Video Transcript
A 30-gram tube of antiseptic cream contains one percent weight by weight of cetrimide. What mass of cetrimide does the cream contain?
Percent weight by weight is a common pharmaceutical notation. It has the same meaning and equation as percent mass by mass. Recall that percent mass by mass, and therefore percent weight by weight, can be calculated by dividing the mass of the solute by the mass of the solution and multiplying by 100 percent.
In this example, the cetrimide is a component of the antiseptic cream. The cetrimide is the solute, and the antiseptic cream is the solution. We know the mass of the antiseptic cream, and we know that the solution is one percent weight by weight of cetrimide. We want to determine the mass of cetrimide in the cream. We can substitute the percent weight by weight and the mass of the solution into the equation.
As we do not know the mass of the solute, we can call this variable 𝑚. To solve, we begin by dividing both sides of the equation by 100 percent. Then, we multiply both sides of the equation by 30 grams. This gives us a mass of cetrimide of 0.3 grams.
