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Part 1: Mass Percent<br />
Mass percent (also called percent by mass, weight percent, or percent by weight) compares the<br />
mass of the solute to the entire mass of the solution.<br />
Notes:<br />
Mass percentage is one way of representing the concentration of an element in a compound or a component in a mixture.<br />
Mass percentage is calculated as the mass of a component divided by the total mass of the mixture, multiplied by 100%.<br />
Part 2: Parts per Million<br />
Parts per million (ppm) is another measure of concentration. It is similar to mass percent. But<br />
mass percent indicates the number of grams of solute per 100 g solution. Parts per million<br />
indicates the number of grams of solute per 1,000,000 g solution. This measure of concentration is<br />
often used to express the concentrations of very dilute solutions.<br />
Notes:<br />
This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred,<br />
so parts per million or ppm means out of a million.<br />
Part 3: Molality<br />
Molality (m) is the ratio of the moles of solute to the kilograms of solvent. Note: this is the first<br />
measure of concentration that is concerned with the mass of the solvent, not the mass of the<br />
solution as a whole.<br />
Notes:<br />
The molal unit is not used nearly as frequently as the molar unit. A molality is the number of moles of solute<br />
dissolved in one kilogram of solvent.<br />
Part 4: Grams per Liter<br />
To express the concentration of a solution in grams per liter, you must know the mass of the solute<br />
and the volume of the solution, not just the volume of the solvent.<br />
Notes:<br />
A gram per litre or gram per liter (g/L or g/l) is a unit of measurement of mass concentration that shows how many<br />
grams of a certain substance are present in one litre of a usually liquid or gaseous mixture.<br />
Suppose you wanted to know what the concentration would be before making the solution. Could that<br />
be done? In order to relate the volume or mass of solvent to the volume of solution, you would have<br />
to know the density of the solution. You will see how solution density can be used to calculate<br />
molarity in the next section.<br />
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