Science Buddies: "Ask an Expert"

How do I find the density of an egg? I know that density is mass divded by volume but how do you find the volume of an egg? My science teacher told me that I can do this by water displacement but, what would I write after that? How would I do this using a measuring cup?
Help me please. I feel like I'm in the thrid grade again.
-Elle

Hi Elle,
What your teacher was referring to is that you can fill your measuring cup up to a certain known amount of water, say 50 mL. Once you put the egg in, if the water rises to 60 mL, you can say that 60 mL - 50 mL (or final volume - initial volume) = 10 mL, or the volume of the egg. You can then plug it into the equation with mass. Hope this helps, good luck!

Thank you so much.

The egg has to "sink" in the liquid by itself or you will have to use something to hold it completly under water and account for the volume taken up by whatever you use to hold the egg down.

Hello. I working on this same experiment with floating an egg in salt water, however when I measure the density of the egg, I come up with 57 grams(mass of egg)/ 75ml of volume for egg(100ml of water then 175ml after egg was added). Therefore, the density I come up with is .76g per cm3. Now if water is 1g per cm3, then the egg should float without salt since 1g per cm3 is denser than .76g per cm3? What am I missing here?

wbhdjhhmh wrote:What am I missing here?

Good question. Obviously there is something wrong. What does your scale say about the weight of the 100ml and 175ml of (salt?) water? You need a cross check on the accuracy of your scales to see if the problem is in the weight. Did the egg float or did you have to hold it down to measure its volume?

Actually, I didn't use a scale to measure the tap water. Just from information gathered from Google and Wikipedia on what an egg's mass is and then placed it in the water where it floated to the bottom which gave me the 75ml volume of the egg. I got the 1g per cm3 for the density of water from the internet as well. Do I need to buy a scale to figure out these measurements?

If you didn't measure the weight or mass of the egg with any type of reasonably accurate instrument, then that is exactly what you missed.

Online resources can only give you approximations or ball park expected values for things. If you accurately weigh any given egg, you can't expect it to precisely match the expected value. There are significant variations in eggs. Stores sell eggs based on size and quantity not weight. Can you expect a dozen small eggs to weigh the same as a dozen extra large eggs? The majority of the mass or weight of a freshly layed egg is water. The membrane and shell is permeable meaning air and moisture can pass through it at some small rate. Depending on the humidity and temperature of the surroundings, moisture loss or gain (including the mass of the water) will occur so if your scale is accurate enough to detect minute differences, the mass (weight) can change over time.