Science Buddies: "Ask an Expert"

I am doing the project Mixing Your Own Marshmallows: Finding the Right Ratio of Sugar to Corn Syrup. I would like to extend the project by measuring the density of the marshmallows from each recipe, but I do not know how to do it. Please tell me how I use the scale, graduated cylinder and Archimedes' principle to do this. It is all that is given to me under Variations on the Website.

Hi,

Density is mass over volume. So a simple way to calculate density is to make some marshmallows and take out certain amounts of them. Then measure these samples with a balance and record their mass preferably in grams. Afterwards, fill up a container with a known amount of water near the top so that it doesn't overflow yet. Place another container underneath this container. Then gently place one of your marshmallow samples into the water. Measure the water that spilled out after the marshmallow sample was put into the container in a graduated cylinder. Record the volumes of the water displaced. Archimedes' principle of buoyancy says that the volume of an object is equal to the volume of the water displaced by the object itself. You found the volume of the marshmallow, so take the mass you measured and divide it by the volume you just found. Voila, you calculated density! Try doing multiple trials to get accurate results. An easier way to do this is to roll up the marshmallow sample and place it into a graduated cylinder with a known level of water. Make sure the sample doesn't get stuck! Measure the new water volume and subtract the new water volume from the water volume you started with. The difference is the volume of the marshmallow. Hope that helps!

One caution - the marshmallow may absorb water. If you measure quickly this might not matter.

To see if it does matter, try measuring volume with the marshmallow wrapped in a single layer of plastic-wrap, then try it again with the same marshmallow without the wrap. If you get about the same result, water soaking into the marshmallow doesn't matter. If they're different, you'll want to protect them from the water.

You will need to weigh and dunk into water every marshmallow you create, as they are likely to be different sizes. But if you calculate density it doesn't matter if the individual marshmallows are different sizes - if they're all made about the same their density should be pretty consistent.

Thank you so much. Your input is appreciated and helps clarify the procedure for us.