Exercise 5.1
Which of the following mixtures are correctly classified as homogeneous (Hm) and heterogeneous (Ht)? Choose the correct option. (i) Air — Hm, Milk — Ht, Sugar solution — Hm, Smoke — Hm (ii) Brass — Ht, Fog — Ht, Vinegar — Ht, Muddy water — Hm (iii) Copper sulfate solution — Hm, Salt solution — Hm, Milk — Hm, Bronze — Hm (iv) Muddy water — Ht, Milk — Ht, Blood — Ht, Brass — Hm
Not cross-checked
NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.
NCERT’s answer
(iv)
Option (iv) is the correct classification.
Muddy water — Ht: a suspension, the mud particles are visible and settle.
Milk — Ht: a colloid, and colloids are heterogeneous mixtures.
Blood — Ht: also a colloid, whose components can be spun apart by centrifugation.
Brass — Hm: an alloy of about $\displaystyle 80$% copper and $\displaystyle 20$% zinc, and an alloy is a homogeneous mixture.
(i) is wrong because smoke, being solid particles suspended in air, is heterogeneous, not Hm.
(ii) is wrong on three counts: brass is Hm, vinegar (acetic acid in water) is a Hm solution, and muddy water is Ht.
(iii) is wrong because milk is a colloid and therefore Ht, not Hm.