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Chemistry > C12 Chemical Analysis > Flashcards

C12 Chemical Analysis Flashcards

1
Q

What is a pure substance

A

A sample containing only one element or compound

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2
Q

How is purity worked out

A

Pure substances have specific melting and boiling points

The closer the value of an experiment are to those in the data book, the greater the purity of a sample

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3
Q

What happens in the two phases of chromatography

A

Substances are picked up and carried by a mobile phase (liquid or gas)

The mobile phase then moves through a stationary phase (solid or viscous liquid)

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4
Q

How are substances separated in chromatography

A

They are distributed across the two phases

A substance moves far if it’s more attracted to the mobile phase

A substance doesn’t move far if it’s more attracted to the stationary phase

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5
Q

What happens in paper chromatography

A

Mixtures of soluble substances are separated

A solvent (mobile phase) is run through the mixture on paper (contains the stationary phase)

The substances will move up the paper at different rates

The most soluble substance will move the furthest

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6
Q

How is retention factor calculated

A

Distance travelled by substance / distance travelled by solvent

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7
Q

What is a reference substance

A

A pure substance run next to the tested substance to see if it’s a component in the mixture

This is evidence, not proof

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8
Q

What affects how far components travel in paper chromatography

A

The less attracted to the paper, the further it travels

The more soluble in the solvent, to further it travels

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9
Q

What does the process of chromatography produce that can be analysed?

A

Chromatogram

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10
Q

What can the number of spots produced by a mixture depend on

A

Solvent used

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11
Q

How is hydrogen tested for

A

Place a lit splint next to the mouth of the test tube

A squeaky pop shows the presence of hydrogen

This is produced due the rapid burning of hydrogen in the presence of oxygen to give H20

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12
Q

How is oxygen tested for

A

Insert a glowing splint into the test tube

The splint relighting shows the presence of oxygen

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13
Q

How is carbon dioxide tested for

A

Bubble the gas into an aqueous solution of lime water (calcium hydroxide)

The lime water going cloudy shows the presence of carbon dioxide

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14
Q

How is chlorine tested for

A

Insert damp litmus paper into the test tube

The paper bleaching shows the presence of chlorine

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15
Q

What is a flame test

A

Some positive metal ions produce characteristic flame colours that can be used to identify the ion

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16
Q

What does Li+ produce in a flame test

A

Crimson flame

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17
Q

What does Ca2+ produce in a flame test

A

Orange-red flame

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18
Q

What does Na+ produce in a flame test

A

Yellow flame

19
Q

What does Cu2+ produce in a flame test

A

Green flame

20
Q

What does K+ produce in a flame test

A

Lilac flame

21
Q

Why is it problematic for interpreting the results of a flame test if a sample is made up of multiple ions?

A

If the sample consists of a mixture of metal ions, the flame colours of some may be masked, which can lead to incorrect interpretations

22
Q

What metal hydroxides create white precipitates from aqueous solutions when reacted with sodium hydroxide

A

Calcium hydroxide
Ca2+

Magnesium hydroxide
Mg2+

Aluminium hydroxide
Al3+
Can dissolve in excess producing a colourless solution

23
Q

What are precipitates

A

Insoluble solids

24
Q

What metal hydroxides create coloured precipitates in aqueous solutions from a reaction with sodium hydroxide

A

Copper(II) hydroxide
Cu2+
Blue

Iron(II) hydroxide
Fe2+
Green

Iron(III) hydroxide
Fe3+
Brown

25
Q

How are carbonates tested for

A

A reaction between a carbonate and a dilute acid produces carbon dioxide

We can use the standard carbon dioxide test to work out if an unknown substance is a carbonate

26
Q

What ions are carbonates characteristic of

A

CO3 2-

27
Q

What products are formed from carbonates and dilute acids

A

Salt

Carbon dioxide

Water

28
Q

How are halides tested for

A

A reaction between halides and silver nitrate from a precipitate

The colour of the precipitate can determine what ions are present

29
Q

What colour precipitate do chlorine ions produce when reacted with liver nitrate

A

White

30
Q

What colour precipitate do bromine ions produce when reacted with sliver nitrate

A

Cream

31
Q

What colour precipitate do iodine ions produce when reacted with sliver nitrate

A

Yellow

32
Q

Why is dilute nitric acid added to a solution before testing for halides

A

This removes carbonate ions

These could disrupt results by forming a precipitate with silver ions

33
Q

How are sulfates tested for

A

A reaction between sulfates and barium chloride forms a white precipitate

34
Q

Why is dilute hydrochloric acid added to a solution before testing for sulfates

A

This removes carbonate ions

These could disrupt results by forming a precipitate with barium ions

35
Q

What ions are sulfates characteristic of

A

SO4 2-

36
Q

What ions do halogens typically form

A

Halide anions

E.g. K-, Br-

37
Q

What are the disadvantages of instrumental methods

A

Instruments are often expensive

Need special training to operate

Results are only useful when compared to data from known substances

38
Q

What are the advantages of instrumental methods

A

Greater sensitivity and accuracy

Quicker at producing results

Able to analyse tiny samples

39
Q

What is flame emission spectroscopy

A

Instrumental method used to identify and find the concentration of metal ions present in a solution

40
Q

How are flame emission spectroscopies carried out

A

Sample of metal solution is placed into a flame

The light that is given off is captured by a spectroscope

This instrument generates a line spectrum by distinguishing between light with different wavelengths

41
Q

How are line spectra from flame emission spectroscopies analysed to identify ions

A

Each metal ion will generate a new line spectrum

This means that we can identify all ions present in a solution

42
Q

How are line spectra from flame emission spectroscopies analysed to find the concentration ions

A

The concentration of an ion is indicated by the intensity of line spectra

43
Q

What are reference spectra

A

A known spectrum from a specific metal ion used to analyse data through comparison

Chemistry (4 decks)

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