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Chemistry > Topic 8 - Chemical Analysis > Flashcards

Topic 8 - Chemical Analysis Flashcards

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1
Q

What is a pure substance

A

Something that only contains one compound or element throughout

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2
Q

How can you test the purity of a sample

A

-By measuring its melting or boiling point and comparing it with melting or boiling point with the pure substance from a data book
-The closer the measured value to the actual melting or boiling, the purer the sample is

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3
Q

What does impurities in a sample do to the melting point

A

Lower the melting point therefore increasing the melting range of the substance

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4
Q

What does impurities in a sample do to the boiling point

A

-Increase the boiling point and may result in the sample boiling at a range of temperatures

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5
Q

What are formulations

A

Useful mixtures with a precise purpose that are made by following a formula and each component is present in a measured quantity and contributes to the properties of the formulation so it meets its required function

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6
Q

List compositions of a paint formulation

A

-Pigment = gives the paint colour (e.g. titanium oxide used as a pigment in white paint)
-Solvent = used to dissolve the other components and alter the viscosity
-Binder = forms a film that holds the pigment in place after it’s been painted on
-Additives = added to further change the physical and chemical properties of the paint

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7
Q

Give an example of formulations being useful in the pharmaceutical industry

A

By altering the formulation of a pill, chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that it’s consumable and has a long enough shelf life

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8
Q

Where can formulations be found in everyday life

A

-Cleaning products
-Fuels
-Cosmetics
-Fertilisers
-Metal alloys
-Food and drink

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9
Q

What information do products have about its composition on the packaging

A

It tells you the ratio/percentage of each component telling you that product’s a formulation

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10
Q

Why do products have information about its formulation on its packaging

A

It lets you choose a formulation with the right composition for your particular use

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11
Q

What is the definition of chromatography

A

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

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12
Q

What is a mobile phase in chromatography

A

When the molecules can move - this is always a liquid or a gas

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13
Q

What is a stationary phase in chromatography

A

Where the molecules can’t move. This can be a solid or a really thick liquid

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14
Q

What is the equilibrium in chromatography

A

Between the stationary and mobile as the sample constantly move between these phases

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15
Q

What does how quickly a chemical moves in chromatography depend on

A

How it’s distributed between the two phases - whether it spends more time in the mobile or stationary phase

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16
Q

What to happens to chemicals that spend more time in the mobile phase

A

It will move further through the stationary phaee

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17
Q

How does the mobile phase move

A

Moves through the stationary phase and anything dissolved in the mobile phase will move with it

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18
Q

Why do substances move at different rates in chromatography

A

The different dissolved substances in a mixture are attracted to the two phases in different proportions. This causes them to move at different rates through the paper.

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19
Q

What is the stationary phase in paper chromatography

A

Paper

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20
Q

What is the mobile phase in paper chromatography

A

solvent (e.g. ethanol or water)

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21
Q

What two factors does the amount of time molecules spend in each phase during paper chromatography depend on

A

-How soluble they are in the solvent
-How attracted they are to paper

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22
Q

What factors mean molecules will spend more time in the mobile phase of chromatography

A

-Higher solubility in the solvent
-Less attraction to the paper

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23
Q

What is an Rf value

A

The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent

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24
Q

What makes a larger Rf value

A

The further through the stationary phase a substance moves the higher the Rf value

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25
Q

What is the Rf value equation

A

Rf = distance travelled by the substance / distance travelled by the solvent

26
Q

How would chromatography be used to see if a certain substance is present in a mixture

A

Run a pure sample of the substance alongside the unknown mixture if the Rf values of the reference and one of the spots in the mixture match the substance may be present

27
Q

How does changing the solvent in chromatography help prove if a substance is present in a mixture

A

The Rf value is dependent on the solvent and if it is changed the Rf value will change. Test both pure sample and mixture against a number of different solvents and if the Rf value of the pure substance matches with one of the spots in all the solvents it’s likely the compound is present on the mixture. If only Rf value in some solvents the substance isn’t present.

28
Q

How to detect carbonates ions in a substance

A

Putting a sample of a mystery solution in a test tube and using a dropping pipette to add a couple of drops of dilute acid then connect the tube to another filled with limewater. If the ions are present carbon dioxide will be released turning the limewater cloudy when it bubbles through it.

29
Q

What are carbonates

A

Substances that contain CO3 ions with a charge of 2-

30
Q

How do you test for sulfates with HCl and Barium Chloride

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 (BaCl2) to a test tube containing the mystery solution. If sulfate ions are present, a white precipitate of barium sulfate will form.

31
Q

What is a sulfate ion

A

SO4 charge of 2-

32
Q

How to test for halides with nitric acid and silver nitrate

A

Add a couple of drops of dilute nitric acid (HNO3) followed by a couple of drops of silver nitrate solution, AgNO3 to the mystery solution

33
Q

What should testing for halides with nitric acid and silver nitrate show if positive

A

-A chloride gives a white precipitate of silver chloride
-A bromide gives a cream precipitate of silver bromide
-A iodide gives a yellow precipitate of silver iodide

34
Q

What are the 3 halides

A

Cl- , Br- , I-

35
Q

What colour do Lithium ions burn (Li+)

A

A crimson flame

36
Q

What colour do sodium ions burn (Na+)

A

Yellow

37
Q

What colour do potassium ions burn (K+)

A

Lilac flame

38
Q

What colour do calcium ions burn (2+)

A

Burn with an orange-red flame

39
Q

What colour do copper ions burn (2+)

A

Green flame

40
Q

How do you use flame tests to identify metal ions

A

-Clean platinum wire loop by dipping in dilute HCl and holding it in a blue flame from a bunsen burner until it burns without any colour
-Dip the loop into the sample you want to test and put it back in the flame, the record the colour of the flame

41
Q

Why do flame tests only with samples with a single metal ion

A

If the sample tested contains a mixture of metal ions, the flame colours of some ions may be hidden by the colours of others.

42
Q

Why can you test for metal hydroxides

A

They are insoluble and precipitate out of solution when formed and some hydroxides have a characteristics colour

43
Q

How do you test for metal hydroxides

A

Add a few drops of sodium hydroxide solution to a solution of your mystery compound - all in the hope of forming an insoluble hydroxide

44
Q

What is the colour of precipitate when adding sodium hydroxide to calcium ions (Ca) 2+

A

White

45
Q

What is the colour of precipitate when adding sodium hydroxide to copper (II) ions (2+)

A

Blue

46
Q

What is the colour of precipitate when adding sodium hydroxide to Iron (II) (2+)

A

Green

47
Q

What is the colour of precipitate when adding sodium hydroxide to iron (III) (3+)

A

Brown

48
Q

What is the colour of precipitate when adding sodium hydroxide to aluminium (3+)

A

White at first then re dissolves in excess NaOH to form a colourless solution

49
Q

What is the colour of precipitate when adding sodium hydroxide to Magnesium (2+)

A

White

50
Q

Why can you use a flame test to identify the metal ion in a compound

A

Compounds of some metals burn with a characteristic colour

51
Q

How does flame emission spectroscopy

A

-A sample is placed in flame and as the ions heat up their electrons go up energy levels, and when they drop down to their original energy levels, they transfer energy as light.
-The light passes through a spectroscope which can detect different wavelengths of light to produce a line spectrum

52
Q

What do the combination of wavelength emitted by an ion depend on (2)

A

-Charge of ion
-Electron arrangement

53
Q

Why does each ion produce a different pattern of wavelengths

A

-No two ions have the same charge and electron arrangements so they emit different wavelengths of light

54
Q

What does the intensity of a wavelength spectrum indicate and what does this allow line spectrums to do

A

The concentration of the ion in that solution - so concentrations can be calculated

55
Q

Why does flame emission spectroscopy working for mixtures mean it’s better than flame tests

A

Flame tests can only work for substance that contain a single ion

56
Q

What are the advantages of using machines to analyse substances

A

-Very sensitive so can detect even the tiniest amounts of substances
-Very fast and tests can be automated
-Very accurate

57
Q

What is the test for chlorine

A

-It bleaches damp litmus paper, turning it white (red for a moment at first as a solution of chlorine is acidid)

58
Q

What is the test for oxygen

A

If you put a glowing splint in a test tube containing oxygen it will relight the glowing splint

59
Q

What is the test for carbon dioxide

A

Bubbling CO2 through an aqueous solution of limewater (calcium hydroxide) causes the solution to turn cloudy

60
Q

What is the test for hydrogen

A

-If you hold a lit splint at the open end of a test tube contains hydrogen you’ll get a squeaky pop

Chemistry (9 decks)

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