Answer 1:
This is a fun question! Objects float in materials
that are more dense than the object itself.
Density is a measure of how much substance there
is per unit volume of material. So that means more
dense objects have a higher amount of "stuff" in a
given volume, and the opposite is true for
materials that are less dense.
In order to make the egg float, we need to make
it less dense than the water surrounding it. As
your teacher has probably explained in class,
adding salt makes the surrounding solution more
dense. How much salt we need to add will vary from
egg to egg, since the density of each egg will
probably be slightly different. However, we can
make a rough estimation! According to a couple of
websites I found online, eggs have a density of
about 1.03g/mL. That means in a volume of 1mL,
there is about 1.03g of the stuff that comprises
an egg. The density of pure water is about
1.00g/mL. So let's calculate how much salt we need
to add to account for this difference in
densities!
The first thing we need to keep in mind is the
formula for density. Density is equal to mass
divided by volume, or:
ρ = density = (mass in grams)/(volume in
mL)
To make the calculation a little easier, let us
assume we have 1L of water. We need to figure out
how many grams of salt to add to the water to
increase the density by at least 0.03g/mL. The
equation we want to solve for this problem is:
0.03g/mL = (density of saltwater)  (density
of water)
We can read this equation as: "0.03 is
equal to the difference in the density of pure
water and the density of water with salt added to
it"
Now, use the equation for density:
0.03g/mL = (1000grams water + Xgrams
salt)/(1000mL of water)  (1000grams
water)/(1000mL of water)
Let's rearrange for the variable we are trying
to solve for:
0.03 + 1000g/(1000mL water) = (1000grams
water + Xgrams salt)/(1000mL of water)
Xgrams salt = (1000mL water)*(0.03g/mL +
1000gWater/1000mLWater)  1000g water
X = 30g salt ~ 2 tablespoons
Now, it is important to keep in mind that the
density of the egg varies and you may not use 1L
of water, but some other amount. This means the
amount of salt we would need to add will vary as
well, but this is a ballpark estimate of about
how much salt we should add (i.e. we would be
adding tablespoons as opposed to cups of salt to
1L of water). I hope this helps!
