Chemical Analysis

Question 1

describe the test for hydrogen

Answer 1

• Remove the bung from the test tube and insert a burning splint
• If hydrogen is present, the hydrogen gas burns rapidly and will produce a pop sound

Question 2

describe the test for oxygen

Answer 2

• use glowing splint and place into test tube of “ oxygen “, if oxygen is present the splint relights and bursts into flames

Question 3

describe the test for carbon dioxide

Answer 3

• limewater used ( limewater is an aqueous solution of calcium hydroxide)
• two test tubes are present ( one w the gas and one w limewater
• draw some of gas into plastic pipette
• Bubble/shake the gas through limewater
• if repeated several times the limewater will turn cloudy( milky)

Question 4

describe the test for chlorine

Answer 4

• Insert damp litmus paper into the mouth of the test tube
  Chlorine bleaches the litmus paper and turns it white

Question 5

in the flame test what colour does lithium produce

Answer 5

crimson flame

Question 6

in the flame test what colour does sodium produce

Answer 6

yellow flame

Question 7

in the flame test what colour does potassium produce

Answer 7

lilac flame

Question 8

in the flame test what colour does calcium produce

Answer 8

orange-red flame

Question 9

in the flame test what colour does copper produce

Answer 9

green flame

Question 10

what solution can be used to identify metal ions

Answer 10

sodium hydroxide solution

Question 11

what colour is formed when sodium hydroxide solution is added to aluminium, calcium and magnesium

Answer 11

white precipitate

Question 12

what is an issue of calcium , aluminium and magnesium when sodium hydroxide solution is added to them

Answer 12

they all produce a white precipitate = hard to distinguish

Question 13

how can we distinguish between aluminium , magnesium and calcium

Answer 13

• if added excess sodium hydroxide is added to aluminium = aluminium precipitate redissolves

Flame test needs to be done to distinguish calcium

Question 14

what is the balanced equation of adding calcium nitrate with sodium hydroxide

Answer 14

calcium nitrate + sodium hydroxide —> sodium nitrate + calcium hydroxide

Question 15

what is the balanced equation of adding magnesium nitrate with sodium hydroxide

Answer 15

magnesium nitrate + sodium hydroxide –> sodium nitrate + mangesium hydroxide

Question 16

what is the balanced equation of adding aluminium nitrate with sodium hydroxide

Answer 16

aluminium nitrate + sodium hydroxide —> sodium nitrate + aluminium hydroxide

Question 17

what does the reaction of copper 11 ( 2) ions and sodium hydroxide produce

Answer 17

a blue precipitate of copper 11( 2) hydroxide

Question 18

what does the reaction of iron 11 ( 2) ions and sodium hydroxide produce

Answer 18

green precipitate of iron 11 ( 2) hydroxide

Question 19

What does the reaction of iron 3 ions and sodium hydroxide produce

Answer 19

brown precipitate of iron (111) hydroxide

Question 20

what is the balanced symbol equation for the reaction of copper 2 ions and sodium hydroxide

Answer 20

Cu ( NO3)2 + 2NaOH -> 2NaO3 + Cu(OH) 2

Question 21

What is the balanced symbol equation for the reaction of iron 2 ions and sodium hydroxide

Answer 21

Fe(NO3)2 + 2NaOH -> 2NaNO3 + Fe(OH)2

Question 22

what is the balanced symbol equation for the reaction of iron 3 ions and sodium hydroxide

Answer 22

Fe(NO3)3 + 3NaOH -> 3NaNO3 + Fe(OH)3

Question 23

describe the test to determine the carbonate ion

Answer 23

• Add dilute acid to sample
• if carbonate is present - the acid will react with the carbonate to make carbon dioxide gas AND Effervescence will be see
• bubble the gas through the lime water . if the lime-water goes cloudy = carbon dioxide proved = that we have started the experiment with a carbonate ion

Question 24

describe the test for halide ions

Answer 24

• add dilute nitric acid to the sample
• add dilute silver nitrate solution
  -halide ions produce a precipitate of the silver halide - each halide makes a different coloured precipitate

Question 25

what colour precipitate is formed from chloride ions

Answer 25

white precipitate of silver chloride

Question 26

what colour precipitate is formed from bromide ions

Answer 26

cream precipitate of silver bromide

Question 27

what colour precipitate is formed from iodide ions

Answer 27

- yellow precipitate of silver iodide

Question 28

describe the test to determine the sulfate ion

Answer 28

- Add dilute hydrochloric acid to our sample - Add barium chloride solution - If sulfate ions are present, there will be a white precipitate present

Question 29

what is flame emission spectroscopy

Answer 29

an instrumental method used to analyse metal ions in solutions.

Question 30

what is the process to carrying out flame tests

Answer 30

1) dip a nichrome wire loop into hydrochloric acid, and heat it in a flame, to clean off any excess chemicals that are on it 2) dip it into the acid again, then dip the loop into the metal compound that is being tested 3) hold the loop in a roaring blue bunsen burner flame 4) use the colour of the bunsen flame to identify the metal ion in the compound

Question 31

what are the problems with flame test

Answer 31

- the colour of the flame test can be difficult to distinguish - this is especially true, if there is only a low concentration of the metal compound - sometimes, a sample contains a mixture of ions, which can mask the colour of the flame - so instead of doing flame tests, scientists use flame emission spectroscopy

Question 32

how does the flame emission spectroscopy method work

Answer 32

- a sample of the metal ion in a solution is placed into a flame - the light given out is passed into a machine, called a spectroscope - the spectroscope converts the light into a line spectrum - the positions of the lines in the spectrum are specific for a given metal ion - this can be used to identify the metal ion - it can also identify the concentration of the metal ion, as the light becomes more intense with higher concentrations

Question 33

what are the advantages of instrumental methods

Answer 33

- they are quicker than flame tests - they are senstive, meaning flame emission spectroscopy can work even on a tiny sample of a metal compound - therefore, they allow very small samples to be analysed - they are highly accurate, and is more likely to identify a metal ion correctly and quickly - if a samples contains multiple metal ions the spectrum will show the lines for all of them

Question 34

what are disadvantages of instrumental methods

Answer 34

- the equipment is usually very expensive - it takes special training to use - it gives results that can often only be interpretated by comparison with data from known substances