To prepare 30g of salicylic acid at a concentration of 40% in petrolatum, how many grams of salicylic acid will be needed?

To determine how many grams of salicylic acid are needed to prepare a 40% concentration in a total of 30 grams of petrolatum, we begin by understanding what a 40% concentration means in this context. A 40% concentration indicates that 40 grams of the active ingredient (salicylic acid) are present in every 100 grams of the final mixture.

To find out how many grams of salicylic acid are needed in a total of 30 grams at a 40% concentration, we can set up a simple calculation.

First, we need to calculate how much salicylic acid corresponds to 40% of 30 grams:

Salicylic acid needed = Total amount of mixture × Concentration

= 30g × 0.40

= 12g.

This calculation indicates that 12 grams of salicylic acid must be utilized to achieve a 40% concentration in the total of 30 grams of petrolatum. Therefore, the answer of 12 grams is correct because it accurately reflects the calculation based on the defined percentage concentration in the solution.