How many liters of pure water must be added to 30 liters of a 40% acid disinfectant solution to dilute it to a 25% acid solution?
Answer and explanation
Correct answer: A. 18 liters
- Step 1: Amount of pure acid = 30 0.40 = 12 liters. Step 2. Let x be liters of water added. Total volume = 30 + x. Step 3. Set up concentration equation: 12 / (30 + x) = 0.25 = 1/4. Step 4. Cross-multiply: 48 = 30 + x => x = 18 liters. Answer: 18 liters, keeping the 12 liters of pure acid constant in 12 / (30 + x) = 0.25. Why not the others:* 15 liters gives 12/45 = 26.67%; 20 liters gives 12/50 = 24%.
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