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AQA GCSE Chemistry > Chemical Tests etc. > Flashcards

Chemical Tests etc. Flashcards

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1
Q

What is a pure substance?

A

A substance which is a single element or compound

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2
Q

What is a mixture?

A

A substance that contains two or more substances not chemically joined and easily separated using a physical property

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3
Q

What is important about the boiling and melting points of pure elements and compounds?

A

Pure compounds and elements melt and boil at fixed, specific temperatures

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4
Q

What is the test for pure water?

A

If the water boils at 100 degrees centigrade

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5
Q

What is important about the boiling and melting points of impure elements and compounds?

A

They have a range of melting and boiling points

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6
Q

What is the melting point?

A

The temperature at which heat gives energy to the particles so they move further apart and the forces of attraction weaken

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7
Q

What is the boiling point?

A

The temperature at which heat gives more energy so the particles have lots of energy and the forces of attraction between them completely break to let the particles move freely

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8
Q

What is condensation?

A

When the particles have less energy so they move slower so forces of attraction become greater and particles stick together in an irregular way. They become a liquid

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9
Q

What is freezing?

A

When particles have a lot less energy so the forces of attraction become strong and the particles stick together in a regular way to make a solid

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10
Q

What do impurities do to the melting point?

A

lower the melting point and increase the melting point range

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11
Q

What do impurities do to the boiling point?

A

increase the boiling point and give a boiling point range

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12
Q

What is a formulation?

A

A mixture that has been designed as a useful product. Typically complex mixtures in which each chemical has a particular purpose

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13
Q

How are formulations made?

A

By mixing the components in carefully measured quantities to ensure that the product has the required properties

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14
Q

Descibe how you carry out the chromatography experiment?

A

1) Use a ruler to draw a horizontal pencil line 2cm from the bottom of the chromatography paper
2) mark five pencil spots at equal intervals across the origin line
3) using a different capillary tube for each coloring, put a small spot of each colouring on four of the pencil spots
4) Use another capillary tube to put a small spot of the unknown mixture on the last pencil spot
5) pour water into the beaker to a depth no more than 1cm
6) clip the top of the paper to a wooden spill and rest on top of beaker. The bottom of the paper should dip in the solvent
7) wait for the water solvent to travel at least 3/4 of the way up the paper
8) remove the paper from the beaker and draw another pencil line as close to the wet edge as possible, this is the solvent front line
9) hang the paper up to dry thoroughly

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15
Q

How do you calculate an Rf value?

A

distance moved by solute / distance moved by solvent

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16
Q

Why must a lid be put on top of the beaker in chromatography?

A

to prevent the evaporation of the solvent

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17
Q

Why should the origin line be drawn in pencil?

A

as ink (pen) would dissolve in the solvent

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18
Q

Why should the pencil line and spots be above the level of the solvent?

A

so that the spots do not dissolve into the solvent in the beaker

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19
Q

What is chromatography used for?

A

to separate mixtures which can give information to help identify substances

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20
Q

How many spots will a pure substance generate?

A

one

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21
Q

How many spots will a mixture generate?

A

more than one spot (one for each substance in the mixture)

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22
Q

What is the stationary phase?

A

The chromatography paper

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23
Q

What is the mobile phase?

A

The solvent

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24
Q

How does chromatography work?

A

1) mixture dissolves in the mobile phase as it moves through the stationary phase
2) the mixture is also interacting with the stationary phase (constantly switiching between phases)
3) the more soluble a component of the mixture, the further it will travel
4) different components have different Rf values

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25
Q

Why do different substances travel different distances up the chromatography paper?

A
  • susbtances that have a stronger attraction to the solvent (more soluble), move quickly and travel a long way up the paper
  • substances that have a stronger attraction to the paper, move slower and travel a short distance up the paper
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26
Q

What is an Rf value?

A

the ratio of the distance moved by a compound to the distance moved by the solvent

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27
Q

Why would a permanent marker have an Rf value of 0?

A

Because they are insoluble so don’t dissolve in the solvent and travel up the paper

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28
Q

What does a large Rf value indicate?

A
  • the substance is very soluble

- the substance spent a longer time in the mobile phase

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29
Q

Why would substances be heated in an oil bath, not directly in a Bunsen burner flame to calculate melting and boiling points?

A

A Bunsen burner would heat the substance too quickly, making it difficut to judge the temperatures at which substances start and finish melting

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30
Q

How can a more reliable result be given for chromatography experiments?

A
  • repeating the experiment using a different solvent
  • calculate the different Rf values and compare with the previous
  • the Rf values should match relative to the other substances
31
Q

How does chromatography separate substances?

A
  • different substances will be distributed differently between the mobile phase and the stationary phase
  • the substances will separate because they spend different amounts of time in the mobile phase depenedent on their solubility
  • and therefore they move different distances up the paper
32
Q

How can paper chromatography be used to identify what impurity is present in the substance/mixture

A
  • run the mixture alongside pure samples of the possible impurity
  • if the spot from one of the possible impurities moves the same distance as the mixture, then it indicates that that is the impurity
  • this is the same if the calculated Rf values match
33
Q

What is the colour of the flame for lithium testing?

A

crimson

34
Q

What is the colour of the flame for sodium testing?

A

yellow

35
Q

What is the colour of the flame for potassium testing?

A

lilac

36
Q

What is the colour of the flame for calcium testing?

A

orange-red

37
Q

What is the colour of the flame for copper testing?

A

green

38
Q

What are the limitations to the flame tests?

A
  • it is diffucult to judge the colour
  • individuals see colour differently
  • results quoted (expected flame colours) are only for pure substances
  • if a mixture of ions is in the flame test, they can mask the colour of one ion
39
Q

What is the test and result for carbon dioxide?

A

bubble gas into limewater and if carbon dioxide, the limewater will turn cloudy

40
Q

What is the test and result for hydrogen?

A

adding a lit splint to the gas, and if hydrogen, the gas will burn rapidly with a squeaky pop sound

41
Q

What is the test and result for chlorine?

A

add damp litmus paper to the gas and if chlorine, it bleaches the paper white

42
Q

What is the test and result for oxygen?

A

put a glowing splint into the gas and if oxygen, the splint will relight

43
Q

What are cations?

A

Positively charged metal ions

44
Q

What must react to form a solid precipitate?

A

Two liquids

45
Q

What is added to the solution of metal ions to form the coloured precipitates?

A

Sodium Hydroxide

46
Q

What is formed when NaOH is added to Calcium?

A

White precipitate

47
Q

What is formed when NaOH is added to magnesium?

A

White precipitate

48
Q

What is formed when NaOH is added to aluminum (3+)?

A

White precipitate

49
Q

What is formed when NaOH is added to iron (2+)?

A

Green precipitate

50
Q

What is formed when NaOH is added to iron (3+)?

A

Brown precipitate

51
Q

What is formed when NaOH is added to copper (2+)?

A

Blue precipitate

52
Q

Which metal ion’s precipitate dissolves when in excess NaOH?

A

Aluminium (III)

53
Q

What is the general ionic formula for testing cations?

A

Metal Ion + Hydroxide = Metal(Hydroxide)

54
Q

What is an anion?

A

Negatively charged ion

55
Q

What is the test for a sulfate anion?

A
  • add barium chloride and hydorchloric acid to a metal sulfate
56
Q

What is the test result for a sulfate anion?

A

White precipitate formed

57
Q

What is the test for a carbonate anion?

A

Add an acid to a metal carbonate. Bubble the gas produced into limewater

58
Q

What is the test result for a carbonate anion?

A

Limewater turns from clear to cloudy showing carbon dioxide gas has been made

59
Q

What is the test for halide anions?

A

Add halide solution to a test tube
Add Nitric acid
Add silver nitrate solution

60
Q

What is the test result for a chloride ion?

A

white precipitate formed

61
Q

What is the test result for a bromide ion?

A

cream precipitate formed

62
Q

What is the test result for an iodide ion?

A

yellow precipitate formed

63
Q

What can occur when a sample containing a mixture of ions is used in a flame test?

A

The colour of the flame can be masked

64
Q

Why is HCl added in the sulfate test and HNO3 added in the halide tests?

A

To remove impurities

65
Q

What are the uses of instrumental analysis?

A
  • analyse blood, tissue and urine samples
  • analyse the content of food
  • monitor the quality of water and air
  • monitor the purity of water
66
Q

What are the advantages of instrumental analysis compared to chemical tests?

A
  • rapid, information ca be gained very quickly
  • sensitive, only a small amount of a substance needs to be used
  • informative - provides a lot of valuable information about a substance
  • very accurate
67
Q

What are the disadvantages of instrumental analysis compared to chemical tests?

A
  • equipment required is expensive
  • requires an operator with special training
  • results have to be compared with results from known samples which have to have been obtained
68
Q

What is flame emission spectroscopy?

A

An instrumental analysis method used to identify metal ions in a solution as well as their concentration

69
Q

What is the flame emission spectroscopy method?

A
  • place the sample into a flame
  • as the ions in the sample heat up, their electrons become exited and rise to a higher energy level
  • when the electrons drop back down to their original energy level, they transfer energy as light which passes through a spectroscope
  • the spectroscope detects different wavelengths of light to produce a line spectrum specific to that ion
70
Q

How can the ions be identified from a line spectrum?

A

Each ion gives a unique pattern of lines so the spectra of the mixtures of ions can be identified by comparing it to known spectra of metal ions

71
Q

What does the intensity of the spectrum indicate?

A

The concentration of an ion in a sample (more intense = more concentrated)

72
Q

What indicates a solution is acidic?

A

If blue litmus paper turns red in it

73
Q

What happens to the pH of water when carbon dioixide is in it?

A

It goes acidic

74
Q

What type of wire is used in flame tests?

A

A nichrome wire

AQA GCSE Chemistry (10 decks)

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