TEST OF PRACTICAL KNOWLEDGE QUESTION Credit will be given for strict adherence to the instructions, for observations precisely recorded, and for accurate in...
Credit will be given for strict adherence to the 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 inorganic salts. X is a solution of an inorganic compound. Carry out the following exercises on C, D and X. Record your observations and identity any gas(es) involved. State the conclusion drawn from the result or each test.
(a)(i) Add about 5 cm\(_3\) of distilled water to C in a test tube and shake thoroughly, Divide the resulting solution into two portions.
(ii) Put about 2cm\(^3\) of X into a separate test tube and add the first portion of solution in (a)(i) To the second portion of the resulting solution in (a)(i), add few drops of BaCl\(_{2(aq)}\) followed by excess dil. HCI.
(b) Add about 10 cm of distilled water to D in a boiling tube and shake thoroughly.
(i) To about 2 cm\(^3\) portion of the resulting solution in a test tube, add NaOH\(_{(aq)}\) in drops and then in excess
(ii) To another 2 cm\(^3\) portion of the resulting solution add few drops of K\(_2\)CrO\(_{4(aq)}\)
Tests on C and D and the solution X
Test
Observation
Inference
(a)(i) C + about 5 cm3 distilled water, shake; divide into two
C dissolves to give a colourless solution
C is a soluble salt
(a)(ii) first portion + X
X is decolourised (purple fades to colourless)
C is a reducing agent; it reduces X
second portion + BaCl2(aq) then excess dilute HCl
A white precipitate forms which then dissolves in the excess dilute HCl
Because the precipitate dissolves in acid it is not a sulphate; the sulphite ion, SO32-, is confirmed in C
(b)(i) D + water, then NaOH(aq) dropwise and in excess
A white precipitate forms which dissolves in excess NaOH
Pb2+ (or Al3+/Zn2+); confirmed as Pb2+ by the next test
(b)(ii) D + K2CrO4(aq)
A yellow precipitate forms
Pb2+ confirmed (lead chromate)
Conclusion: C is a soluble sulphite salt and acts as a reducing agent; D is a lead(II) salt; X is a purple oxidising solution that C reduces.
