flame colour, or use a spray bottle and spray the solution over the flame.

47
Q

When would a flame test not work ?

A

If the samples you’re using contains a mixture of metal ions, the flame colours of some ions may be hidden by others.

48
Q

How does a sodium hydroxide test work ?

A

Many metal hydroxides are insoluble and precipitate out of solution when formed and they have a characteristic and identifiable colour.

49
Q

How do you perform a sodium hydroxide test ?

A

You add a few drops of sodium hydroxide solution to the mystery compound to form an insoluble coloured hydroxide, which you can then identify.

50
Q

What colour precipitate does calcium form ?

A

White - Ca2+(aq) + 2OH-(aq) –> Ca(OH)2(s)

51
Q

What colour precipitate does copper(II) form ?

A

Blue - Cu2+(aq) + 2OH-(aq) –> Cu(OH)2(s)

52
Q

What colour precipitate does iron(II) form ?

A

Green - Fe2+(aq) + 2OH-(aq) –> Fe(OH)2(s)

53
Q

What colour precipitate does iron(III) form ?

A

Brown - Fe3+(aq) + 3OH-(aq) –> Fe(OH)3(s)

54
Q

What colour precipitate does aluminium form ?

A

White at first but redissolves in excess and goes colourless - Al3+(aq) + 3OH-(aq) –> Al(OH)3(s)

55
Q

What colour precipitate does magnesium form ?

A

White - Mg2+(aq) + 2OH-(aq) –> Mg(OH)2(s)

56
Q

P

A

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Science - Chemistry - GCSE (10 decks)

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