% mass by vol
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% mass by volume concentration (or % wt vol) is quite useful as a laboratory description for preparing solutions. It is used in laboratories where solutions of the same concentration are prepared repeatedly. A 1.5 % NaCl solution is prepared my massing 1.5 grams of salt and adding it to water in a 100 mL volumetric flask. The solution is then diluted to the line on the flask in the same manner that a molarity solution is prepared. The % mass by volume is defined as 100 times (grams solute/mL of solution). It can also be thought of as (grams of solute/100 mL of solution).

The laboratory worker does not need to use the molar mass to prepare the solution each time, and errors are less frequent. For these reasons % mass by volume is frequently used in medical laboratories.

In fact, a solution of exactly 1.0 M NaCl (58.4425 g NaCl = 1 mole) may be prepared by expressing the concentration as 5.84 % mass by vol. The technician may prepare the solutions from the percent, but other workers may use the molarity.

As with a molarity solution, a given volume of solution delivers a fixed number of moles of solute. Measuring the volume of the solution also measures the amount of solute in grams or moles.

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