### Video Transcript

What is the equation that gives
percentage purity in terms of the mass of the pure chemical and the mass of the
sample?

To help us understand this
question, let’s consider two beakers. The beaker on the left only
contains water, so this sample is a pure substance. The beaker on the right however
contains sodium chloride and water, a mixture of two different substances. So the sample is impure. We can quantify how pure a
substance is with purity, a measure of the extent to which a substance is free from
impurities.

To answer the question, we need to
determine an equation that gives the percentage purity. As we are told that purity is a
percentage, let’s consider how a standard percentage is calculated. To find a percentage, we divide the
part in question by the whole then multiply by 100 percent. So, for example, if we wanted to
know what percentage of the dots is pink, we would divide three, the number of pink
dots, by 10, the total number of dots, then multiply by 100 percent.

When determining purity, we want to
know what percentage of a sample is pure. This means that the part must be
the amount of pure chemical and the whole must be the amount of sample.

Using what we know about
percentages and the terms mass of the pure chemical and mass of the sample, we can
construct an equation for percentage purity. Percentage purity equals the mass
of the pure chemical divided by the mass of the sample times 100 percent. Using this equation, we can see
that a pure sample has a percentage purity of 100 percent, while an impure sample
has a percentage purity of less than 100 percent.

In conclusion, the equation that
gives percentage purity is percentage purity equals mass of pure chemical divided by
mass of sample times 100 percent.