C and D are samples of two different simple salts. Carry out the following exercises on them. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test.
a) Heat about one-half of C in a dry test tube until no further change is observed. Allow to cool.
(b)(i) To the cooled residue from (a) above, add about 5cm\(^3\) of dilute hydrochloric acid and warm.
(ii) To about 2cm\(^3\) of the clear solution from (b)(i) above add aqueous ammonia in drops until it is in excess.
(c) Put all of D in a boiling tube and add about 10cm\(^3\) of distilled water. Shake thoroughly and divide into two portions.
(d)(i) To the first portion from (c) above, add about 2cm\(^3\) of barium chloride solution, followed by dilute hydrochloric acid in excess. Warm the mixture.
(ii) To the second portion from (c) above, add 2 or 3 of acidified potassium tetraoxomanganate (VII) solution and shake.
Explanation
| Test | Observation | Inference |
| C + heat |
Colourless, odourless gas evolved which turned lime water milky Green colour of C turned black |
Gas is CO\(_2\) from CO\(_{3}^{2-}\) or HCO\(_3\) Cu\(^{2+}\) present |
| (b)(i) Black residue + dil. HCl + Heat | Residue dissolved to give a blue solution | Cu\(^{2+}\) present |
| (ii) Solution from (b)(i) + aqueous NH\(_3\) in drops then in excess | Pale blue ppt. soluble in excess to give a deep blue solution | Cu\(^{2+}\) present |
| (c) D + water | D dissolved forming a colourless solution |
D is a soluble salt |
| (d)(i) Soln. from (c) + aqueous BaCl\(_2\)n+ dil. HCl + Heat |
White ppt. formed ppt. dissolved forming a colourless soln. colourless gas with irritating smell evolved; the gas turned the colour of acidified K\(_2\)Cr\(_2\)O\(_7\) soln. from orange to green |
SO\(_3\) or SO\(_4^{2-}\) CO\(_3^{2-}\) or S\(^{2-}\) present SO\(_2\) from SO\(_3^{2-}\) |
| (ii) Soln. from (L) + acidified KMnO\(_4\) soln. | The purple colour KMnO\(_4\) soln. decolourised | Reducing agent present |