Approximately how many milliliters of water are needed to pr

Approximately how many milliliters of water are needed to prepare 250 mL of a 70% ethanol solution using 100% ethanol?Record your answer as a numerical value only with no decimal places.

QUESTION 9

A pharmacist has on hand a 8% (w/w) ointment and a 16% (w/w) ointment. In what ratio should the two ointments be mixed in order to prepare a 10% ointment. Enter your answer as a ratio (X:Y) of 8% :16% ointments.

Solution

let the volume f water required be = V ml

volume of the solution = 250 ml

70% of the solution is ethanol = 70/100 * 250 = 175 ml

therefore the volume of water in the solution is = 250 -175 = 75 ml

9 .

let the weight of the ointment be = 100 units

let the weight of 8% ointment be = x units

let the weight of 16% ointment be = y units

part of 8% ointment = .08x

part of 16% ointment = .16y

the final mixture is = 10% of 100 = 10

x+y=100 -------->(1)

.08x + .16y = 10 ------->(2)

solving (1) and (2)

we get x = 75 and y = 25

hence the ratio is X : Y = 75 : 25 = 3 : 1