Credit will be given for strict adherence to instructions, for observations precisely recorded, and for accurate inferences. All tests, observations, and inferences must be clearly entered in your answer book, in ink at the time they are made.
C and D are samples of two 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) Put all of C in a test tube and heat strongly for about 3 to 5 minutes. Allow the residue to cool.
(b) Add about 5cm\(^3\) of distilled water to the residue from (a) above. Shake and test with litmus paper.
Explanation
| Test | Observation | Inference |
| (a) C + heat |
Colourless, odourless gas turned lime water milky/turbid vapour condenses at the neck of the test tube. White residue is left |
Gas in CO\(_2\) from CO\(_2^{2-}\) or HCO\(_{3-}\) |
| (b) Residue from a + water + litmus | Dissolved to form a colourless solution turned red litmus to blue |
Alkaline solution
|
| (c) D + water | Dissolved to form colourless solution | Pb\(^{2-}\) or Al\(^{3+}\) or Zn\(^{2+}\) or Ca\(^{2+}\) present |
| (i) Soln. of D + NaOH\(_{(aq)}\) | White ppt.; ppt. soluble | pb\(^{2+}\) or Al\(^{3+}\) or Zn\(^{2+}\) |
| (ii) Soln.of D + NH\(_{3(aq)}\) in drops then in excess |
White ppt. ppt. soluble |
pb\(^{2+}\) or Al\(^{3+}\) |
|
(iii) Soln of D + HCl ppt. heated, on cooling |
White ppt. ppt. dissolves/disappears ppt. reappears |
ppt. is PbCl\(_2\) pb\(^{2+}\) present |