Identification of ions & gases

Question 1

Zn2+ with NaOH

Answer 1

white precipitate
- dissolves in excess to give a clear colourless solution

Question 2

Zn2+ with NH3

Answer 2

white precipitate
- dissolves in excess to give a clear colourless solution

Question 3

Al3+ with NaOH

Answer 3

white precipitate
- dissolves in excess to give a clear colourless solution

Question 4

Al3+ with NH3

Answer 4

white precipitate formed
- insoluble in excess

Question 5

Ca2+ with NaOH

Answer 5

white precipitate formed
- insoluble in excess

Question 6

Ca2+ with NH3

Answer 6

no apparent change

Question 7

NH4+ with NaOH

Answer 7

no apparent change
- NH3 gas evolved on warming

Question 8

Cr3+ with NaOH

Answer 8

green precipitate
- soluble in excess to give green solution

Question 9

Cr3+ with NH3

Answer 9

green precipitate
- insoluble in excess

Question 10

Cu2+ with NaOH

Answer 10

light blue precipitate
- insoluble in excess

Question 11

Cu2+ in NH3

Answer 11

light blue precipitate
- dissolves in excess to give a deep blue solution

Question 12

Fe2+ with NaOH

Answer 12

green precipitate
- insoluble in excess

Question 13

Fe2+ with NH3

Answer 13

green precipitate
- insoluble in excess

Question 14

Fe3+ with NaOH

Answer 14

reddish brown precipitate
- insoluble in excess

Question 15

Fe3+ with NH3

Answer 15

reddish brown precipitate
- insoluble in excess

Question 16

Carbonate

Answer 16

add dilute HCl
- effervescence occurs & colourless gas is evolved turning limewater milky
-> gas is CO2

Question 17

Nitrate

Answer 17

add NaOH followed by a pinch of Al powder, warm carefully
- pungent gas evolved turning damp red litmus paper blue
-> gas is NH3

Question 18

Sulfate

Answer 18

add dilute HNO3 followed by Ba(NO3)2(aq)
- no change on addition of HNO3
- white precipitate of BaSO4 formed

Question 19

Cl-
I-
Br-

Answer 19

add dilute HNO3 followed by AgNO3
- white precipitate of AgCl
- cream precipitate of AgBr
- yellow precipitate of AgI

Question 20

I-

Answer 20

add dilute HNO3 followed by Pb(NO3)2(aq)
- yellow precipitate of PbI is formed

Question 21

Sulfite

Answer 21

add small volume of dilute HCl
- colourless gas with irritating smell is evolved
- decolourises acidified KMnO4 from purple -> colourless

Question 22

Flame test for cations

Answer 22

• Li+ : red
• Na+ : yellow
• K+ : lilac
• Ca2+ : orange-red
• Ba2+ : apple green / light green
• Cu2+ : bluish green

Question 23

H2 test

Answer 23

• apply lighted splint
• burns with a pop sound

Question 24

O2 test

Answer 24

• apply glowing splint
• relights glowing splint

Question 25

CO2 test

Answer 25

• pass through limewater
• turns limewater milky

Question 26

NH3

Answer 26

• apply damp red litmus paper
• litmus paper turns blue

Question 27

Cl2

Answer 27

• apply damp blue litmus paper
• litmus paper turns red

Question 28

SO2

Answer 28

• pass through acidified K2CR2O7
• acidified K2CR2O7 changes from orange -> green

Question 29

Ethene test

Answer 29

• pass through aqueous bromine
• decolourises aqueous bromine from reddish brown -> colourless