[rosario2468]

The recommended daily allowance (rda) of iron in your diet in 15mg. How many moles is this? How many atoms?
here are the answers to choose from....

• 2.5 X 10^-4 mol; 1.5 X 10^20 atoms
• 2.7 X 10^-4mol;1.5 X 10^20 atoms
• 2.7 X10 ^-4 mol; 1.6 X10^20atoms
• 2.5 X10 ^-4 mol; 1.6 x 10^20 atoms

[il juche]

Hey, this one's the answer I believe.

2.7 X10 ^-4 mol; 1.6 X10^20 atoms

Do you want a full calculated explanation?

[il juche]

Ok, so first calculate the molecular weight. This part is easy. It's just:

molecular weight = 55.845 amu (you get this by looking at the atomic weight on the periodic table) which can also be written as 55.845 g/mol (this is called the molar mass)

Now, we use the formula:

amount of substance in grams
------------------------------------------ = amount of substance (in moles)
molecular weight

So:    .015 g Fe
       -------------------- = ~ 2.7 x 10^-4 mol (as you can see, the grams canceled out)
        55.845 g/mol

Now, we use the definition: 1 mol = 6.022 x 10^23 atoms

1 mol                                            .000268 mols
----------------------------               =   -------------------------
6.022 x 10^23 atoms                     x atoms

Cross multiply, etc.: x = (.00268)*(6.022 x 10^23)/1 = 1.6 x 10^20

Of course, I've only been enrolled in a chemistry course for one week, so take all of this with a grain of salt!!!!

[rosario2468]

awesome thanks it make sooo much sense yay!!!!

[Borek]

Please read forum rules. Both of you.