Video Transcript
A saline solution was prepared by dissolving nine grams of NaCl in water to produce a solution with a total volume of 1000 milliliters. What is the mass-by-volume percentage concentration, percent mass by volume, of the saline solution?
This solution was prepared by dissolving nine grams of sodium chloride in water so that once combined, the solution would have a total volume of 1000 milliliters. Using this information, we want to calculate the mass-by-volume percentage concentration. Even if we don’t know the equation for mass-by-volume percentage concentration, this sentence gives us a clue. We will need to divide a mass by a volume. And as we are calculating a percentage, we will also need to multiply by 100 percent.
Let’s consider the generic equation for finding a percentage. Percentage equals the part divided by the whole times 100 percent. We can combine the generic equation with our equation for mass-by-volume percentage concentration to make it more specific. We need to take the mass of the part and divide it by the volume of the whole, or the total volume.
In our example, the sodium chloride is the solute, the substance that dissolves. It is one component of the solution, which is the total mixture. The sodium chloride represents the part, and the solution represents the whole. We can substitute the nine grams and 1000 milliliters into our equation. Notice that the numerator has a mass unit and the denominator has a volume unit.
Typically when calculating the mass-by-volume percentage concentration, the mass should have a unit of grams and the volume should have a unit of milliliters. We perform the calculation and determine that the percentage concentration of the saline solution is 0.9 percent mass by volume.
