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Chemistry GCSE > Chemical analysis > Flashcards

Chemical analysis Flashcards

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1
Q

How to conduct a flame test practical

A
  • Dip the loop of an unreactive metal wire such as nichrome or platinum in dilute acid,and then hold it in the blue flame of a Bunsen burner until there is no colour change.
  • This cleans the wire loop and avoids contamination:
    . This is an important step as the test will only work if there is just one type of ion present.
    . Two or more ions means the colours will mix, making identification erroneous.
  • Dip the loop into the solid sample and place it in the edge of the blue Bunsen flame.
  • Avoid letting the wire get so hot that it glows red otherwise this can be confused with a flame colour.
  • The colour of the flame is observed and used to identify the metal ion present:
    . Li+ - Red, Na+-yellow, K+-lilac, Ca2+-Orange-red, Cu2+-blue-green.
  • The sample needs to be heated strongly, so the Bunsen burner flame should be on a blue flame.
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2
Q

How can metal cations in aqeuous solution be identified?

A
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3
Q

paper chromotography-

A

equipment: beaker, pencil line/base line, solvent front, lid
- to identify the individual compounds in the mixture
- capillary tube dipped into dye
- placed on
mobile phase: solvent
stationary phase: chromotography paper

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4
Q

why do we do the baseline in pencil?

A
  • solvent in pen will move up the paper
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5
Q

Lid use

A

To prevent the solvent- water and alcohol from evaporating

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6
Q

solvent line low

A

dye will not move up if the paper is already submerged in solvent

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7
Q

Rf value (retention factor)

A

distance travelled by the sample/dye/ distance travelled by solvent front

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8
Q

Highest retention factor

A

more attracted it is to the solvent

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9
Q

Oxygen test

A

glowing splint, relights

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10
Q

cloudy solution forming

A

precipitate has formed

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11
Q

hydrogen test

A

lit splint, squeaky pop (a result of the rapid combustion of hydrogen with oxygen to produce water)

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12
Q

carbon dioxide test

A

bubble through limewater (aqueous solution of calcium hydroxide), goes cloudy

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13
Q

chlorine

A

damp litmus paper, turns red (as acids are produced when chlorine comes into contact with water) and then bleaches white

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14
Q

Cation tests

A
  • flame tests

- NaOH precipitate

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15
Q

Flame test colours

A 
Na- orange-yellow
K- lilac
Cu- green
Ca- brick red 
Li- crimson
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16
Q

NaOH- metal cations

A
  • Add solution to sodium hydroxide and observe colour
    Most transition metals produce hydroxides with distinctive colours.
  • Cu^2+ +OH- –>Cu (OH)2 (s) - blue
  • Fe^2+ + OH- –> Fe(OH)2 (s)- green
  • Fe^3+ +OH- –> Fe(OH)3 (s)- brown
    WHITE PPT
  • Al^3+ + OH- –> Al(OH)3 (s)
  • Ca^2+ OH- –> Ca(OH)2 (s)
  • Mg^2+ OH- –> Mg(OH)2 (s)
    1, Add excess NaOH –> Al (OH)3 ppt will dissolve
    2, Then do flame test (calcium will produce brick red flame)
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17
Q

CO3 2- (carbonate) tests- anion

A

1, Add dilute acid
CaCO3 + HCL –> CO2 + CaCl2 + H20
2, (CO2 from products )Bubble through limewater –> cloudy precipitate

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18
Q

SO4 2- (sulphate)

A

1, Add an acid dilute HCL –> remove carbonate ions (sulphuric acid will produce a false positive result- could produce a precipitate)
2, Add a few drops of aqueous barium chloride-
3, If a sulfate is present, a white precipitate of barium sulfate is produced.
Ba^ 2+ + SO4 ^ 2- –> BaSO4 (s) (white precipitate)

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19
Q

Halide tests (Cl-, Br-, I-)

A

1, Add acid HNO3- to remove any carbonate ions that might give a false positive result.
The acidification step in the halide ion test must be done with nitric acid rather than hydrochloric acid, as HCl contains chloride ions which would interfere with the results.
2, Add AgNO3 soln + observe ppt colour
Ag+ + Cl- –> AgCl (s) white
Ag+ + Br- –> AgBr (s) cream
Ag + + I- –> AgI (s) yellow

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20
Q

Flame emission spectroscopy

A

1, pass sample through flame
2, pass the light through spectroscope
ADV: sample can be small, accurate and rapid

line spectrum- analyse and identify substance

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21
Q

What is a pure substance?

A

A single element or compound that is not mixed with any other substance.

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22
Q

examples of pure substances

A
  • Diamond (C) is a pure substance because it contains only carbon atoms.
  • Oxygen (O2) is a pure substance because it contains only oxygen molecules
  • Glucose (C6H12O6) is a pure substance because it contains only glucose molecules
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23
Q

Mixture

A

It contains more than one substance

eg: orange juice, soap, milk

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24
Q

Pure water melting and boiling point

A
  • boiling point - 100 degrees Celsius

- melting point - 0 degrees Celsius

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25
Q

What happens to a pure substance at melting point and boiling point?

A
  • They change state but the temperature remains constant at these values.
26
Q

Pure water boiling temperature

A

stays 100 degrees C

27
Q

Pure water freezing temperature

A

0 degrees Celsius

28
Q

Over a range of temperatures, mixtures …

A

change state

29
Q

Examples of mixtures changing state (car)

A
  • car radiator contains a mixture of antifreeze and water so that the mixture freezes below 0 degrees Celsius
  • salt is put on roads to create a mixture with water that freezes below 0 degrees Celsius
  • Petrol is a mixture of hydrocarbons that boil over a range of temperatures from about 60 to 100 degrees Celsius.
30
Q

Salt water

A
  • freezes at a range of temperatures below 0 degrees Celsius between -5 degrees Celsius and -10 degrees Celsius depending how much salt is dissolved.
  • this is used to stop ice forming on roads in winter
  • grit, which contains salt, is put on roads to prevent water freezing if the temperature drops below 0 degrees Celsius.
  • Salt water boils at temperatures above 100 degrees Celsius, eg: between 101 and 103 depending how much salt is dissolved.
31
Q

Antifreeze

A
  • mixed with water in car radiatiors to stop the water freezing in cold weather
  • melting point of antifreeze is -13 degrees C and water is 0 degrees C.
  • mixture typically has a melting point range between -30 degrees C to -40 degrees C depending on how much antifreeze is used.
32
Q

Petrol

A
  • mixture of hydrocarbons
  • boils over a range of temperatures between 60 to 100 degrees Celsius.
  • Each individual substance in petrol has its own specific boiling point, but the mixture boils over a range of temperatures.
33
Q

Formulation

A

A mixture that has been designed as a useful product. (made by mixing together several different substances in carefully measured quantities to ensure the product has the required properties).

34
Q

Alloys

A
  • They are specific mixtures of metals with other elements (eg: steel is a mixture of iron and carbon; brass is a mixture of copper and zinc).
  • Alloys are harder than pure metals
  • there are many different alloys
  • Each alloy is designed to have the specific properties required for its use.
35
Q

Fertilisers

A
  • most fertilisers contain specific mixtures of different substances (eg: many fertilisers contain ammonium nitrate, phosphorous oxide and potassium oxide)
  • There are many different types of fertiliser with different amounts of different substances in them that are suitable for different plants and/or different soil types
36
Q

Fuels

A
  • Many fuels are specific mixtures (eg: petrol and diesel are complex and carefully controlled mixtures of hydrocarbons designed to burn well and power a car engine).
37
Q

Medicines

A
  • Many medicines are specific mixtures of substances (eg: aspirin tablets contain several other substances besides aspirin, including corn starch which is there to bind the tablet together. Calpol contains paracetamol in malitol liquid so the medicine can be taken off a spoon).
38
Q

Cleaning agents

A
  • They are specific mixtures (eg: some dishwasher tablets contain detergents, alkalis, bleaches, rinse aid etc. Some toilet cleaners contain bleaches, alkalis, detergents etc. some oven cleaner sprays contain sodium hydroxide to react with dirt, butane as a propellant)
39
Q

Foods

A
  • Many foods are very specific mixtures (margarine is a mixture of vegetable oils, water, emulsifiers, salt etc. Tomato ketchup is a mixture of tomatoes, vinegar, sweeteners, spices, salt etc. vegetable soup is a mixture of water, vegetables, spices etc.)
40
Q

Paints

A
  • They are mixtures whose contents include a solvent (water for emulsion, hydrocarbons for gloss), pigments (colour) and binder (to hold the pigments in place when the paint dries).
41
Q

Chromotography

A
  • It is a very useful technique that can be used to separate and analyse mixtures. There are several types of chromotography including paper, thin layer, column and gas chromatography.
42
Q

Pure substance

A

-may consist of a single element or compound which contains no other substances

43
Q

Mixture

A
  • consists of two or more elements or compounds that are physically mixed together, they are not chemically combined
  • chemical properties of the substances in a mixture remain unchanged
  • Substances in mixtures can be separated by physical means
44
Q

Distinguishing purity

A
  • Pure substances melt and boil at specific and sharp temperatures e.g. pure water has a boiling point of 100°C and a melting point of 0°C
  • Mixtures have a range of melting and boiling points as they consist of different substances that tend to lower the melting point and broaden the melting point range
  • Melting and boiling points data can therefore be used to distinguish pure substances from mixtures
  • Melting point analysis is routinely used to assess the purity of drugs
  • This is done using a melting point apparatus which allows you to slowly heat up a small amount of the sample, making it easier to observe the exact melting point
  • This is then compared to data tables
  • The closer the measured value is to the actual melting or boiling point then the purer the sample is
45
Q

Cooling curves

A
  • The influence of impurities can be more clearly seen on a heating / cooling curve
  • If the temperature of a liquid is measured as it cools and freezes the data can be used to produce a graph
  • The following graph shows the cooling curve for a sample of a compound
  • The horizontal part of the graph shows that the compound has a sharp melting point, so the compound is pure
  • An impure sample of the compound would produce a gradual decrease in temperature as it freezes
46
Q

definition of a formulation

A

-A formulation is a mixture that has been designed for a specific purpose to deliver a commercial product

47
Q

Formulations

A

-Every part of the formulation is present in carefully measured quantities so that each component provides the required properties
-eg: paint-
contains the following substances in exact quantities:
.pigment-gives the paint colour
.Binder-forms a film that holds the pigment in place
.solvent-used to dissolve the other components and alter the viscosity.
-Formulations are not compounds as the components are not chemically combined.

48
Q

Where are formulations very important?

A

In the pharmaceutical industry, where the exact ratios of each component must be precise.
-By changing the formulation of a particular medicine chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that it’s safe to consume and has an adequately long shelf life

49
Q

The information on the packaging of some products tells you the formulation as a

A

percentage composition

50
Q

Chromatography

A
  • used to separate substances and provide information to help identify them
  • the components have different solubilities in a given solvent and different adhesion to the supporting medium-usually paper
  • a pencil line is drawn on chromatography paper and spots of the sample are placed on it
  • pencil is used for this as ink would run into the chromatogram (the name given to the visual output of the chromatography run) along with the samples
  • the paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent so the samples don’t wash into the solvent container
  • the solvent travels up the paper by capillary action,taking some of the coloured substances with it
  • different substances have different solubilities so will travel at different rates, causing the substances to spread apart
  • the substances with higher solubility will travel further than the others
  • this is because they spend more time in the mobile phase and are thus carried further up the paper than the less soluble components.
51
Q

What can the pigments in ink be analysed by?

A

Paper chromatography

52
Q

All chromatography techniques use two phases called the

A

mobile phase and the stationary phase

53
Q

What is the mobile phase in paper chromatography?

A
  • the solvent in which the sample molecules can move, which in paper chromatography is liquid eg: water or ethanol
54
Q

What is the stationary phase in paper chromatography?

A

-the actual chromatography paper itself

55
Q

Distinguishing pure and impure substances

A
  • Pure substances will produce only one spot on the chromatogram
  • If two or more substances are the same, they will produce identical chromatograms
  • If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
  • An impure substance therefore will produce a chromatogram with more than one spot
56
Q

Identifying substances using Rf values

A

-These values are used to identify the components of mixtures
-The Rf value of a particular compound is always the same but it is dependent, however, on the solvent used
-If the solvent is changed then the value changes
-Calculating the Rf value allows chemists to identify unknown substances because it can be compared with -Rf values of known substances under the same conditions
-These values are known as reference values
-Retention factor = distance moved by compound ÷ distance moved by solvent
-The Rf value is a ratio and therefore has no units
NOTE: Both distances are measured from the baseline

57
Q

Where should chlorine be handled and why?

A

-It should be handled in a fume cupboard due to its toxicity

58
Q

Advantages of instrumental methods

A
  • Advancements in technology and computing have allowed for the development of instruments designed to analyse chemical substances
  • Methods of analysis include X-ray, Infra-Red and Mass Spectroscopy, Gas Chromatography and Flame Photometry
  • These analytical techniques require modern day instruments which are a vital part of chemistry laboratories
  • The advantage of using these instruments over more traditional methods include:
  • They provide greater accuracy
  • They are faster and easier to use
  • They are automated and can perform multiple simultaneous sampling and testing
  • Modern instruments are very sensitive and can work with very small sample sizes
59
Q

Uses of instrumental methods of analysis

A
  • to analyse blood,urine and tissue samples in hospitals
  • to analyse the contents of foods
  • to monitor the quality of water and air
  • to monitor the purity of medicines
60
Q

Flame emission spectroscopy

A
  • when some metal ions are heated in a flame, they give off a distinctive colour
    -Sometimes it can be difficult to judge which ion is giving the colour.
  • it is an example of an instrumental method of analysis
    -it is used to:
    .identify metal ions in solution
    .measure the concentration of metal ions in solution
    .identifies metal ions with more certainty than flame tests and can measure the concentration of metal ions in a solution which flame tests cannot
    -the actual wavelength of the light given off is measured by a spectroscope in the machine.
    -each metal ion gives off light at its own specific wavelength producing a line spectrum
    -this allow the identity of ions to be found with certainty
    -the concentration of the ions in the solution can also be found by measuring the intensity of a wavelength of light given out. The more intense the light it gives out, the higher the concentration of that ion.
    (the intensity of the light from the sample can be measured and the conc found by graph-although this is usually done directly by a computer controlling the instrument).

Chemistry GCSE (14 decks)

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