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Chem Paper 2 > C12: Chemical analysis > Flashcards

C12: Chemical analysis Flashcards

1
Q

What is a pure substance?

A

A single element or compound containing only one type of particle

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2
Q

How can melting and boiling points be used to determine the purity of a substance?

A

A pure substance has a fixed m.p./b.p.
An impure substance melts and boils over a range of temperatures, and are overall higher

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3
Q

What is a formulation?

A

A complex mixture that’s been designed as a useful product. The quantities of each component are carefully measured so that the product has the properties that we need.
e.g. fuels, cleaning products, paint, medicine, alloys, fertilisers and food.

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4
Q

What is paper chromatography?

A

A physical separation technique that allow substances to be separated based on their solubilities.

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5
Q

What is the stationary phase of chromatography?

A

The paper because it doesn’t move

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5
Q

What is the mobile phase of chromatography?

A

The solvent because it moves

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6
Q

What happens to more soluble substances during chromatography?

A

Travel further up the paper

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7
Q

Why is the starting line drawn in pencil?

A

Pen ink is soluble so it’ll move up with the solvent

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8
Q

What is the formula for calculating the rf value?

A

Rf (no units) = distance moved by substance / distance moved by solvent.
Look up rf value in a database to identify the substance

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9
Q

What do you do if 2 substances have the same Rf value?

A

Use a different solvent

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10
Q

Describe the test for hydrogen

A

Insert a burning splint - a pop sound is produced when near hydrogen

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11
Q

Describe the test for oxygen

A

Insert a glowing/smouldering splint - it relights when near oxygen

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12
Q

Describe the test for carbon dioxide

A

Use limewater (aqueous calcium hydroxide). Bubble co2 gas through limewater, if present, limewater turns cloudy

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13
Q

Describe the test for chlorine

A

Insert damp litmus paper into test tube - presence of chlorine bleaches the paper

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14
Q

What is the flame colour of lithium ions?

A

Crimson

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15
Q

What is the flame colour of sodium ions?

A

Yellow

16
Q

What is the flame colour of potassium ions?

A

Lilac

17
Q

What is the flame colour of calcium ions?

A

Orange-red

18
Q

What are the flame colours for copper and beryllium?

A

Green

19
Q

What are problems with using flame tests?

A

Colour can be difficult to distinguish (esp. if there is a low concentration of the compound)
Sample may contain impurities/ a mixture of ions and mask the colour of the flame

20
Q

What else can scientists use, apart from flame tests?

A

Flame emission spectroscopy

21
Q

What is flame emission spectroscopy?

A

A sample of a metal ion in a solution is placed into a flame, the light given out is passed through a spectroscope, which converts the light into a line spectrum. The positions are specific to the metal ion. It can also tell the concentration of a metal ion - lines become more intense with higher conc.

22
Q

What is an instrumental method?

A

A method carried out by a machine

23
Q

Why are instrumental methods good?

A

They are rapid - more so than flame tests
Very sensitive - work on a tiny sample of a metal compound
Accurate

24
Q

What 3 ions do you need to know that react with NaOH?

A

Magnesium, Calcium, Aluminium, Iron, Copper

25
Q

What happens when you add NaOH to the 3 aforementioned ions?

A

White precipitate forms

26
Q

What happens when you add NaOH to iron?

A

Brown precipitate forms (3+)
Green precipitate forms (2+)

27
Q

What happens when you add NaOH to copper?

A

Blue precipitate forms

28
Q

How do you distinguish between Mg, Al and Ca precipitates?

A

Flame tests for calcium

29
Q

Describe the test for the carbonate ion

A

Add dilute acid to sample.
It will react to form a gas and we see fizzing.
Bubble gas through lime water to test for CO2

30
Q

Describe the test for the halide ions

A

Add dilute nitric acid to the sample.
Add dilute silver nitrate solution
Halide ions produce a precipitate of the silver halide. Each one makes a different colour precipitate.
Chloride - white Bromide - cream Iodide - yellow

Chem Paper 2 (8 decks)

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