Percentage, ratio strength and Other Expressions of Concentrations

What is Concentration?

Amount / Volume

What is Molarity (M)?

moles (gram MW) / Liter of solution

What is Normality (N)?

equivalents (gram Eq. W) / Liter of solution

What is Molality (M)?

moles (gram MW) / 1 kg solvent

What is Percentage (% w/v)?

No. of g of solute in 100 mL of solution

What is Percentage (% v/v)?

No. of mL of solute in 100 mL of solution

What is Percentage (% w/w)?

No. of g of solute in 100 g of mixture

What is g/g?

grams of solute per gram of solution

What is ppm?

1 gram of solute per 1,000,000 milliliters of solution

What is ppb?

1 gram of solute per 1,000,000,000 milliliters of solution

What is Ratio strength?

A ratio of the amount of solute to the total amount of solution

What is the molarity of a solution prepared by dissolving 3.5 g of potassium chloride in water to make 175 mL of solution? (m.w. of KCl = 74.55)

0.268

A hospital pharmacist is preparing an intravenous calcium gluconate solution by dissolving 6.0 g of calcium gluconate in 250 mL of sterile water. Calculate the molarity (M) of the calcium gluconate solution. (Molecular weight of calcium gluconate = 430.4 g/mol)

0.0556

How many milliliters of liquefied phenol should be used in compounding the prescription? Liquefied phenol 2.5% (v/v) Calamine Lotion ad 240 mL. Sig. For external use.

6

How many grams of potassium permanganate should be used in compounding the following Rx?

Rx Potassium permanganate 0.02%

Purified Water 250 mL

0.05

A cyclosporine ophthalmic emulsion Restasis contains 0.05% w/v cyclosporine in 0.4 mL vials. Calculate the content of cyclosporine, in mg per vial

0.2

Peppermint spirit contains 10% of peppermint oil. What volume of the spirit will contain 75 mL of peppermint oil?

750

How many grams of Benzocaine should be used in compounding the following Rx?

Rx: Benzocaine 2%

Polyethylene Glycol Base ad 2 g

Make 24 such suppositories

Sig. Insert 1 as directed

0.96 g for 1 suppository

What is mg%?

mg of solute per 100 mL of solution.

What is the PPM of 5 mg of solute in 1 liter of water?

5

Express this concentration as percentage strength (w/v).

2,500 PPM

0.25

If a commercially available insulin preparation contains 1 ppm of proinsulin, How many micrograms of proinsulin would be contained in a 10-mL vial of insulin?

10

A commercially available growth hormone preparation contains 5 ppb of a protein impurity. How many nanograms of this impurity would be present in a 20-mL vial of the growth hormone solution?

100

How do you do Concentration conversion of ratio strength to % strength?

Convert ratio strength to % strength by changing the last 2 zeros to % sign and converting the remaining ratio.

1:100=

1%.

1:200=

0.5%.

3:500=

0.6%.

1:2500=

0.04%.

1:10,000=

0.01%.

An injection contains 0.50% w/v of Lidocaine HCl.Express the concentration as a ratio strength.

1:200

What is the ratio strength (w/v) of a solution made by dissolving five tablets, each containing 2.25 g of sodium chloride, in enough water to make 1800 mL?

1:160

If a liquid vitamin preparation contains 0.16 μg ofvitamin B12 per 5 mL, what is the ratio strength ofthe preparation?

1:31,250,000

Convert 2.5% w/v to mg/mL

25/1

Convert 1:5,000 (w/v) to mg/mL

0.2/1

Convert 4 g/L (IV infusion) to mg/mL

4/1

mg% =

mg solute/100 ml solution

𝑚𝑔/𝑑𝐿

mg of solute/100 mL of solution

A pharmaceutical solution contains 150 mg of an active ingredient dissolved in 75 mL of solvent. Calculate the mass percent (mg%) of the active ingredient in the solution

200%

What is Parts Per Million (PPM) Equivalent to?

1 mg/L, 1 g/1000 L, 0.0001% w/v

A solution contains 5 mg of solute in 1 liter of water. What is the PPM?

5 / 1,000,000

A paracetamol solution is prepared at a concentration of 2,500 PPM. Express this concentration as percentage strength (w/v).

0.25%

An ophthalmic solution is preserved with 0.0008% (w/v) of an antibacterial. Express this concentration as a ratio strength.

1:125000

Tretinoin gel (RETIN-A MICRO) is available in a 0.04% w/w concentration. Which of the
following represents an equivalent strength?

6 mg tretinoin /15 g gel

In acute hypersensitivity reactions, 0.5 mL of a 1:1000 (w/v) solution of epinephrine
maybe administered subcutaneously or intramuscularly. Calculate the milligrams of
epinephrine given. 

0.5

An eye drop has the following formula:
Fluorometholone 0.1% w/v
Neomycin sulfate 0.35% w/v
Benzalkonium chloride 0.004% w/v
Isotonic vehicle ad 5 mL
Calculate the ratio strength of benzalkonium chloride in the formula.

1:25000

Purified water contains not more than 10 ppm of total solids. Express this concentration
as a percentage.

0.001%

An injection contains 0.50% (w/v) of lidocaine hydrochloride and 1:200,000 (w/v) of
epinephrine. Express the concentration of lidocaine hydrochloride as a ratio strength
and that of epinephrine as a percentage. 

1:200

0.0005%

1 pt =

473 mL

Potassium Permanganate Tablets 0.2 g
Disp # 100
Sig: two tablets in 4 pt of water and use as directed.
Express the concentration, as a ratio strength, of the solution prepared according to the directions given in the prescription.

1:4730

How many grams of sodium fluoride should be added to 100,000 liters of drinking water containing 0.6 ppm of sodium fluoride to provide a recommended concentration of 1.75 ppm?

115