Chemical Analysis: Identification of Ions

Question 1

potassium ions

Answer 1

K+

Question 2

what colour flame do potassium ions produce?

Answer 2

lilac

Question 3

copper ions

Answer 3

Cu2+

Question 4

what colour flame do copper 2+ ions produce?

Answer 4

green

Question 5

sodium ions

Answer 5

Na+

Question 6

what colour flame do sodium ions produce?

Answer 6

yellow

Question 7

calcium ions

Answer 7

Ca2+

Question 8

what colour flame do calcium ions produce?

Answer 8

orange-red flame

Question 9

lithium ions

Answer 9

Li+

Question 10

what colour flame do lithium ions produce?

Answer 10

crimson

Question 11

why are flame tests used?

Answer 11

to identify metal ions in ionic compounds

Question 12

flame test practical steps

Answer 12

1. submerge nichrome wire loop in dilute HCl to clean it
2. place nichrome wire into sample being tested
3. hold nichrome wire loop in bunsen burner’s blue flame
4. observe change in colour of bunsen burner flame

Question 13

what colour precipitate do magnesium ions (Mg2+) form?

Answer 13

white precipitate magnesium hydroxide

Question 14

magnesium hydroxide equation

Answer 14

Mg2+ (aq) + 2OH- (aq) –> Mg(OH)2 (s)

Question 15

what colour precipitate do aluminium ions (Al3+) form?

Answer 15

white precipitate aluminium hydroxide

Question 16

aluminium hydroxide equation

Answer 16

Al3+ (aq) + 3OH- (aq) –> Al(OH)3 (s)

Question 17

what does aluminium hydroxide dissolve in?

Answer 17

excess NaOH (forms colourless solutions)

Question 18

what colour precipitate do calcium ions (Ca2+) form?

Answer 18

white precipitate calcium hydroxide

Question 19

calcium hydroxide equation

Answer 19

Ca2+ (aq) + 2OH- (aq) –> Ca(OH)2 (s)

Question 20

what colour precipitate do iron ions (Fe2+) form?

Answer 20

green precipitate iron (II) hydroxide

Question 21

iron (II) hydroxide equation

Answer 21

Fe2+ (aq) + 2OH- (aq) –> Fe(OH)2 (s)

Question 22

what colour precipitate do iron ions (Fe3+) from?

Answer 22

brown precipitate iron (II) hydroxide

Question 23

iron (III) hydroxide equation

Answer 23

Fe3+ (aq) + 3OH- (aq) –> Fe(OH)3 (s)

Question 24

what colour precipitate do copper ions (Cu2+) form?

Answer 24

blue precipitate copper (II) hydroxide

Question 25

copper (II) hydroxide equation

Answer 25

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

Question 26

Test for carbonates?

Answer 26

- add dilute acid to sample - CO2 will be produced, observed by effervescence - bubble gas through limewater to test it

Question 27

what do all carbonates produce?

Answer 27

CO3 2-

Question 28

how to test for halides?

Answer 28

- add dilute nitric acid to unknown solution (removes carbonate ions to ensure they don't form a precipitate) - add dilute silver nitrate - if halide ions are present, they will form a white precipitate with silver ions

Question 29

what colour precipitate is silver chloride?

Answer 29

white

Question 30

silver chloride equation

Answer 30

Ag+ (aq) + Cl- (aq) --> AgCl (s)

Question 31

what colour precipitate is silver bromide?

Answer 31

cream

Question 32

silver bromide equation

Answer 32

Ag+ (aq) + Br- (aq) --> AgBr (s)

Question 33

what colour precipitate is silver iodide?

Answer 33

pale yellow

Question 34

silver iodide equation

Answer 34

Ag+ (aq) + I- (aq) --> AgI (s)

Question 35

how to test for sulfates?

Answer 35

- add dilute HCl to unknown sample (removes carbonate ions which could disrupt results by forming a precipitate) - add barium chloride solution - white precipitate forms if sulfates are present

Question 36

what colour precipitate does barium sulphate form?

Answer 36

white

Question 37

barium sulphate equation

Answer 37

Ba2+ (aq) + SO4 2- (aq) --> BaSO4 (s)

Question 38

advantages of using instrumental methods of chemical analysis

Answer 38

greater sensitivity and accuracy - quicker at producing results - able to analyse tiny samples

Question 39

disadvantages of using instrumental methods of chemical analysis

Answer 39

- expensive - must go through special training to operate the instruments - only useful when compared to data from known substances

Question 40

how does flame emission spectroscopy work?

Answer 40

1. place sample of metal solution being tested into a flame, light will be given off 2. light given off is captured in a spectroscope - instrument generates a line spectrum by distinguishing between light with different wave lengths

Question 41

what does a flame emission spectroscopy analyse?

Answer 41

- identity of metal ions (metal ions generate new lines on spectrum so can identify all ions present in solution) - concentration of metal ions (intensity of line) - reference spectra (analyse mixtures by comparing them with reference spectra)