qualitative analysis

Question 1

what are the 7 cations?

Answer 1

1. aluminium (AL3+)
2. zinc (ZN2+)
3. calcium (CA2+)
4. copper(II) (CU2+)
5. iron(II) (Fe2+)
6. iron(III) (Fe3+)
7. ammonium (NH4+)

Question 2

what tests do you do for cations?

Answer 2

• aqueous sodium hydroxide (NaOH)
• aqueous ammonia (NH4OH)

Question 3

aluminium + aqueous sodium hydroxide?

Answer 3

• white ppt
• soluble in excess to form colourless solution

Question 4

aluminium + aqueous ammonia?

Answer 4

• white ppt
• insoluble in excess

Question 5

zinc + aqueous sodium hydroxide?

Answer 5

• white ppt
• soluble in excess to form colourless solution

Question 6

zinc + aqueous ammonia?

Answer 6

• white ppt
• soluble in excess to form colourless solution

Question 7

calcium + aqueous sodium hydroxide?

Answer 7

• white ppt
• insoluble in excess

Question 8

calcium + aqueous ammonia?

Answer 8

not applicable

Question 9

copper(II) + aqueous sodium hydroxide?

Answer 9

• blue ppt
• insoluble in excess

Question 10

copper(II) + aqueous ammonia?

Answer 10

• blue ppt
• soluble in excess to form dark blue solution

Question 11

iron(II) + aqueous sodium hydroxide?

Answer 11

• green ppt
• insoluble in excess

Question 12

iron(II) + aqueous ammonia?

Answer 12

• green ppt
• insoluble in excess

Question 13

iron(III) + aqueous sodium hydroxide?

Answer 13

• red-brown ppt
• insoluble in excess

Question 14

iron(III) + aqueous ammonia?

Answer 14

• red-brown ppt
• insoluble in excess

Question 15

ammonium + aqueous sodium hydroxide?

Answer 15

• no ppt
• on warming, pungent and colourless gas produced, turns damp red litmus paper blue (alkaline)

Question 16

ammonium + aqueous ammonia?

Answer 16

not applicable

Question 17

what are the 5 anions?

Answer 17

1. carbonate (CO3 2-)
2. sulfate (SO4 2-)
3. chloride (Cl-)
4. iodide (I-)
5. nitrate (NO3-)

Question 18

how to test for carbonate?

Answer 18

1. add any dilute acid
   carbonate + acid → salt + CO2 + H2O

Question 19

if carbonate present, what are the test observations?

Answer 19

• effervescence of a colourless & odourless gas produced
• gas turns limewater cloudy, forms white ppt

Question 20

how to test for sulfate?

Answer 20

1. add dilute nitric acid
2. add aqueous barium nitrate

Question 21

what if sulfate is present?

Answer 21

• white ppt formed

Question 22

how to test for chloride?

Answer 22

1. add dilute nitric acid
2. add aqueous silver nitrate

Question 23

how to test for chloride?

Answer 23

1. add dilute nitric acid
2. add aqueous silver nitrate

Question 24

what if chloride is present?

Answer 24

• white ppt formed

Question 25

how to test for iodide?

Answer 25

1. add dilute nitric acid 2. add aqueous silver nitrate

Question 26

what if iodide is present?

Answer 26

- yellow ppt formed

Question 27

how to test for nitrate?

Answer 27

1. add aqueous sodium hydroxide 2. add a small piece of aluminium foil 3. warm the mixture

Question 28

what if nitrate is present?

Answer 28

- effervescence of a colourless & pungent gas produced - gas turns damp red litmus paper blue - aluminium foil dissolves

Question 29

what are the 6 gases?

Answer 29

1. carbon dioxide (CO2) 2. ammonia (NH3) 3. hydrogen (H2) 4. oxygen (O2) 5. sulfur dioxide (SO2) 6. chlorine (Cl2)

Question 30

what is the colour of carbon dioxide?

Answer 30

colourless

Question 31

what is the colour of ammonia?

Answer 31

colourless

Question 32

what is the colour of hydrogen?

Answer 32

colourless

Question 33

what is the colour of oxygen?

Answer 33

colourless

Question 34

what is the colour of sulfur dioxide?

Answer 34

colourless

Question 35

what is the colour of chlorine?

Answer 35

yellow-green

Question 36

which gases are pungent?

Answer 36

ammonia, sulfur dioxide, chlorine

Question 37

how to test for carbon dioxide?

Answer 37

- limewater - forms white ppt

Question 38

how to test for ammonia?

Answer 38

- turns damp red litmus paper blue (alkaline, ammonia is the only alkaline gas)

Question 39

how to test for hydrogen?

Answer 39

- extinguishes a lighted splint with a ‘pop’ sound

Question 40

how to test for oxygen?

Answer 40

- relights a glowing splint

Question 41

how to test for sulfur dioxide?

Answer 41

- turns aqueous acidified potassium manganate (VII) from purple to colourless

Question 42

how to test for chlorine?

Answer 42

- turns damp blue litmus paper red, then bleaches it

Question 43

how to test for chlorine?

Answer 43

- turns damp blue litmus paper red, then bleaches it