Title: Concentrations by mass/volume and %
Course: BTEC-1100-301-302-303-F21 > Section: Module 1 - Calculations and Measurements

Making solutions at a particular concentration is a fundamental part of laboratory work in biotechnology. You, as a biotech technician, need to know how to calculate concentration based on molarity and percentage to correctly make solutions.

Concentration
an amount of some substance per a set volume.
(Concentration = Amount/Volume)

One way of describing concentration is in units of mass/volume, for example 20 mg/mL, 50 g/L, or 750 mg/L. This simply describes the amount of solute within the total solution volume.

Another way of describing concentration is with percentage. Percent, by definition, means ‘per 100’. Because we work mostly with liquid solutions, the units for the denominator (bottom) are nearly always mL. The units for the numerator (top) are either g or mL, depending on whether the solute is a solid or liquid.

5% (w/v) = 5 g solute/100 mL solution
5% (v/v) = 5 mL solute/100 mL solution

Note that the w and v refer to weight (in grams) or volume (in mL). If w/v or v/v is not stated, assume w if the solute is a solid, and v if the solute is a liquid. (This is because the easiest way to measure solids is with weight; the easiest way to measure liquids is with volume.)