Concentration Calculations (w/w, w/v, v/v)


  **A percentage expresses the number of parts of a particular substance per 100 parts


Solute- Is a substance (solid) that is dissolved in a liquid to form a solution

Solvent- Is a substance (liquid) in which the solute is dissolve

Solution- A mixture consisting solute and solvent

Concentration- Is the measure of how much of a given substance there is mixed with another substance
Ex) sugar and water- sugar is the solute and water is the solvent

Weight per Weight (W/W): Concentration of a solid dissolved in another solid

Ex) Betamethasone 0.1% cream, 120g tube is dispensed to a patient. How much Betamethasone is in the 120g tube?

 If       0.1 g = 100 g (parts)

Then       X   = 120 g            ---0.1 X 120g / 100 g = 0.12g of Betamethasone is in a 120g tube

Weight per Volume (W/V): Concentration of a solid dissolved in a liquid < 5g w/v means there is 5g in a 100 ml solution >

Ex) A prescription calls for 120 ml of a 2% gentamicin solution. How much gentamicin powder is needed?

If           2 g = 100 ml

Then         X  = 120 ml       ---- 2g X 120 ml / 100 ml = 2.4g gentimicin powder is needed

Volume per Volume (V/V): Concentration of a liquid dissolved in another liquid < 15% v/v means there is 15 ml in every 100 ml solution >

Ex) An alcohol solution is labeled as 10% v/v. How much alcohol is in 200 ml?

If           10 ml = 100 ml

Then         X    = 200 ml      -------------- 10 ml X 200 ml / 100 ml = 20 ml of alcohol is in 200 ml