Consider the following statements : I. A solution of iodine in ethanol known as 'tincture of iodine' is a heterogeneous mixture. II. A suspension is a heterogeneous mixture and its particles scatter a beam of light passing through it, making its path visible. III. A colloidal solution, although it appears homogeneous, is a heterogeneous mixture. Which of the statements given above are correct ?
- A.I and II only
- B.II and III only
- C.I and III only
- D.I, II and III
Correct answer
Explanation
The correct answer is B, II and III only. Tincture of iodine is a true solution, which is homogeneous, so statement I is wrong, while II and III are right.
In a true solution such as iodine in alcohol, the solute particles are smaller than 1 nm and spread evenly, so the mixture is uniform throughout and does not scatter light. A suspension has particles larger than about 100 nm that can be seen, settle on standing and scatter light, so the path of a beam becomes visible. A colloid has particles between 1 and 100 nm; it looks uniform but is really heterogeneous and shows the Tyndall effect.
A is wrong because it includes statement I, which calls a true solution heterogeneous.
C is wrong for the same reason and also leaves out the correct statement II.
D is wrong because not all three statements are correct.
Exam tip: true solution is homogeneous; colloid and suspension are heterogeneous, and both scatter light (Tyndall effect).
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