What Causes the Increase in Density of a Hard Boiled Egg?

[ciubba]

I have determined in lab that a hard boiled egg is denser than a raw egg; however, I am not sure that I entirely understand this phenomenon. Assuming my data is correct, my assumptions are as follows:

1. Boiling the egg weakened its exterior, allowing water to enter the shell, thus increasing its mass.
2. The denaturing of the proteins altered the properties of the egg in such a manner that the density of the egg was increased.​

Have I stumbled upon the proper line of inquiry?

 

[phinds]

I don't have any scientific idea in answer to your question, but neither sounds right. Certainly changing the form of the proteins doesn't seem likely to change the mass of the egg.

Are you sure about your measurement?

The one thing I can think of is that I don't think raw eggs have an air cavity, but boiled eggs do. Perhaps the mass of the raw egg material is the same but what's inside the shell now includes some air. Doesn't seem like that would make a measurable difference but I suppose that depends on how sensitive your scale is.

Ah ... another thought. Maybe the size of the whole shell is reduced a bit by the boiling, along with the innards being made to occupy a smaller volume and the air doesn't fully make up the different (to keep the shell from shrinking). Have you measured the volume to be the same and the weight to be more or the weight to be the same and the volume to be less?

What exactly DID you measure to conclude that the boiled egg is more dense?

 

[ciubba]

I don't have any scientific idea in answer to your question, but neither sounds right. Certainly changing the form of the proteins doesn't seem likely to change the mass of the egg.

Are you sure about your measurement?

The one thing I can think of is that I don't think raw eggs have an air cavity, but boiled eggs do. Perhaps the mass of the raw egg material is the same but what's inside the shell now includes some air. Doesn't seem like that would make a measurable difference but I suppose that depends on how sensitive your scale is.

Ah ... another thought. Maybe the size of the whole shell is reduced a bit by the boiling, along with the innards being made to occupy a smaller volume and the air doesn't fully make up the different (to keep the shell from shrinking). Have you measured the volume to be the same and the weight to be more or the weight to be the same and the volume to be less?

What exactly DID you measure to conclude that the boiled egg is more dense?

We weren't allowed to mass the eggs directly, so I added salt to a water solution until the egg appeared to equal its density i.e. it "just floated". At this point, I used a 10 mL glass pipet to mass 10 mL of the solution, which I subtracted from the mass of the glass pipet to obtain the mass of the salt water,. Knowing that the volume of the water was 10 mL, I was able to determine the density.

I'm somewhat confident that my results are correct as I recreated the experiment in my kitchen a few moments ago by placing both a raw egg and a hard boiled egg in the same salt solution. Evidently, the boiled egg sank whilst the raw egg floated. Unfortunately, we have not covered any chemical mechanisms in class that would explain the change in density of the egg.

 

[Borek]

I don't think raw eggs have an air cavity

They do. Whether the size of the cavity is the same in the raw and boiled egg is another thing.

 

[phinds]

They do. Whether the size of the cavity is the same in the raw and boiled egg is another thing.

Borek, you know the most amazing things. :w

 

[ciubba]

They do. Whether the size of the cavity is the same in the raw and boiled egg is another thing.

So, if the air cavity was penetrated by the solid mass of denatured proteins, what effect would that have on the volume and mass of the egg as a whole? It seems to me that unless the air can escape from the egg density should remain constant. If it can escape from the egg then my results should be opposite.

 

[Borek]

It seems to me that unless the air can escape from the egg

Have you ever seen boiling egg? It bubbles. That means it also sucks the air inside while cooling. It can also mean it sucks water if you put it in the cold water after boiling (like I do, to make it easier to remove the shell).

 

[ciubba]

Have you ever seen boiling egg? It bubbles. That means it also sucks the air inside while cooling. It can also mean it sucks water if you put it in the cold water after boiling (like I do, to make it easier to remove the shell).

No, I prefer my eggs soft-boiled! Thank you, I understand what produced the change in density now.