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chemistry > Topic 8 - chemical analysis > Flashcards

Topic 8 - chemical analysis Flashcards

1
Q

what is a pure substance

A

something that only contains one compound or element throughout -not mixed with anything

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2
Q

how can you test the purity of a sample and what will impurities do to your sample

A

by measuring its melting and noiling point and comparing it with the melting or boiling point of the pure substance
the closer your measured value is to the actual value, the purer the substance is .
impurities in your sample will lower the melting point and increase the melting range of your substances.
impurities will lso increase boiling point and may resuly in your sample boiling at a range of different temperatures

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3
Q

what is a formulation

A

a usefull mixture with a precise purpose that is made by following a formula .
Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties

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4
Q

give examples of formulations

A

Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods, cosmetics

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5
Q

what is chromatography

A

an analytical method used to seperate the substances in a mixture
youcan then use it to identify the substance

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6
Q

what are the two phases in chromatography

A

mobile phase- where the molecules can move . this is always a liquid or a gas
stationary phase 0 where the molecules cant move. this can be a solid or a really thick liquid

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7
Q

where will the components in a mixture normally seperate out

A

in the stationary phase so long as all the components spend different amounts of time in the mobile phase.

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8
Q

how many spots will a pure substance form

A

1

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9
Q

what does the speed a chemical moves depend on (chromatography)

A

how its distributed between the two phases
whether it spends more time in the mobile or stationary phase
the chemicals that spend more time in the mobile phase will move further

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10
Q

during paper chromatography , what is the stationary phase and what is the mobile phase

A

stationary phase - chromatography paper
mobile phase - solvent (e.g. ethanol or water )

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11
Q

what does the amout of time the molecules spend in each phase of chromatography depend on

A

how solublle they are in the solvent
how attracted they are to the paper
molecules with a higher solubility in the solvent and which are less attracted to the paper will spend more time in the mobile phase - they will be carried further up the paper

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12
Q

what do we call the result of chromatography analysis

A

chromatogram

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13
Q

what is an Rf value and what is the equation for it

A

the ration between the distance travelled by the dissolved substances and the distance travelled by the solvent .
Rf=distancemovedbysubstance/distancemovedbysolvent

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14
Q

howhow does chromatography help identify substances in a mixture

A

run a pure sample of the substance alongside the unknown mixture .
if the rf values of thereference and one of the spots in the mixture is a match , the substance may be present .

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15
Q

what is the Rf value dependant on

A

the solvent- if you change the solvent the Rf value for a substance iwll change

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16
Q

describe the steps to carry out a paper chromatography

A
  1. get chromatography paper and drawa straight horizontal line with a ruler and pencil across it , 1 cm from the bottom .
  2. place a dot of sample on the pencil line
  3. place the bottom of paper in solvent
  4. make sure the line doesnt touch the solvent
  5. solvent moves up the paper dissolving the substances
17
Q

what is the test for hydrogen

A

hold a lit splint at the open end of a test tube with hydrogen
it will relight with a squeaky pop

18
Q

what is the test for carbon dioxide

A

bubbling carbon dioxide through an aqueous solution of calcium hydroxide , limewater causes the solution to turn cloudy

19
Q

what is the test for oxygen

A

The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.

20
Q

what is the test for chlorine

A

The test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.

21
Q

what are carbonates

A

substances that contain CO 3 ^ 2- ions

22
Q

how do u test for carbonate ions in a mystery solution

A

putting a sample in a test tube and then using a dropping pipette to add a couple of drops of dilute acid .
connect the test tube to a test tube of limewater .
if carbonate ions are present , carbon dioxide will be released that will turn the lime water cloudy when it bubb;es

23
Q

what is the test for sulfate ions

A

using a dropping pipette add a couple drops of dilute hydrochloric acid followed by a couple drops of barium chloride solution. to a test tube containing your mystery solution .
if sulfate ions are present a white precipitate will form

Ba ^2+ (aq) + SO4 ^2- (aq) -> BaSO4(s)

24
Q

what is the test for halides

A

add a couple drops of dilute nitric acid followed by a couple drops of silver nitrate solution to your mystery solution

Ag+ (aq) + Cl- (aq) -> AgCl(s) A chloride gives a white precipitate of silver chloride

Ag+ (aq) + Br- (aq) -> AgBr (s) A bromide gives a cream precipitate of silver bromide

Ag+ (aq) + I- (aq) -> Agl (s) An iodide gives a yellow precipitate of silver iodide

25
Q

what colour do lithium ions burn with

A

crimson flame

26
Q

what colour do sodium ions burn with

A

yellow flame

27
Q

what colour do potassium ions burn with

A

lilac flame

28
Q

what colour do calcium ions burn with

A

orange red flame

29
Q

what colour do copper ions burn with

A

green flame

30
Q

describe how you would carry out flame tests to identify metal ions

A

get a clean platinum wire loop by dipping it in dilute HCL and hold it in a blue flame from a bunsen burner until it burns with no colour.
then dip the loop into the sample you want to test andplace it in theflame.
record the colour of the flame
you can use these colours to detect and identify different ions
it only works for samples that contain a single metal ion/
if it contains a mixture of metal ions. the flame colours of some ions may be hidden by others .

31
Q

how can sodium hydroxide identify metal ions

A

man metal hydroxides are insoluble and precipitate out of solution when formed
some have characteristic colours
add a few drops of sodium hydroxide to a mystery compound solution and wat for an insoluble hydroxide to form

32
Q

what colour is the precipitate of each of these ions when sodium hydroxide is added
calcium
copper (11)
iron (11)
iron (111)
aluminium
magnesium

A

white
blue
green
brown
white at first, redissolves in excess NaOH to form a colourless solution
white

33
Q

what are the ionic equations for precipitate formation of each of these ions
calcium
copper (11)
iron (11)
iron(111)
aluminium
magnesium

A

Ca2+ (aq) + 2OH- (aq) -> Ca(OH)2 (s)

Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)

Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)

Fe3 + (aq) + 3OH- (aq) -> Fe(OH)3 (s)

Al3+ (aq) + 3OH- (aq) -> Al(OH)3 (s)

Mg2+ (aq) + 2OH- (aq) -> Mg(OH)2 (s)

34
Q

what are the advantages of using machines ofver conducting tests

A

sensitive - can detect tiny amounts of substances
fast and tests can be automated
very accutrate

35
Q

how does flame emission spectroscopy work

A

a sample is placed in a flame
as the ions heat u[ their eletrons become excited
when they drop back to original energy levels they tranfer energy as light
the light passes through a spectroscpope which can detect different wavelengths of light to produce a line spectrum
the combination of wavelengths emmited depends on its charge and electron arrangement.

36
Q

what does the intenity of spectrum indicate

A

oncentration of that ion in the solution

37
Q

why is flame emmision spectroscopy more usefull than flame ests

A

can be used to identify ions in a mixture

chemistry (9 decks)

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