Test for ions and radicals Flashcards
The clock glasses shown contained pure samples of (flame test) salts. Describe how the student could have distinguished between the samples that contained potassium ions and those that contained sodium ions using the flame test technique.
- Introduce salt into the flame of the Bunsen burner using a nichrome wire.
- Sodium gives an orange flame.
- Potassium gives a lilac flame.
Which of the substances : , was identified by the addition of silver nitrate, AgNo₃, solution? What observation indicated a positive test result?
Substances : KCl / potassium chloride
Observation : A white precipitate soluble in the ammonia solution.
One of the samples gave a brown ring when a little concentrated sulfuric acid was carefully poured down the inside of a slanting test tube which contained a solution of the salt, together with another reagent. What was the other reagent? Which salt was identifiable by the appearance of a brown ring?
Other reagent : Iron (II) sulfate
Which salt : KNO₃ / Potassium nitrate
Describe how you would test the samples for the presence of the phosphate anion.
To salt solution add ammonium molybdate solution and a few drops of concentrated nitric acid and warm gently. A yellow precipitate is formed.
Having completed the tests, the student should have positively identified three of the salts. A solution of barium chloride, BaCl₂, was then added to solutions of each of the three remaining samples in turn. A white precipitate was produced in two cases Write a balanced equation for either one of the two reactions that occurred.
Na₂SO₃(.7H₂O) + BaCl2 → BaSO3 + 2NaCl (+7H2O)
The student then added dilute hydrochloric acid to the precipitates. What would the student have observed and what conclusion should have been drawn regarding the identities of the two salts?
ppt dissolved - Na₂SO₃.7H₂O (Na₂SO₃, SO₃2-, sulfite)
ppt undissolved - Na₂SO₄.10H₂O (Na₂SO₄, SO₄2-, sulfate)
The student was able to identify the last salt by a process of elimination. Suggest a way of confirming the identity of this salt.
Add dilute acid, gas turns limewater milky.
How could the presence of sulfite ions in aqueous solution be detected?
A white precipitate with barium chloride solution with dissolves in dilute hydrochloric acid.
How would you confirm the presence of the sulfite ion in aqueous solution?
Add barium chloride solution, a white precipitate dissolves in dilute hydrochloric acid.
Nitric acid and its salts contain the nitrate ion (NO₃-). Describe in detail how you could test for the presence of the nitrate anion in aqueous solution.
- Add freshly-prepared iron (II) sulfate solution.
- Trickle concentrated sulfuric acid dropwise down the side of the test-tube.
- A brown ring forms at junction of the two liquids.
Describe a test for the presence of chloride ion (Cl-) in water.
- Add silver nitrate and dilute nitric acid.
- A white precipitate forms.
