How to Calculate the Volume of a Powder Mixture

By James Rutter
The particles in powder mixtures trap air, affecting the powder's volume.

You can easily measure the packing, or bulk, volume of a given amount of a powder mixture by placing it in a graduated cylinder. But any powder mixture will contain some air, and the packing volume, no matter how tightly pressed in the graduated cylinder, will not represent the true volume of the material itself. To find the volume and density of the actual powder mixture you will need a liquid that will not dissolve or chemically alter any of the powders in the powder mixture. For instance, water will dissolve a mixture of sugar and salt.

Place a filter on the scale and note the weight. Measure out 5 g of the powder mixture by placing it on a scale until the scale reads 5 g over the weight of the filter. Set the powder mixture on the filter aside.

Place a graduated cylinder on the scale and note the weight. Add 25 milliliters (ml) of liquid to the graduated cylinder. Determine the weight of the liquid by itself by subtracting the weight of the graduated cylinder from the weight reading on the scale.

Determine the density of the liquid by dividing the mass of the liquid by the 25 ml volume. Write this density number down and label it DL.

Add the 5 g of powder to the pycnometer and weigh the pycnometer, stopper and powder on the scale. A pycnometer contains a stopper and a small capillary tube that sucks out any excess air in a mixture. Write down this weight and label it M1.

Add liquid from the graduated cylinder to the pycnometer until it is full. Place the stopper in the pycnometer. Wipe away any expelled liquid with a filter until the pycnometer stops expelling air and liquid.

Weigh the powder, pycnometer and liquid mixture on the scale. Label this weight M2. Determine the mass of the liquid (ML) used to fill the pycnometer by subtracting M1 from M2.

Determine the volume of the liquid (VL) added to the pycnometer by using the equation Volume = weight/density, or in this case, VL = ML/DL.

Determine the volume of 5 g of powder by subtracting VL from 25 ml, which is the total volume of space inside the pycnometer.

Tip

You can determine the particle density of the powder mixture by using the equation density = (mass/volume).

About the Author

Since 2005, James Rutter has worked as a freelance journalist for print and Internet publications, including the “News of Delaware County,” “Main Line Times” and Broad Street Review. As a former chemist, college professor and competitive weightlifter, he writes about science, education and exercise. Rutter earned a B.A. in philosophy and biology from Albright College and studied philosophy and cognitive science at Temple University.