A blue solid was given to a student who suggested, from its colour only, that it was copper(II) sulfate. Another student suggested that it was copper(II) hydroxide, which is also blue. The students proposed some tests to distinguish between these two blue solids.

Give the expected observations for copper(II) sulfate and copper(II) hydroxide.

A flame test was carried out on the blue solid, but the flame colour observed was not that expected for a blue solid containing copper(II) ions.

Therefore another student suggested that the blue solid could be anhydrous cobalt(II) chloride.

Cobalt(II) chloride can be distinguished from copper(II) sulfate and copper(II) hydroxide by testing for the anion. Describe a suitable test for the chloride ion, including the positive result.

The inorganic compounds A, B and C each contain one cation and one anion.

A is a green solid. 

Two tests were carried out on separate portions of an aqueous solution of A:

• Test 1: A green precipitate formed when a few drops of NaOH_(aq) were added to a sample of the solution of A. Upon addition of excess NaOH(aq), the precipitate dissolved to form a green solution.
• Test 2: A white precipitate formed when dilute HNO_3(aq) and AgNO_3(aq) were added to a sample of the solution of A.

Give the formulae of the cation and anion in A.

Give the formula of the anion responsible for the green colour of the final solution in test 1. 

Write the ionic equation for the reaction in test 2. Include state symbols.

B is a pale pink solid.

Two tests were carried out on separate portions of an aqueous solution of B:

• Test 1: A light-brown precipitate formed when when NaOH_(aq) was added to a sample of the solution of B. The precipitate darkened on standing in air.
• Test 2: A white precipitate formed when dilute HNO_3(aq) and BaCl_2(aq) were added to a sample of the solution of B.

Give the formulae of the cation and anion in B.

Identify the precipitate formed in test 1, and explain why it darkens.

Write the ionic equation for the reaction in test 2. Include state symbols.

A compound of a d-block element is dissolved in water to form a solution X.

A series of tests is carried out on separate 1 cm³ portions of solution X.

Complete the table.

Sulfur dioxide is passed through a sample of solution X. A redox reaction occurs in which the sulfur dioxide forms sulfate ions.

The solution Y which forms is no longer yellow-brown.

Excess dilute aqueous ammonia was added to a 1 cm³ solution of Y in a test tube. A precipitate is observed.

State the colour and formula of the precipitate.

State the formula of the cation in solution Y.

The mixture from part b) was left to stand for a few minutes. The surface of the precipitate turned brown.

State the formuala of the brown compound.

Complete the ionic equation for the reaction between the cation in solution X and sulfur dioxide to form solution Y.

State symbols are not required.

..........  +  SO₂  +  2H₂O  ➔  ..........  + SO₄^2-  +  ..........