Tests for ions 3.1.4

Question 1

CO₃²⁻ (carbonate ion)

Answer 1

reaction with dilute nitric acid forming CO₂(g)

bubble through limewater (Ca(OH)₂) to form white ppt of CaCO₃ which turns it cloudy

Question 2

SO₄²⁻ (sulfate ion)

Answer 2

precipitation with Ba²⁺(aq) to form white precipitate of barium sulfate

add barium nitrate not chloride as this would introduce Cl⁻ that would disrupt later halide test

Question 3

Cl⁻, Br⁻, I⁻

the precipitation reactions, including ionic equations, of the aqueous anions Cl –, Br– and
I– with aqueous silver ions, followed by , and their use as a test for different halide ions.

Answer 3

add aq AgNO₃
AgCl - white ppt
AgBr - cream ppt
AgI - yellow ppt

then add aqueous ammonia,
AgCl - soluble in dilute NH₃
AgBr - soluble in conc NH₃
AgI - insoluble in conc NH₃

Question 4

NH₄⁺

Answer 4

reaction with warm NaOH(aq) forming NH₃(g)

Test w/ moist indicator paper which should go BLUE

Question 5

Sequence of tests required and why

Answer 5

carbonate
sulfate
halide

(BaCO₃ and Ag₂SO₄ are both insoluble.)

Question 6

Reactivity … down the halogens

Answer 6

decreases

Question 7

colour change when Cl₂ is added to a Br⁻ solution
in water
in cyclohexane

Answer 7

Br₂ forms
Orange in water
Orange in cyclohexane

Question 8

colour change when Cl₂ is added to a I⁻ solution
in water
in cyclohexane

Answer 8

I₂ forms
Brown in water
Purple in cyclohexane

Question 9

colour change when Br₂ is added to a Br⁻ solution
in water
in cyclohexane

Answer 9

I₂ forms
Brown in water
Purple in cyclohexane

Question 10

colour of Cl₂ in water and cyclohexane

Answer 10

pale green

Question 11

colour of Br₂ in water and cyclohexane

Answer 11

orange

Question 12

colour of I₂ in water and cyclohexane

Answer 12

brown in water

purple in cyclohexane