Aluminium sulphate and copper sulphate solutions were taken in two test tubes I and II respectively. A few pieces of iron filings were then added to both solutions. The four students A, B, C and D recorded their observations in the form of a table as given below:
Which student has recorded the correct observation?- D
- C
- B
- A
| Student | Al2(SO4)3 solution (I) | CuSO4 solution (II) |
|---|
| A | Colourless solution -> Light green | Blue colour is retained |
| B | Colourless solution -> No change | Blue colour solution -> Green |
| C | Colourless solution -> Light blue | Blue colour solution -> Green |
| D | No change in colour | Blue colour of solution fade. |
"
Correct answer: (c) B
Explanation: Test-tube I, iron filling is added in aluminium sulphate solution, no colour change will be observed as iron is less reactive than aluminium, so it cannot displace aluminium from its sulphate solution. Hence, no reaction takes place.
Test-tube II, iron filling is added in copper sulphate solution, blue colour changes to light green. As iron is more reactive than copper, hence it displaces aluminium from its sulphate solution.
The chemical equation for the reaction is given below:
$3Fe (s) + Al_2(SO_4)_3 (aq) → 3FeSO_4 (aq) + 2Al (s)$
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