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How much urea must be dissolved in water to obtain 500 g of a 10% w/w aqueous solution?
A10 g
B50 g
C100 g
D450 g
Answer & Solution
Correct answer: B. 50 g
1. Mass percentage (w/w) = mass of solute / mass of solution x 100.
2. Here 10 = (mass of urea / 500) x 100.
3. Rearranging: mass of urea = (10 x 500) / 100 = 50 g.
4. So 50 g of urea is needed; 450 g is the mass of water, not the solute.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 9 Solutions "Mass percentage", p.139_
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