How many atoms in sample?

[s3a]

I do not know how to do the following question:

Potassium permanganate, KMnO4, is a dark purple crystalline solid used as an antiseptic, and in deodorizers and dyes.

a) How many potassium atoms are there in a 7.238g sample of KMnO4?
b) How many oxygen atoms are there in the above sample?

Answer for a): 2.758*10^22 K atoms
Answer for b): 1.103*^23 O atoms

Any help would be greatly appreciated!
Thanks in advance!

[Sodapop]

I do not know how to do the following question:

Potassium permanganate, KMnO4, is a dark purple crystalline solid used as an antiseptic, and in deodorizers and dyes.

a) How many potassium atoms are there in a 7.238g sample of KMnO4?
b) How many oxygen atoms are there in the above sample?

Answer for a): 2.758*10^22 K atoms
Answer for b): 1.103*^23 O atoms

Any help would be greatly appreciated!
Thanks in advance!Always start by finding the molar mass of the substance you have:

Potassium (K) = 39.098
Manganese (Mn) = 54.938
Oxygen (O) = 15.999

(39.098) + (54.938) + 4(15.999) = 158.032 g/mol

Now that you have the molar mass, you can find the amount of atoms in your substance and compare it with the number of atoms of both potassium and oxygen.

[s3a]

For potassium I did:

158g/1mol = 7.238g/n

n = 0.0458mol

(0.0458mol)(6.022*10^23 atoms/mole)
= 2.759*10^22 K atoms

but for oxygen I am completely lost since I thought that the molar mass of the whole thing (KMnO4) would be the same as that of both Potassium and Oxygen however the answer for Oxygen is different! There are no coefficients in front of the elements in the chemical name so I have no idea what to do for Oxygen and now I am not too sure if I know how to find the amount of atoms for Potassium and I'm starting to think it was a numerical coincidence or something.

[Sonic]

The number of oxygen atoms will be 4/6 = 2/3 of the total number of atoms. If you've worked out how many atoms there are in total (moles * avogadro's number) then multiply this by 2/3

The 4/6 comes from the ratio of oxygen atoms to the total atoms. Mathematically: n(O)/n(t) where n(O) is number of oxygen and n(t) is total number.

As n(O) = 4 and n(t) = 6 we get 4/6 which cancels to 2/3.

[s3a]

(2/3)(2.758*10^22 K atoms) ≠ 1.103*10^23 O atoms

Plus, if Oxygen is (4/6) = (2/3) of the total chemical formula then wouldn't Potassium be (1/6) of the chemical formula itself? Because I assumed a 1:1 ratio because no matter how many moles of KMnO4 you have, the proportions of each element in the compound are proportional or at least that is my logic when doing the problem.