Knowledge database: Stoichiometry: Ratios

Knowing the basics related to the use of ratios can be very useful in chemistry, especially when working with various different units of measurement.

A ratio is defined as the relative size of two quantities expressed as the quotient of one divided by the other. According to this definition, a ratio of a to b is often written as a/b or a:b. However, in the context of chemistry it is more practical to define the ratios that are most commonly used in stoichiometry.

All of them can be expressed by a single formula which can be seen on the image above. Here we will mention the three most common variations:

1) The mass ratio: ζ(A,B) = m(A) / m(B)

2) The volume ratio: ψ(A,B) = V(A) / V(B)

3) The molar ratio: r(A,B) = n(A) / n(B)