How would I solve these atoms/mass/mole problems?Find the # of atoms of phosphorus (P) in 3.44 moles of phosphorus. What is the mass of 0.38 moles...

There are two basic relationships that you need to learn
and remember and then mole/mass/atoms problems will be easy to
do.

First, one mole of any substance, whether it is an
element or a compound contains Avogardro's number of atoms or molecules of that
substance.  Avogadro's number being 6.023 x 10^23.

Thus, in
one mole of hydrogen there are 6.023 x 10^23 atoms of hydrogen.  In one mole of HCl
there are 6.023 x 10^23 molecules of HCl.  To find the number of atoms in a given number
of moles, just multiply the number of moles by Avogardro's number.  Let's do an example
using Potassium (K) and assume you have 2.6 moles of potassium.  2.6 x 6.023 x 10^23 =
1.566 x 10^24 atoms of potassium.

If instead you are given
the number of atoms of the substance, just divide the number of atoms given by
Avogadro's number to get the number of moles.  Let's do an example and assume we have 14
x 10^25 atoms of Calcium.  How many moles do we have?

14 x
10^25 atoms divided by 6.023 x 10^23 atoms /mole = 2.324 x 10^2 moles of
calcium.

Second, one mole of any element is equal in mass
to the atomic mass of that element.  Thus, one mole of iron has a molar mass of
55.847g/mole.  To find the actual mass of the substance, you multiply the molar mass by
the number of moles.  Using iron as the example, if you had 0.2 moles of iron you would
have 0.2 moles x 55.847 g/mole = 11.169 g of iron.

Using
these two relationships you can solve everyone of these mole/mass/atom
problems.