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GCSE Chemistry > Chemical Analysis > Flashcards

Chemical Analysis Flashcards

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1
Q

In chemistry what is a pure substance

A

A substance made up of single element or compound, not
mixed with any other substances

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2
Q

In everyday language, what is a pure
substance

A

A substance that has had nothing added to it, in its
natural state

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3
Q

What are the boiling and melting points
like for pure substances

A

At a fixed (specific) temperature e.g. pure water would
boil at 100°C

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4
Q

What are the boiling and melting points
like for an impure (mixture) substances

A

Over a range e.g. salty water would boil from 100 - 105°C

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5
Q

What is a formulation

A

A mixture that has been designed as a useful product

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6
Q

How are formulations made

A

By mixing components in carefully measured quantities to get the required properties

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7
Q

Examples of formulations

A
  • Fuels
  • Cleaning agents
  • Paints
  • Medicines
  • Alloys
  • Fertilisers
  • Foods
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8
Q

A method used to separate dyes

A

Chromatography

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9
Q

What two phases are involved in
chromatography

A

Stationary and mobile phase

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10
Q

What is the stationary phase?

A

The chromatography paper

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11
Q

What is the mobile phase?

A

The solvent (usually water but can be any liquid e.g. ethanol)

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12
Q

What must you use when drawing the line
on the chromatography paper? Why?

A

Pencil
This is insoluble in the solvent so will not run

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13
Q

Where must the water be in relation to
the pencil line? Why?

A

Water line must be below the pencil line
To stop the inks mixing with the solvent

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14
Q

What does the distance the dots move tell
you?

A

How soluble the ink is in the solvent – if it moves to the
top it is very soluble

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15
Q

If the dot doesn’t move off the pencil line
what does that tell you?

A

The ink is insoluble in the solvent

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16
Q

Explain how the inks are separated using
paper chromatography.

A

Inks have different solubility’s
This means they move up the paper at different speeds/
distances

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17
Q

What is the Rf value

A

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

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18
Q

How can you express Rf Rf =

A

distance dot travelled ÷ distance solvent travelled

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19
Q

What value is Rf always below

A

1

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20
Q

How do we use the Rf values?

A

They are used to identify substances. Each substance has a specific Rf value so we use these to confirm what is in a mixture.

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21
Q

How many spots would you get for a pure
substance

A

One

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22
Q

How many spots would you get in a
mixture

A

More than one

23
Q

What is the test for hydrogen

A

Burning splint
Makes squeaky pop noise

24
Q

What is the test for oxygen

A

Glowing splint
Splint relights

25
Q

What is the test for carbon dioxide

A

Bubble through limewater (calcium hydroxide solution)Limewater turns milky (cloudy)

26
Q

What is the test for chlorine

A

Use damp litmus paper
Turns bleached white

27
Q

What test can be used to identify ions
which produce a colour when burnt

A

Flame test

28
Q

What metal ions produce distinctive
colours in flame tests

A

Lithium
Sodium
Potassium
Calcium
Copper

29
Q

What flame colour does lithium produce

A

Crimson red

30
Q

What flame colour does sodium produce

A

Yellow

31
Q

What flame colour does potassium produce

A

Lilac

32
Q

What flame colour does calcium produce

A

Orange-red

33
Q

What flame colour does copper produce

A

Green

34
Q

Someone wants to identify a metal ion in a
tablet, what must they do first?

A

Crush so in powder
Or dissolve in water

35
Q

What happens if there is a mixture of ions
in a sample

A

Some flame colours can be masked

36
Q

What hydroxide can be used to identify
some metal ions in solution

A

Sodium hydroxide

37
Q

What ions can be tested for using sodium
hydroxide

A

Aluminium,
Magnesium,
Calcium,
Iron (II),
Iron (III),
Copper (II)

38
Q

What colour precipitate is formed for
aluminium, calcium and magnesium with
sodium hydroxide

A

White precipitate

39
Q

How can you distinguish between
aluminium, calcium and magnesium if they
all form a white ppt with sodium
hydroxide

A

Add excess sodium hydroxide
Aluminium hydroxide precipitate will dissolve

40
Q

What colour precipitate is formed with
copper (II) and sodium hydroxide

A

Blue

41
Q

What colour precipitate is formed with
iron (II) and sodium hydroxide

A

Green

42
Q

What colour precipitate is formed with
iron (III) and sodium hydroxide

A

Brown

43
Q

Half equation to show the formation of the
blue ppt between copper (II) and sodium
hydroxide

A

Cu2+ + 2OH- → Cu(OH)2

44
Q

How do you test for a carbonate

A

React with a dilute acid
Forms carbon dioxide gas
Identified using limewater, goes cloudy

45
Q

How do you test for a halide

A

Silver nitrate solution
Presence of dilute nitric acid
Precipitates form

46
Q

What colour precipitate is formed
between a chloride and silver nitrate

A

White precipitate

47
Q

What colour precipitate is formed
between a bromide and silver nitrate

A

Cream

48
Q

What colour precipitate is formed
between a iodide and silver nitrate

A

Yellow

49
Q

How do you test for a sulphate

A

Barium chloride in the presence of dilute hydrochloric acid

50
Q

What colour precipitate is formed
between a sulphate and barium chloride

A

White

51
Q

What are the advantages of instrumental
methods

A

Accurate,
More sensitive (can detect when have small amounts of the substance)
Rapid
Ease of use (operators don’t need chemical skills)
Reliable/ efficient
Sample doesn’t get used up

52
Q

What instrumental method can be used to
detect metal ions in solution

A

Flame emission spectroscopy

53
Q

How is flame emission spectroscopy
carried out

A

Sample is put in a flame

Light given out is passed through a spectroscope

The output is a line spectrum

GCSE Chemistry (7 decks)

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