Chemical tests

Question 1

test for Carbon Dioxide (CO2)

Answer 1

turns limewater milky (sparingly soluble Ca(OH) 2 forms insoluble CaCO3 )

Question 2

Chlorine (Cl2 ) test

Answer 2

bleaches damp litmus paper (Cl2 reacts with water to form HCl and HOCl)

Question 3

Hydrogen (H2 ) test

Answer 3

pops with a lighted splint

Question 4

Oxygen (O2 ) test

Answer 4

relights a glowing splint

Question 5

Carbonate (CO 3 2- ) test

Answer 5

add dilute acid; effervescence, carbon dioxide produced

Question 6

Sulfate (SO4 2- ) test

Answer 6

add dilute nitric acid then aqueous barium chloride. Gives white precipitate

Question 7

Chloride (Cl - ) test

Answer 7

add dilute nitric acid then aqueous silver nitrate. Gives white precipitate. Dissolves in dilute ammonia to give colourless solution (of [Ag(NH 3 ) 2 ] + )

Question 8

Bromide (Br - ) test

Answer 8

add dilute nitric acid then aqueous silver nitrate. Gives cream precipitate. Dissolves in concentrated ammonia but not in dilute ammonia

Question 9

Iodide (I - ) test

Answer 9

add dilute nitric acid then aqueous silver nitrate. Gives yellow precipitate. Does not dissolve in either concentrated or dilute ammonia

Question 10

Iron II (Fe 2+ ) test

Answer 10

add aqueous sodium hydroxide gives green precipitate, insoluble in excess

Question 11

Iron III (Fe 3+ ) test

Answer 11

add aqueous sodium hydroxide gives orange/brown precipitate, insoluble in excess

Question 12

Copper (Cu 2+ ) test

Answer 12

add aqueous sodium hydroxide gives blue precipitate, insoluble in excess. Or add ammonia: gives a blue precipitate which dissolves in excess to give a blue solution

Question 13

Calcium (Ca 2+ ) test

Answer 13

add aqueous sodium hydroxide gives white precipitate, insoluble in excess.

Question 14

Aluminium (Al 3+ ) test

Answer 14

add aqueous sodium hydroxide gives white precipitate which dissolves in excess

Question 15

H + (any acid) test

Answer 15

turns blue litmus red or makes sodium carbonate effervesce (makes CO 2 gas)

Question 16

H2O test

Answer 16

1. turns white anhydrous copper (II) sulphate into blue hydrated copper (II) sulphate. 2. It also turns blue anhydrous cobalt (II) chloride into pink hydrated cobalt (II) chloride reaction is reversible, colour changes reversed when hydrated salts are heated.

Question 17

Test for Unsaturated hydrocarbons

Answer 17

turns bromine water from orange to colourless.

Question 18

Test for aldehydes

Answer 18

produces a silver mirror from a colourless solution of Tollens’ reagent (or produces a red precipitate from blue coloured Fehling’s solution (needs heat))

Question 19

Tests for organic (and other) acids (carboxylic acid)

Answer 19

they release CO2 (bubbles of gas are observed) when shaken with sodium carbonate solution

Question 20

Test for acyl chloride

Answer 20

gives misty fumes with water

Question 21

Test for alcohol

Answer 21

add acidified potassium dichromate (K2Cr2O7) orange to green (Cr3+)

Question 22

Manganate ion change of colour

Answer 22

when reduced, goes from deep purple to colourless

Question 23

Manganate ion change of colour

Answer 23

when reduced, goes from deep purple to colourless

Question 24

test for sulfate ion

Answer 24

add nitric acid (removes carbonate ions so no other ppt forms), add barium chloride, barium sulfate forms, white ppt.

Question 25

test for amines

Answer 25

turns litmus paper blue (naturally basic)

Question 26

test for arene

Answer 26

burn in air. produces smokey flame and soot.