Topic 8 - chemical analysis

Question 1

what is a pure substance

Answer 1

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

Question 2

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

Answer 2

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

Question 3

what is a formulation

Answer 3

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

Question 4

give examples of formulations

Answer 4

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

Question 5

what is chromatography

Answer 5

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

Question 6

what are the two phases in chromatography

Answer 6

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

Question 7

where will the components in a mixture normally seperate out

Answer 7

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

Question 8

how many spots will a pure substance form

Answer 8

1

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

what do we call the result of chromatography analysis

Answer 12

chromatogram

Question 13

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

Answer 13

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

Question 14

howhow does chromatography help identify substances in a mixture

Answer 14

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 .

Question 15

what is the Rf value dependant on

Answer 15

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

Question 16

describe the steps to carry out a paper chromatography

Answer 16

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

Question 17

what is the test for hydrogen

Answer 17

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

Question 18

what is the test for carbon dioxide

Answer 18

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

Question 19

what is the test for oxygen

Answer 19

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

Question 20

what is the test for chlorine

Answer 20

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

Question 21

what are carbonates

Answer 21

substances that contain CO 3 ^ 2- ions

Question 22

how do u test for carbonate ions in a mystery solution

Answer 22

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

Question 23

what is the test for sulfate ions

Answer 23

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)

Question 24

what is the test for halides

Answer 24

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

Question 25

what colour do lithium ions burn with

Answer 25

crimson flame

Question 26

what colour do sodium ions burn with

Answer 26

yellow flame

Question 27

what colour do potassium ions burn with

Answer 27

lilac flame

Question 28

what colour do calcium ions burn with

Answer 28

orange red flame

Question 29

what colour do copper ions burn with

Answer 29

green flame

Question 30

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

Answer 30

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 .

Question 31

how can sodium hydroxide identify metal ions

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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)

Question 34

what are the advantages of using machines ofver conducting tests

Answer 34

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

Question 35

how does flame emission spectroscopy work

Answer 35

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.

Question 36

what does the intenity of spectrum indicate

Answer 36

oncentration of that ion in the solution

Question 37

why is flame emmision spectroscopy more usefull than flame ests

Answer 37

can be used to identify ions in a mixture