The pharmacy receives a prescription for 50 grams of 5% salicylic acid ointment. the pharmacy has a 30% salicylic acid ointment and petrolatum available. using only these products, how much petrolatum should be used to compound the prescription? express the answer in grams. (answer must be numeric; no units or commas; include leading zero when answer is less than 1; round the final answer to the nearest one decimal place.)

ANSWERS

2016-04-10 11:12:26

In this problem, we can formulate two equations. First, the overall mass balance of the ointment. The mass of 30% salicylic acid ointment plus the mass of petrolatum must be 50 grams. x + p = 50 Where x is the mass of 30% salicylic acid ointment and p is the mass of petrolatum Second, the component mass balance of salicylic acid: 0.3 * x = 50 * 0.05 x = 8.33 g Therefore the mass of petrolatum to be used is: x + p = 50 p = 50 – x p = 50 – 8.33 p = 41.67 g Answer: 41.7

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