Question

What is the final percentage strength (w/w) of a product made by combining 30 grams of a 50% powder with 20 grams of a 10% powder and 50 grams of lactose (a diluent with 0% active ingredient)? Enter your answer as a number with the appropriate units.

QUESTION 2

When using the method of alligation, active ingredient should be set to a strength of _____%.

QUESTION 3

How many milliliters of a 1% (w/v) stock solution of a drug should be used to prepare 4000 mL of a 1:10,000 topical solution?Record your answer with no decimal places and with the appropriate units.

Answer 1

1.

We combine 30g of 50% powder with 20g of 10% powder and 50g of 0% lactose

So we can write

Summation (product of strength of powder * mass of powder) = (Final Strength * final mass)

0.5 * 30 + 0.10 * 20 + 0 * 50 = S * ( 30 + 20 + 50)

17 = S * 100

S = 17 / 100 = 0.17

So percentage strength = 0.17 * 100% = 17 %

2.

When using alligation active ingredients should have a strength of 100% and the strength of dilutents will be 0%

3.

C1 = 1/10,000 = 0.0001 = 0.0001 * 100% = 0.01% w/v

C2 = 1% w/v

V1 = 4000 mL

V1 * C1 = V2 * C2

V2 = V1 * C1 / C2

V2 = 4000 mL * 0.01% / 1%

V2 = 40 mL

So ,

40 milliliters of a 1% (w/v) stock solution of a drug should be used to prepare 4000 mL of a 1:10,000 topical solution