Question

How many grams of salicylic acid should be added to 75 g of a polyethylene glycol ointment to prepare an ointment containing 6% w/w of salicylic acid?

Answer 1

Answer:

4.79 g

Step-by-step explanation:

mass of salicylic acid = ??

Mass of polyethylene = 75 g

% w/w concentration = 6% w/w

Let the mass of  salicylic acid be x

Let the mass of solution = 75 + x

from

% w/w = mass of solute/ mass of solution * 100

Hence concentration of salicylic is;

6 = (x/75 + x) * 100

6/100 = x/75 + x

0.06 (75 + x) = x

4.5 + 0.06x =x

4.5 = x-0.06x

x = 4.5/0.94

x= 4.79 g