Exp 6.1 D - To detect the presence of nitrate ions in aqueous solution

Question 1

Apparatus required

Answer 1

Test tube, dropper, wash bottle, spatula

Question 2

Chemicals required (4)

Answer 2

Any nitrate salt (NaNO3, KNO3), iron (II) sulfate solution, concentrated sulfuric acid, deionised water

Question 3

Explain the 5 steps required for this experiment

Answer 3

1. Fill a test tube to 1/4 full with a wash bottle of deionised water.
2. Add a small amount of the nitrate salt to the water. Shake to help dissolve. Observe.
3. Add the same quantity of freshly prepared iron (II) sulfate solution to the test tube.
4. Use a dropper to add 3cm^3 of concentrated sulfuric acid down the inside of the test tube. The test tube should be slanted slightly at an angle.
5. Note that a brown ring is formed at the junction of the two layers.

Question 4

Why does a brown ring is formed at the junction of the two layers? (2)

Answer 4

1. The brown ring is formed as a result of nitrate ions being present and hence is the confirmatory test for the presence of the nitrate ion.
2. The brown colour is due to the formation of the substance FESO4.NO.

Question 5

Why must concentrated sulfuric acid be used?

Answer 5

When describing this experiment it is important to phrase concentrated sulfuric acid as the experiment does not work with dilute sulfuric acid.

Question 6

What is the conclusion of this experiment?

Answer 6

Nitrate ions are present in the solution