QA Part II

Question 1

What sort of precipitates dissolve in excess NaOH?

Answer 1

Amphoteric precipitates.

Question 2

What precipitates dissolve in excess aq ammonia?

Answer 2

Zinc and copper (II)

Question 3

What ions do not form a ppt in NaOH and aq. ammonia respectively?

Answer 3

NaOH: NH4+ (ammonium). Produces ammonia gas upon heating.

NH3: NH4+ (ammonium) and Ca2+ (Calcium).

Question 4

How do we differentiate Lead(II) ion from the other amphoteric ions?

Answer 4

Lead(II) chloride and lead(II) sulfate are insoluble (white in colour), so is lead(II) iodide (yellow)

Question 5

How do we differentiate aluminium ion from the other amphoteric ions?

Answer 5

You have to test for the other two ions. If both tests are negative, you have an aluminium ion.

Question 6

How do you differentiate zinc ion from other amphoteric ions?

Answer 6

Use aqueous ammonia. If it dissolves in excess NH3 it is FUNNNY! WHEN THE IMPOSTOr I UsUS!

Question 7

How do we test for carbonate anion? What is the result?

Answer 7

Add dilute hydrochloric/nitric acid. Bubble the gas
produced into limewater.

Effervescence is observed. Gas produced from the reaction will form white precipitate when it reacts with limewater.

Question 8

How do we test for nitrate anion?

Answer 8

Add dilute sodium hydroxide, then add a
piece of aluminium foil and warm. Test the gas produced (ammonium gas) with a piece of moist
red litmus paper. The moist red litmus paper will turn blue.

Question 9

How do we test for sulfate anion?

Answer 9

Add dilute nitric acid, and then aq. barium nitrate (or acidified barium nitrate). White ppt of barium sulfate will form.

Question 10

How do we test for chloride anion?

Answer 10

Add dilute nitric acid to the solution and then add aqueous silver nitrate. White ppt. of silver chloride will form.

Question 11

How do we test for iodide anion?

Answer 11

Add dilute nitric acid to the solution then add aq. silver nitrate –> yellow ppt. of silver iodide is formed.

Question 12

Why do we add dilute nitric acid first in tests for sulfate, chloride and iodide ions?

Answer 12

Dilute nitric acid is is added first to react with any carbonate ions or hydroxide ions present. This is to prevent false positive results as carbonate ions also form precipitates with the reagents.

Question 13

What three compounds can thermal decomposition occur in?

Answer 13

Hydroxides, carbonates, and nitrates.

Question 14

What is thermal decomposition of a compound?

Answer 14

Breaking down a compound by heat alone. N.B. Thermal decomposition is not combustion as combustion requires oxygen.

Question 15

What hydroxides does thermal decomposition occur in? What are their products?

Answer 15

All hydroxides except Group I hydroxides. Water vapour is evolved (e.g. Ca(OH)2 –> CaO + H2O)

Question 16

What carbonates does thermal decomposition occur in? What are the products?

Answer 16

All carbonates except Group I carbonates. Carbon dioxide is evolved.

Question 17

What nitrates can thermal decomposition occur. What products bruh.

Answer 17

All nitrates can thermally decompose. In Group I nitrates, oxygen only is evolved. Otherwise, nitrogen dioxide and oxygen is evolved.

Question 18

Name the substances/ions that are BLACK in colour.

Answer 18

CuO, CuS, CoO, FeO, FeS, PbS, MnO2

Question 19

Name the substances/ions that are BLUE in colour.

Answer 19

[Cu]2+ (aq), CoCl2 (anhydrous)

Question 20

Name the subtances/ions that are GREEN in colour.

Answer 20

[Fe]2+, [Ni]2+, CuCl2 (anhydrous), CuCO3

Question 21

Name the subtances/ions that are REDDISH-BROWN in colour.

Answer 21

[Fe]3+ (solid), Br2 (liquid/aqueous)

Question 22

Name the subtances that are BROWN in colour.

Answer 22

I2 (iodide gas) (aq)

Question 23

Name the subtances/ions that are YELLOW in colour.

Answer 23

[Fe]3+ (aq), PbI2, AgBr, AgI

Question 24

Name the substances/ions that are ORANGE in colour

Answer 24

[Cr2O7]2-, PbO

Question 25

Name the substances that are PINK in colour

Answer 25

CoCl2 (hydrated), Cu (pure metal)

Question 26

Name the substances/ions that are PURPLE in colour

Answer 26

[MnO4]-, I2 (solid//gas)