QA

Question 1

Possible white solid

Answer 1

• compounds of group 1 and 2 metals
• Zn2+/NH4+ compounds

Question 2

Colourless solution

Answer 2

solutions of salts of group 1 and 2 metals, Zn2+/NH4+ salts, dilute acids/alkalis, hydrogen peroxide solution

Question 3

Blue solid/solution

Answer 3

(Solution of) Hydrated Cu2+ salts

Question 4

Green solid

Answer 4

Fe2+ salts(pale green), CuCO3

Question 5

Green solution

Answer 5

Solution of Fe2+ salts(pale green)

Question 6

Yellow solid

Answer 6

Fe3+ salts, AgI(pale yellow), PbI2(bright yellow), ZnO(hot)

Question 7

Yellow solution

Answer 7

Dilute solution of Fe3+ salts

Question 8

Brown/Red-brown solid

Answer 8

Fe2O3, Fe(OH)3, Cu(can be pink)

Question 9

Brown solution

Answer 9

Concentrated solution of Fe3+ salts, i2(aqueous iodine)

Question 10

Purple solid/solution

Answer 10

KMnO4

Question 11

Grey solids

Answer 11

Metals except Cu and Au

Question 12

Black solids

Answer 12

CuO, MnO2, I2(s), carbon powder

Question 13

Solubility of (SO4)2- salts

Answer 13

All soluble except Ba, Ca, Pb, Ag(sparingly soluble)

Question 14

Solubility of chloride salts

Answer 14

Soluble except Ag and Pb(except in hot water)

Question 15

Solubility of carbonate salts

Answer 15

Insoluble except carbonates of group 1 metals and ammonium

Question 16

Solubility of hydroxides and oxides

Answer 16

All insoluble except group 1 metals, Ba and Ca(slightly)

Question 17

Test for hydrogen

Answer 17

Colourless, odourless gas evolved extinguishes lighted splint with ‘pop’ sound

Question 18

Test for oxygen

Answer 18

Colourless, odourless gas relights a glowing splint

Question 19

Test for carbon dioxide

Answer 19

Colourless, odourless gas evolved forms white precipitate with limewater

Question 20

Test for ammonia

Answer 20

Colourless, pungent gas turns damp red litmus paper blue

Question 21

Test for chlorine

Answer 21

Greenish-yellow, pungent gas turns damp blue litmus paper red, then bleaches it

Question 22

Explanation for test for chlorine(blue litmus turns red then bleach)

Answer 22

Chlorine reacts with water to form mixture of hydrochloric acid and hypochlorous acid. The acids turn damp blue litmus paper red. Hypochlorous acid bleaches the litmus paper

Question 23

Test for sulfur dioxide

Answer 23

(Use filter paper soaked with KMnO4) Colourless, pungent gas turns acidified potassium manganate(VII) from purple to colourless.

Question 24

Explanation for sulfur dioxide test

Answer 24

Sulfur dioxide is a reducing agent. It reduces purple manganate(VII) ion to colourless manganese(II) ion

Question 25

Test for ammonium

Answer 25

NaOH-> colourless, pungent gas evolved, (insert test for NH3)

Question 26

Test for Ca2+

Answer 26

NaOH -> white ppt, insoluble in excess Ammonia -> NIL

Question 27

Test for Al3+

Answer 27

NaOH: white ppt, excess>colourless NH3: white ppt, insoluble excess

Question 28

Test for Pb2+

Answer 28

NaOH: white ppt, excess>colourless NH3: white ppt, insoluble excess

Question 29

Test for Zn2+

Answer 29

NaOH: white ppt, excess>colourless NH3: white ppt, excess>colourless

Question 30

Test for Cu2+

Answer 30

NaOH: blue ppt, insoluble excess NH3: blue ppt, excess>dark blue

Question 31

Test for Fe2+

Answer 31

NaOH: green ppt, insoluble excess NH3: Green ppt, insoluble excess ^ppt turns red brown upon standing

Question 32

Test for Fe3+

Answer 32

NaOH: red-brown ppt, insoluble excess NH3: red-brown ppt, insoluble excess

Question 33

Why no visible change if solution contains Na+ or K+

Answer 33

No reaction between aqueous NaOH or aqueous NH3 and solution containing Na+ or K+

Question 34

Why do some precipitates dissolve in excess aqueous sodium hydroxide

Answer 34

Ppts can react further with excess alkali to form complex salt that is soluble. White ppts, Al(OH), Pb(OH)2, Zn(OH)2 are amphoteric oxides and ppt further reacts with aqueous sodium hydroxide to form soluble complex salts

Question 35

Why do some precipitates dissolve in excess aqueous ammonia

Answer 35

Ppts can react further with excess alkali to form complex salt that is soluble. White ppt Zn(OH)2 and blue ppt Cu(OH)2 react with aqueous ammonia to form soluble complex salts

Question 36

Why ammonia gas produced when aqueous sodium hydroxide is added to a solution with NH4+?

Answer 36

Ammonium salts react with aqueous sodium hydroxide to form soluble salt, water and ammonia gas

Question 37

Why cant aqueous ammonia be used to test for NH4+

Answer 37

Upon heating, aqueous ammonia itself will produce ammonia gas. In this case, production of ammonia cannot be used to confirm presence of NH4+ in solution

Question 38

How to differentiate solutions containing Pb2+ and Al3+

Answer 38

Add aqueous solution containing iodide ions/chloride ions/ sulfate ions. Pb+I: bright yellow, Pb+Cl: white, Pb+SO4:white, Ag+any, no visible change

Question 39

Test for carbonate

Answer 39

Add dilute acids, observation and test for CO2

Question 40

Test for sulfate

Answer 40

Add dilute nitric acid followed by aqueous barium nitrate. White ppt is seen

Question 41

Test for chloride

Answer 41

Add dilute nitric acid followed by aqueous silver nitrate. White ppt is seen

Question 42

Test for iodide

Answer 42

Add dilute nitric acid followed by aqueous silver nitrate. Pale yellow ppt is seen

Question 43

Test for nitrate

Answer 43

Add aqueous sodium hydroxide followed by aluminium foil and warm. Test gas evolved with damp red litmus paper. (insert observation for ammonia)

Question 44

Purpose of adding dilute nitric acid before adding test reagent

Answer 44

To remove carbonate ion which may be present in unknown solution as carbonate ion will also react with test reagent to form precipitate

Question 45

Define thermal decomposition

Answer 45

A chemical process which heat is used to break down a single compound into two or more compounds or elements. A gas is usually produced in the process.