U2S2 tests for ions

Question 1

Flame test

Answer 1

• group 2 metals
• dip nichrome wire loop in concentrated hydrochloric acid, dip into unknown compound and hold in bunsen burner
• calcium = brick red, strontium = red, barium = pale green

Question 2

Precipitate test

Answer 2

• group 2
  -add dilute sodium hydroxide solution
• magnesium= slight white, white in excess
• calcium and strontium= slight white, slight white
• barium= no change

Question 3

Ammonium ions

Answer 3

• add dilute sodium hydroxide and gently heat mixture
• litmus paper turns blue if present
  NH4+(aq) + OH-(aq) -> NH3(g) + H2O(l)

Question 4

Sulfate ions

Answer 4

• add dilute hydrochloric acid followed by barium chloride solution
• white precipitate forms if present
  Ba(aq)2+ + SO42-(aq) -> BaSO4(s)

Question 5

Hydroxide ions

Answer 5

• dip piece of litmus in solution
• paper turns blue if present

Question 6

Halide ions

Answer 6

• add dilute nitric acid followed by silver nitrate solution
• flouride, no precipitate
• chloride, white, dissolve in dilute ammonia
• bromide, cream, dissolve in concentrated ammonia
• iodide, yellow, won’t dissolve

Question 7

Ionic equation for halide ions and silver nitrate

Answer 7

Ag+(aq) + X-(aq) -> AgX(s)

Question 8

Carbonate ions

Answer 8

• add dilute hydrochloric acid
  CO32-(aq) + 2H+(aq) -> CO2(g) + H2O(l)
• bubble through limewater, turns cloudy

Question 9

Equation for reacting silver halide with ammonia solution

Answer 9

AgX + 2NH3 -> Ag(NH3)2+ + X-