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Chemistry Paper 2 > Chemical analysis > Flashcards

Chemical analysis Flashcards

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1
Q

What is purity in chemistry?

A

Something that only contains one element or compound

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2
Q

How can the boiling/melting point of a substance tell you how pure it is?

A

All pure substances melt or boil at a specific temperature so the closer the value measured is to the boiling/melting point it is purer.

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3
Q

What will impurities do to your substance?

A

It will lower the melting point and increase the boiling point whilst also increasing the range of temperatures.

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4
Q

What is a formulation?

A

A formulation is a mixture made in a specific way for a specific purpose and recipe.

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5
Q

What can formulations be used for?

A

In the pharmaceutical industry for pills, paint, fuels, cleaning products.

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6
Q

What is paper chromatography

A

It is an analytical method to separate the substances in a mixture.

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7
Q

What is the mobile phase?

A

Where the molecules can move - this is a liquid or a gas.

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8
Q

What is the stationary phase?

A

Where the molecules cannot move- this is a solid or a thick liquid.

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9
Q

What do substances do between the phases and how does this affect how long a molecule moves?

A

Substances move between the two phases and an equilibrium is formed. How far a molecule moves depends on how long it spends in the mobile phase.

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10
Q

Why do some molecules spend in longer in a certain phase?

A

How soluble they are in the solvent and how attracted they are to the paper. If they have a high solubility and are less attracted to the paper they will be in the mobile phase for longer.

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11
Q

How can we analyze what is in a mixture in paper chromatography?

A

The different spots of chemicals will separate and we will see them distributed out.

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12
Q

What is the Rf value?

A

It is the ratio between the dissolved substance and the distance travelled by the solvent front.

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13
Q

How do you calculate the Rf value?

A

distance travelled by substance/ distance travelled by solvent.

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14
Q

How do you test for chlorine?

A

Chlorine bleaches litmus paper but it may turn red for a second.

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15
Q

How do you test for oxygen?

A

Place a glowing splint into a test tube and it will relight if oxygen is present.

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16
Q

How do you test for hydrogen?

A

Place lit splint and there will be a squeaky pop if hydrogen is present.

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17
Q

How do you test for carbon dioxide?

A

Bubble carbon dioxide through limewater and if it is present it will turn cloudy.

18
Q

How do you test for carbonates?

A

Add a couple of drops of dilute acid and then connect it to a tube of limewater. If carbonates are present it will turn cloudy.

19
Q

How do you test for sulfates?

A

Add a few drops of dilute hydrochloric acid and barium chloride to the test tube. If there are sulfate ions present a white precipitate will form.

20
Q

How do you carry out flame tests?

A

Clean a platinum loop with HCL and hold it to a blue bunsen burner until it burns without color. Next, dip the loop into the sample and record the colour of the flame

21
Q

What color flame will lithium ions produce?

A

Crimson

22
Q

What color flame will sodium ions produce?

A

Yellow

23
Q

What color flame will potassium ions produce?

A

Lilac

24
Q

What color flame will calcium ions produce?

A

Orange-red

25
Q

What color flame will copper ions produce?

A

Green

26
Q

How do you test for metals?

A

Metal hydroxides are insoluble and precipitate out of solution. These have certain colors. So add drops of sodium hydroxide solution to the metal.

27
Q

What is the color of the precipitate for calcium?

A

White

28
Q

What is the color of the precipitate for copper?

A

Blue

29
Q

What is the color of the precipitate for iron (II)?

A

Green

30
Q

What is the color of the precipitate for iron (III)

A

Brown

31
Q

What is the color of the precipitate for aluminium?

A

White at first but redissolves in excess NaOH to form a colorless solution.

32
Q

What is the color of the precipitate for magnesium?

A

White

33
Q

How do you test for halides?

A

Add some dilute drops of dilute nitric acid and some silver nitrate solution.

34
Q

What does chloride give as a precipitate?

A

A white precipitate and silver chloride.

35
Q

What does bromide give as a precipitate?

A

A cream precipitate and silver bromide

36
Q

What does iodide give as a precipitate?

A

A yellow precipitate and silver iodide.

37
Q

What is flame emission spectroscopy?

A

A sample is placed in a flame. As the ions heat up the electrons get excited and drop back to their original energy levels and at this point, they transfer energy through light. The light goes through a spectroscope which detects different wavelengths of light to produce a line spectrum,

38
Q

Why is there a different combination of wavelengths?

A

This depends on the charge and electron arrangement so they will emit different wavelengths of light.

39
Q

What does the intensity of the light indicate?

A

The concentration of the ion.

40
Q

Why is flame emission spectroscopy better than flame tests?

A

They can be used for mixtures, not just a single ion.

41
Q

What are the advantages of flame emission spectroscopy?

A

Accurate, fast, and sensitive.

Chemistry Paper 2 (5 decks)

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