More physics homework?

Question

4. estimate the number of water molecules in a cup (8 oz. exactly) of water 1(fluid) = 0.0296 L. [hint. you may find it helpful to recall that the mass of a hydrogen atom is about 1.67x10(to the power of -27)kg and that an oxygen atoms mass is about sixteen times that value.

Answer 1

You'll need to do the math yourself since I don't have a calculator handy, but here's what you should do:

The steps are first to find out the mass of 8 oz. of water (0.0296 L).

Then find out the mass of one water molecule, using the information given.

To estimate the number of molecules in the cup of water you would simply divide the mass of the cup of water by the mass of one water molecule.

For the first part you can remember that water has a density of 1 g/ml, or 1 kg/L.

You have 0.0296L, so you can multiply 1Kg/L to get 0.0296 Kg.

For the 2nd part, you should remember that one water molecule has two hydrogen atoms, and one oxygen atom in it.

From the weight information you were given the mass of one water molecule would then be given by:

mass of one water molecule = 2*(1.67x10^-27kg) + (1)*(16)*(1.67x10^-27kg)

Once you do the math for that, you can divide the two results to get the number.

Hope this helps.