How many kg of pure acid must be added to 200 g of a 30% acid solution to obtain a 75% solution.

To solve the problem, first we find the amount of pure water in a 30% solution weighing 200 grams.
To do this, we first find the total weight of the acid in the solution.
200 * 0.3 = 60 grams.
In this case, the total weight of the water is:
200 – 60 = 140 grams.

The amount of water in the new solution.
100% – 75% = 25%.

Since we will add pure acid, and there is no water in its composition, we find the total weight of the solution that should be obtained when adding.

140 / 0.25 = 560 grams.

We find the required weight of the acid.
560 – 200 = 300 grams.

We convert grams to kilograms.
300/1000 = 0.3 kg.

Answer.
0.3 kg of pure acid.