From the following formula of hydrophilic ointment solve for the quantities of each ingredient needed to prepare 5 lb (Avoir) of the ointment. Note: 1 lb = 454 g (avoir)

Question

Methylparaben 0.25 g

Propylparaben 0.15 g

Sodium lauryl sulfate 10 g

Propylene glycol 120 g

Stearyl alcohol 250 g

White Petrolatum 250 g

Purified Water, add 1000 g

a) Use Ratio & Proportion for methylparaben and propylparaben.

b) Use Dimensional Analysis for sodium lauryl sulfate and propylene glycol.

c) Use Factor method for stearyl alcohol and white petrolatum.

d) Solve for the quantity of water needed in the Master and working formula.

Answer 1

Methylparaben 0.25 g

Propylparaben 0.15 g

Sodium lauryl sulfate 10 g

Propylene glycol 120 g

Stearyl alcohol 250 g

White Petrolatum 250 g

Purified Water, add 1000 g

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Total mass = 1630.4 g

1630.4 g x 1 lb / 454 g = 3.59 lbs

a) methylparaben: 0.25 g / 3.59 lbs = x g / 5.00 lbs and x = 0.35 g

propylparaben: 0.15 g / 3.59 lbs = x g / 5.00 lbs and x = 0.21 g

b) 10 g SLS / 3.59 lbs x 5 lbs = 14 g

120 g propylene glycol / 3.59 lbs x 5 lbs = 167 g

c) 250 g stearyl alcohol / 3.59 lbs x 5 lbs = 348 g

250 g petroleium / 3.59 lbs x 5 lbs = 348 g

To me, the Factor method is the same as dimensional analysis, so I'm not sure what they want.

d) I have no idea what the Master and working formula are, but here is the calculation for water...

1000 g water / 3.59 lbs x 5 lbs = 1390 g