3.1.4 Testing For Ions

Question 1

Definition of Anions

Answer 1

Negative ions: Carbonate ions (CO3^2-), Sulfate ions (SO4^2-), Halide ions (Cl, BR, I,)

Question 2

What do carbonate ions (CO3^2) react with?

Answer 2

Acid

Question 3

Method for testing CO3^2-

Answer 3

> Add dilute strong acid

> Collect any gas formed and pass it through limewater

Question 4

Positive test observations for CO3^2-

Answer 4

> Fizzing/ Bubbling
Colourless gas produced
Gas turns limewater cloudy

Question 5

What do carbonate ions (SO4^2) react with?

Answer 5

Barium ions

Question 6

Method for testing SO4^2

Answer 6

> Add dilute HCL acid and Barium chloride

Question 7

Positive test observations for SO4^2-

Answer 7

A white precipitate is formed

Question 8

Equation for sulfate ions

Answer 8

Ba^2 (AQ) + SO4^2- (AQ) –> BASO4 (AQ)

Question 9

What do Halide ions (Cl, Br, I) react with?

Answer 9

Silver

Question 10

Method for testing for hallide ions

Answer 10

Dissolve halide ions in water and add aqueous solution of silver nitrate
if colour hard to distinguish, ass aqueous ammonia (first dilute, then concentrated)

Question 11

Positive test observations for Halide ions

Answer 11

AgCl - White precipitate, soluble in dilute Nh3
AgBr - Cream precipitate, soluble in conc NH3
AgI - Yellow precipitate, insoluble in NH3

Question 12

Definitions of cations

Answer 12

Positive ions ( often containing metal ions)

Question 13

What does Ammonium ions (NH4+) react with?

Answer 13

Hydroxide ions

Question 14

Equation for testing for ammonium ions

Answer 14

NH4+ (AQ) + OH-(AQ) –> NH3 (AQ) + H2O (AQ)

Question 15

Method for testing for ammonium ions (NH4+)

Answer 15

> Add sodium hydroxide solution and warm gently , then test any gas evolved with red litmus paper

Question 16

Positive test observations for ammonium ions (NH4+)

Answer 16

NH4+ will turn red litmus paper blue and also will have a strong smell