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Question:

When 25g of Na2SO4 is dissolved in 103kg of solution, its concentration will be:

2.5 ppm

25 ppm

250 ppm

100 ppm

Solution:

When a solute is present in very minute amounts (trace quantities) the concentration is expressed in ppm.
ppm of A = mass of component A / total mass of solution × 10⁶
= 0.025 / 103 × 10⁶
= 25 ppm