Question Video: Identifying the Equation Used to Calculate the Percentage by Mass of a Solution Chemistry

Which of the following equations can be used to calculate the percentage by mass, percent mass by mass, of a solution? [A] % (m/m) = (mass of solute/mass of solvent) × 100% [B] % (m/m) = (mass of solute/mass of solution) × 100% [C] % (m/m) = (mass of solute × mass of solvent) × 100% [D] % (m/m) = ((mass of solute × mass of solution)/100%) [E] % (m/m) = ((mass of solute + mass of solvent)/mass of solution) × 100%

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Video Transcript

Which of the following equations can be used to calculate the percentage by mass, percent mass by mass, of a solution? (A) Percent mass by mass equals mass of solute divided by mass of solvent times 100 percent. (B) Percent mass by mass equals mass of solute divided by mass of solution times 100 percent. (C) Percent mass by mass equals mass of solute times mass of solvent times 100 percent. (D) Percent mass by mass equals mass of solute times mass of solution divided by 100 percent. (E) Percent mass by mass equals mass of solute plus mass of solvent divided by mass of solution times 100 percent.

The symbol for percentage by mass, m slash m, gives us a clue as to what we should look for in the equation. The correct equation should have a mass unit divided by another mass unit. As such, we can eliminate answer choices (C) and (D) as neither equation has a mass unit in the denominator. Next, let’s consider the generic equation for finding a percentage. Percentage equals the part in question divided by the whole times 100 percent. How does this apply to a solution? A solute, the minor component, is combined with a solvent, the major component, to produce a solution. The solution is the total mixture of the solute and solvent and can take the place of the whole in the percentage equation. This means that we can eliminate answer choice (A) as the mass of the solution, not the solvent, should be in the denominator.

Now, let’s take a look at answer choice (E). In the numerator, we are adding together the mass of the solute and the mass of the solvent. Since the solute and the solvent make up the solution, adding their masses together will give you the mass of the solution. This means that in answer choice (E), we are taking the whole and dividing it by the whole. This will always give you a value of 100 percent. This leaves us with answer choice (B) mass of solute divided by mass of solution times 100 percent. The solute is one of the components that makes up a solution. It is the part and the solution is the whole.

“Which of the following equations can be used to calculate the percentage by mass of a solution?” (B) Percent mass by mass equals mass of solute divided by mass of solution times 100 percent.

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