Pharmaceutical Calculation I

A pharmacist diluted 200mL of 20% (w/v) aqueous solution to 1 liter. What will be the percentage strength of the resultant solution?

Answer explanation

(20%)(200mL) = x(1000mL) x = 4%

How many milliliters of a 1:2000 (w/v) solution of a sodium chloride can be made from 120 mL of a 0.5% solution ?

Answer explanation

1 : 2000 = 0.05% (120mL)(0.5%) = V₂ (0.05%) V₂ = 1200mL

A 1:4 mixture containing codeine sulfate, with lactose as an inert diluent, is prepared. How many milligrams of lactose are present in 1.25g of the mixture ?

How many milligrams of mercury bichloride are needed to make 200mL of a 1:500 w/v solution?

What is the ratio strength of a 1/4% (w/v) solution ?

If 150mg of strychnine sulfate are intimately mixed with 7.35g of lactose, an inert substance, what is the ratio strength of strychnine sulfate in the mixture?

A viral vaccine is preserved with 1 : 10,000 solution of benzalkonium chloride ( a solid). How would we express this concentration as percentage ?

How many grams of lactose should be added to 120mg of strychnine sulfate to make a 1 : 20 trituration ?

Answer explanation

120 x 19

=2280mg

=2.28g

How many milligrams of a 1 : 25 trituration of atropine should be used to prepare 40 capsules, each containing 0.4 mg of atropine ?

Answer explanation

25 x 16 = 400 mg

How many millimeters of a 10% w/v Merthiolate solution should be diluted with water to make 440 mL of a 0.25% w/v Merthiolate solution?

Answer explanation

Let x = the milliliters of 10% Merthiolate solution:

g merth (10%) = g merth (0.25%)

(0.10g/mL)x = (440mL)(0.0025g/mL)

= 1.1g

x= 11mL