4.2

Question 1

4.2 Identifying unknowns (2) STUDENT

• To identify the positive and negative inorganic ions in four solutions, using appropriate apparatus and procedures.

Answer 1

You are given four unknown solutions. Using the chemicals provided you should carry out a series of tests to allow you to identify each solution A–D

Question 2

Solutions A–D

Answer 2

Treat ALL of these as irritant

Question 3

Nitric acid, HNO3(aq), of concentration 1.0 mol dm3

Answer 3

DANGER

Causes severe skin burns and eye damage

Question 4

Silver nitrate, AgNO3(aq), of concentration 0.05 mol dm3

Answer 4

No hazard classification

Can stain the skin

Question 5

Aqueous barium chloride, BaCl2(aq) 0.2 mol dm3

Answer 5

Harmful if swallowed

Question 6

Aqueous sodium hydroxide, NaOH(aq) 0.4 mol dm3

Answer 6

WARNING

Causes skin irritation and serious eye irritation

Question 7

Equipment

Answer 7

• pH indicator paper
• protective gloves
• wash bottle containing distilled (or de-ionised water)
• measuring cylinder (25 cm3)
• beaker (100 cm3)
• glass rod
• conical flask (100 cm3)
• test-tube rack
• four test tubes
• dropping pipettes
• spatula
• bunsen burner
• test-tube holder

Question 8

Health & Safety

Answer 8

• Wear eye protection throughout.

* You are advised to wear chemical-resistant gloves when handling aqueous nitric acid.

Question 9

Procedure

Answer 9

The identities of the solutions A–D are listed below in no particular order:
•	ammonium chloride, NH4Cl (aq)
•	sodium chloride, NaCl (aq)
•	sodium hydroxide , Na2CO3(aq)
•	sodium sulfate, Na2SO4 (aq)

1. Plan and carry out a series of tests that would allow you to identify each solution A–D.
2. You should carry out the minimum number of tests required. Each test should produce a positive result for at least one of the solutions A–D. You can use any of the chemicals supplied.
3. Record the tests you carried out.
4. Record all the observations for your tests on solutions A–D.
5. Record your conclusions for each test.
6. Record the identity of each solution.

Question 10

Extension Opportunities

1. Write the equations for the reactions you have observed.

Answer 10

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Question 11

2. Write the methods for the experiments you have carried out.

Answer 11

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