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How much pure methanol should be added to 800 ml of a solution containing 18.75% of methanol to change the concentration of methanol in the mixture to 35%?

How much pure methanol should be added to 800 ml of a solution containing 18.75% of methanol to change the concentration of methanol in the mixture to 35%? Correct Answer 200 ml

Let x ml of methanol is added to 800 ml solution.

Amount of methanol in given solution = 18.75% of 800 = 150 ml

Total quantity of new solution = (800 + x) ml

⇒ 150 + x = 35% of (800 + x)

⇒ 150 + x = (800 + x) × 7/20

⇒ 3000 + 20x = 5600 + 7x

⇒ 13x = 2600

∴ x = 200 ml

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