Adding 300 g water to 200 g of 25% brine

There are 200 g of brine at 25% concentration. After 300 g of water is added, the total becomes 500 g. What is the concentration of the diluted brine?

Step-by-step

1. 25% × 200 = 50
   Mass of solute (unchanged by adding water or evaporating)
2. 50 ÷ 500 = 10%
   Solute ÷ new total solution = new concentration

Why it works

Adding water increases the total mass but leaves the amount of salt unchanged, so the new concentration is the same salt divided by the larger total mass.

Common mistakes

• Dividing the salt by the original 200 g instead of the new total.
• Subtracting the water from the concentration.

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