Qualitative Analysis

Question 1

how do you test for an aluminium cation?

Answer 1

aqueous sodium hydroxide: white ppt. formed, soluble in excess to form a colourless solution

aqueous ammonia: white ppt. formed, insoluble in excess

Question 2

how do you test for a zinc cation?

Answer 2

aqueous sodium hydroxide: white ppt. formed, soluble in excess to form a colourless solution

aqueous ammonia: white ppt. formed, soluble in excess to form a colourless solution

Question 3

how do you test for a calcium cation?

Answer 3

aqueous sodium hydroxide: white ppt. formed, insoluble in excess

aqueous ammonia: no ppt. formed

Question 4

how do you test for a copper(II) cation?

Answer 4

aqueous sodium hydroxide: blue ppt. formed, insoluble in excess

aqueous ammonia: blue ppt. formed, soluble in excess to form a dark blue solution

Question 5

how do you test for a iron(II) cation?

Answer 5

aqueous sodium hydroxide/ammonia: green ppt. formed, insoluble in excess

*forms red-brown ppt. when on standing in air as it oxidises

Question 6

how do you test for a iron(III) cation?

Answer 6

aqueous sodium hydroxide/ammonia: red-brown ppt. formed, insoluble in excess

Question 7

how do you test for an ammonium cation?

Answer 7

aqueous sodium hydroxide: no ppt. formed, colourless pungent gas evolves upon heating which turns damp red litmus paper blue

Question 8

how do you test for a carbonate anion?

Answer 8

add any dilute acid; effervescence of a colourless and odourless gas which forms white ppt. in limewater

Question 9

how do you test for a sulfate anion?

Answer 9

add dilute nitric acid and aqueous barium nitrate; white ppt. forms (barium sulfate)

Question 10

how do you test for a chloride anion?

Answer 10

add dilute nitric acid and aqueous silver nitrate; white ppt. forms (silver chloride)

Question 11

how do you test for an iodide anion?

Answer 11

add dilute nitric acid and aqueous silver nitrate; yellow ppt. formed (silver iodide)

Question 12

how do you test for a nitrate anion?

Answer 12

add aqueous sodium hydroxide and a small piece of aluminium foil before warming the mixture; effervescence of a colourless and pungent gas, gas evolved turns damp red litmus paper blue

Question 13

how do you test and identify carbon dioxide?

Answer 13

• colourless, odourless
• bubble into limewater
• white ppt. forms (calcium carbonate)

Question 14

how do you test and identify ammonia gas?

Answer 14

• colourless, pungent
• use damp red litmus paper
• turns the litmus paper blue

Question 15

how do you test and identify hydrogen gas?

Answer 15

• colourless, odourless
• use a lighted splint
• extinguishes lighted splint with a ‘pop’ sound

Question 16

how do you test and identify oxygen gas?

Answer 16

• colourless, odourless
• use a glowing splint
• relights glowing splint

Question 17

how do you test and identify sulfur dioxide?

Answer 17

• colourless, pungent
• use aqueous acidified potassium manganate(VII) on filter paper
• turns from purple to colourless

Question 18

how do you test and identify chlorine gas?

Answer 18

• greenish-yellow, pungent
• use damp blue litmus paper
• turns litmus paper red, then bleaches it