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Chemistry > C12 - Chemical Analysis > Flashcards

C12 - Chemical Analysis Flashcards

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1
Q

What is a pure substance

A

A pure substance is one that is made up of only one substance. It can either be an element or a compound

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2
Q

Examples of pure substances

A
  • Distilled water
  • Helium
  • Pure ethanol
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3
Q

What is special about a pure substances melting and boiling points?

A

They are fixed and exact

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4
Q

What do impurities do to a substance?

A

They generally lower the melting point and raise the boiling

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5
Q

How can you identify an impure substance?

A

They don’t have a set melting/ boiling point; they melt/boil over a range

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6
Q

What is a formulation

A

A formulation is a mixture that has been designed to give a useful product

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7
Q

Examples of formulations

A
  • Medicinal drugs
  • Paint
  • Washing up liquid
  • Cosmetics
  • Fertilisers
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8
Q

What are the two different phases in chromatography

A
  • The mobile phase (solvent)
  • The stationary phase (usually paper )
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9
Q

What does a high affinity to the mobile phase do

A

The substance moves further up

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10
Q

What does a high affinity to the stationary phase do

A

The substance doesn’t move up as far

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11
Q

How to calculate the Rf (retention factor)

A

Distance moved by substance / distance moved by solvent

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12
Q

Test for hydrogen

A

Lightened splint will make a squeaky pop with hydrogen

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13
Q

Test for oxygen

A
  • Use hydrogen peroxide to make oxygen
  • Glowing splint will be relit
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14
Q

Test for carbon dioxide

A

Limewater (calcium hydroxide) goes cloudy due to carbonate precipitate forming

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15
Q

Test for chlorine

A

Damp blue litmus paper will turn white (get bleached)

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16
Q

How to carry out a flame test

A
  • Dip nichrome wire in acid and flame to clean and in acid again
  • Dip in metal
  • The flame may change colour
17
Q

Why is it hard to identity some colours in a flame test

A

Colours like potassium are weak colours and can be masked by stronger colours such as sodium

18
Q

What ions form white precipitates with sodium hydroxide

A
  • Aluminium ions
  • Magnesium ions
  • Calcium ions
19
Q

What happens to an aluminium precipitate in excess NaOH

A

It dissolves unlike a calcium precipitate or a magnesium precipitate

20
Q

What colour precipitate do copper (II) ions form in NaOH

A

Light blue

21
Q

What colour precipitate do iron (II) ions form in NaOH

A

Green

22
Q

What colour precipitate do iron (III) ions form in NaOH

A

Brown

23
Q

Test for carbonates

A
  • Add dilute HCl to sample
  • It will fizz (due to CO₂) if it is a carbonate
  • Gas can then be bubbled through limewater
24
Q

Test for halides

A
  • Pour the sodium halide into test tube
  • Add nitric acid to remove impurities
  • Add silver nitrate
25
Q

Colour of precipitate that chlorine ions give in the halide test

A

White

26
Q

Colour of precipitate that bromine ions give in the halide test

A

Cream

27
Q

Colour of precipitate that iodine ions give in the halide test

A

Yellow

28
Q

Test for sulphates

A
  • Pour sulphate into test tube
  • Add HCl to remove impurities
  • Add barium chloride (if sulphates present, it will go white deu to white precipitate forming)
29
Q

What colour flame do magnesium ions cause

A

No colour

30
Q

Advantages of modern instrumental analysis methods

A
  • Highly accurate and sensitive
  • Quicker
  • Only a small amount of sample needed
31
Q

Disadvantages of modern instrumental analysis methods

A
  • Usually very expensive
  • Require special training to use
  • Specialist training needed to interpret results
  • Results can sometimes only be compared to a data book value
32
Q

What happens during flame emission spectroscopy

A
  • Energy provided by flame excites electrons
  • They jump into higher energy levels
  • When they go back down, they release light energy
33
Q

Test for water vapour

A
  • Use blue cobalt chloride paper
  • IF water vapour is present, it will turn pink (hydrated)
34
Q

Why is the start line drawn in pencil in chromatography

A
  • If we drew it using ink, the ink would move up with the solvent
  • This would affect the results and make them unreadable
35
Q

How to use paper chromatography to identify an unknown substance

A
  • Set up chromatography in standard way with the unknown chemical on the pencil start line
  • Draw a line where the solvent got to (solvent front)
  • Measure the distance moved by the unknown chemical
  • Measure the distance moved by the solvent
  • Use these values in the Rf value equation
  • Look this Rf value up in a database but it may not be on there if the substance has never been analysed
  • This may need to be repeated with different solvents
36
Q

Why does the Rf value not have any units

A

Because it is a ratio of the distance moved by the substance compared to the distance moved by the solvent

Chemistry (17 decks)

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