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Chemistry - Chemical analysis Flashcards

1
Q

Definition of pure in chemistry

A

Only contains one compound or element throughout - not mixed with anything else

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2
Q

What tells you how pure a substance is

A

A chemically pure substance will melt or boil at a specific temperature

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3
Q

How can you test the purity of a sample

A

Measure its melting and boling point and compare it with the melting or boiling point of the pure substance. The closer your measured value is to the actual melting or boiling point, the purer the sample is

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4
Q

What are formulations

A

Mixtures with exact amounts of components, useful with precise purpose eg. paint

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5
Q

What is chromatography

A

An analytical method used to separate the substances in a mixture. You can then use it to identify the substances

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6
Q

What are the phases of chromatography

A

A mobile phase - where the molecules can move. This is always a liquid or a gas
A stationary phase - where the molecules can’t move. This can be a solid or a really thick liquid.

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6
Q

During the chromatography experiment what phase are the substances in

A

The substances in the sample constantly move between the mobile and the stationary phase - an equilibrium is formed between the two phases

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7
Q

How do the two phases of chromatography interact with each other

A

The mobile phase moves through the stationary phase, and anything dissolved in the mobile phase moves with it

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8
Q

What determines how quickly a chemical moves in chromatography

A

The chemicals that spend more time in the mobile phase than the stationary phase will move further. A chemical will spend more time in the mobile phase if it is more soluble in the mobile phase

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9
Q

What is the stationary phase in paper chromatography

A

The paper

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10
Q

What is the formula to calculate the Rf value

A

distance travelled by the substance divided by the distance travelled by the solvent

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11
Q

What is the Rf value specific to

A

The Rf value of a substance is specific to a particular mobile phase and stationary phase, if these phases changed then so would the Rf value

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12
Q

Test for chlorine gas

A

Chlorine bleaches damp litmus paper- will turn it white

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13
Q

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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14
Q

Test for carbon dioxide

A

Bubbling carbon dioxide through (or shaking carbon dioxide with) an aqueous solution of lime water causes it to turn cloudy

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15
Q

Test for hydrogen gas

A

Hold a lit splint at the open end of a test tube containing hydrogen, you’ll get a “squeaky pop”.

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16
Q

How do we test for carbonates in anions

A

Put a sample in a test tube and them using a dropping pipette add a couple of drips of dilute acid. You should then connect the test tube to a test tube of limiter. If carbonate ions are present, co2 will be released and will turn the limewater cloudy when it bubbles through it

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17
Q

What safety precautions are required for testing chlorine gas

A

Do the experiment in a fume cupboard
Wear a mask

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18
Q

How do we test for sulphates in anions

A

Use a dropping pipette to add a couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution a test tube containing the mystery solution. If sulphate ions are present a white precipitate will form.

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19
Q

How to identify a hallide ion

A

Add a couple of drops of dilute nitric acid, followed by a couple of drops of silver nitrate solution.

20
Q

Silver chloride colour

A

A chloride gives a white precipitate of silver chloride

21
Q

Silver bromide colour

A

A bromide gives a cream precipitate for silver bromide

22
Q

Silver iodide colour

A

An iodide gives a yellow precipitate of silver iodide

23
Q

What do flame tests identify

A

Metal ions

24
Q

Lithium ions burn with

A

a crimson flame

25
Q

Sodium ions burn with

A

a yellow flame

26
Q

Potassium ions burn with

A

a lilac flames

27
Q

Calcium ions burn with

A

an orange-red flame

28
Q

Copper ions burn with a

A

green flame

29
Q

How to test for cations

A

Clean a platinum wire loop by dipping it in some dilute HCl and then holding it in a blue flame from a bunsen burner until it burns without any colour. Then, dip the loop into the sample you wang to test and put it back in the flame. Record the colour of the flame.

30
Q

What is the limitation of the flame test

A

Only works for samples that contain a single metal ion. If the sample tested contains a mixture of metal ions, the flame colour of some ions may e hidden by colours of others.

31
Q

How to test for metal hydroxides

A

Add a few drops of sodium hydroxide solution to a solution of your mystery compound. If you get a coloured insoluble hydroxide you can often tell which metal was in the compound.

32
Q

What ppt does calcium ions form

A

White

33
Q

What ppt does copper ions form

A

Blue

34
Q

What ppt does iron form

A

Green

35
Q

What ppt does aluminium form

A

White at first. But then redissolves in excess NaOH to form a colourless solution.

36
Q

What ppt does magnesium form

A

White

37
Q

A chemical reaction is taking place in a test tube. What methods could be used to collect the gas?

A

Place an upside down measuring cylinder over the test tube to trap the gas
Attach the top of the test tube to a gas syringe

38
Q

Why do we add hydrochloric acid when testing for sulphate ions

A

To remove any carbonate ions

39
Q

When testing for halide ions why do we add nitric acid

A

To remove any carbonate or sulphate ions

40
Q

When testing for halide ions, is nitric acid or hydrochloric acid used?

A

Nitric acid

41
Q

What happens during flame emission spectroscopy

A

A sample is placed in a flame. As the ions heat up their electrons become excited. When the electrons drop back to their original energy levels, they transfer energy as light. The light passes through a spectroscope, which c an detect different wavelengths of light to produce a line spectrum.

42
Q

What does the combination of wavelengths emitted by an ion depend on

A
  • the ions charge
  • and the ions electron arrangement
43
Q

What does the intensity of the spectrum indicate and what does this mean

A

The concentration of that ion in solution - means that line spectrums can be used to identify ions in solution and calculate their concentrations.

44
Q

How is fame emission spectroscopy more useful than a flame test

A

Flame tests only work for substances that contain a single metal ion.

45
Q

Advantages of using machines

A
  • they are very sensitive so can detect even the tiniest amount of substances
  • very fast and tests can be automated
  • very accurate
46
Q

When metal ions are heated they start to _____ light

A

emit

47
Q
A

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