[DumbTwitchMain]

A question in the summer packet that's supposed to be 'review,' though we never learned this. Any explanation would be appreciated, as I'm having trouble finding one otherwise online.

EDIT: Answer, as provided in the teacher's key, is 17molFe, though I don't understand how this value could be higher than the sample...

[DumbTwitchMain]

When a sample of Chromium Oxide (Cr2O3) is found to have a mass of 12.07 g, how many Chromium atoms are present?

Answer, as provided in teacher's key, is 9.561 x 10^22 atomsCr - any explanation would be appreciated, as this was not taught to me last year in Honors Chem.

[DumbTwitchMain]

Aluminum Oxide, Al2O3, has a density of 3.95 g/cm3. Within a 4.0 m3 sample, how many Aluminum atoms are present?

Answer, as provided in teacher's key, is 1.9 x 10^29 atomsAl - any explanation would be appreciated, as (if you've read my other posts you'll see) this topic was not covered last year in Honors Chem.

[Borek]

I have merged all your three threads as they are almost identical. Please read the forum rules.

though we never learned this

You stated exactly the same in all three questions of yours, but I find it hard to believe - these are all trivial, basic conversions between mass, number of moles, and number of atoms.

Plenty of excellent resources on the web, see for example https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK-12)/10%3A_The_Mole

[Vidya]

AP Chem: How many moles of Iron are in 5.7 mol Fe3N2?

I can help you in planning -
Check how many moles of Fe are there in 1 mole of Fe3N2
In 1 molecule we have three atoms of Fe so in one more we will have three moles of Fe
Then use unitary method to get the number of moles of Fe  in Fe3N2

When a sample of Chromium Oxide (Cr2O3) is found to have a mass of 12.07 g, how many Chromium atoms are present?

or this question start with what is given to you-
12.07 g Cr2O3  moles of Cr2O3    moles of Cr    atoms of Cr
Now you should know how to convert grams into moles remember one mole is equal to molar mass of that substance in gram -use this conversion to get moles of Cr2O3 .From the formula of the compound with the moles of chromium atoms.You know that one mole is Avogadro's number of atoms .Use this relationship to convert the moles of chromium atom to number of atoms of chromium

Aluminum Oxide, Al2O3, has a density of 3.95 g/cm3. Within a 4.0 m3 sample, how many Aluminum atoms are present?

Density *Volume    mass Al2O3    moles of Al2O3      moles of Al                 
                                                                                                             atoms of Al
It is more like mathematics after understanding mole concept.Now try these questions.

[Fudjsk]

The numbers on the boxes of the elements in the periodic table have numbers.
These numbers symbolize the number of grams an Avogadro's number of this atom weighs (molar mass).
By adding them up you can find the molar mass of molecules.

For the problem, you could find the ratio between how much of it in grams, there is and the molar mass of this molecule. Then you could compare it to Avagadro's number to find the unknown amount of molecules.
However, keep in mind from there that the number that results is the number of molecules. Not the number of Chromium atoms.