Ion Tests

Question 1

What is the test for Carbonates (CO₃²⁻) and what is the result if present?

Answer 1

• Add dilute HCl (or other acid).
• If carbonates are present, CO₂ is released.

The gas can be bubbled through limewater which will turn cloudy in the presence of CO₂.

Question 2

What is the test for Sulfates (CO₃²⁻) and what is the result if present?

Answer 2

• Add dilute HCl (or other acid) and Barium Chloride, BaCl₂.
• Barium Sulfate is insoluble, so if there are sulfates present, a white precipitate (Barium Sulfate) will form.

Question 3

What is the test for Ammonia Gas and what is the result if present? Also why must the paper be damp?

Answer 3

For Ammonia gas (NH₃) use a damp piece of red Litmus paper. It will turn blue if present since Ammonia gas is alkaline.

It must be damp so the Ammonia gas can dissolve.

Question 4

What is the test for Ammonia Ions and what is the result if present?

Answer 4

Add NaOH and warm the mixture. If Ammonium ions are present, Ammonia is given off.

Question 5

What is the test for Halides and what is the result if: Cl, Br and I are present?

Answer 5

• Add dilute Nitric Acid to remove interfering ions.
• Add Silver Nitrate Solution (AgNO₃).

Chloride, Cl⁻: White Precipitate.
Bromide, Br⁻: Cream Precipitate.
Iodide, I⁻: Yellow Precipitate.

Question 6

What chemical can be added to the Halide test to further check the results and what are the outcomes?

Answer 6

Ammonia solution can be added. Each silver halide has a different solubility (Larger ion = harder to dissolve).

Chloride: Dissolves in dilute NH₃
Bromide: Dissolves in concentrated NH₃
Iodide: Does not dissolve in dilute NH₃

Question 7

What is the equation for a Halide test?

Answer 7

Ag⁺ + X⁻ → AgX (X = Cl, Br or I)

Question 8

What is the equation for a Carbonate test? Give an example with Calcium Carbonate and HCl:

Answer 8

CO₃²⁻ + 2H⁺ → CO₂ + H₂O

eg: CaCO₃ + HCl → CO₂ + H₂O + CaCl₂

Question 9

What is the equation for a Sulfate test? Give an example with Sodium Sulfate and Barium Chloride:

Answer 9

Ba²⁺ + SO₄²⁻ → BaSO₄

eg: BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl

Question 10

What order should these tests be done in?

Answer 10

1) Test for Carbonates
2) Test for Sulfates
3) Test for Halides

Question 11

What precaution should be taken with the acid?

Answer 11

The acid selected mustn’t interfere with the test. (Don’t use HCl with Chloride ions).