Question

How many atoms are in 3.5 grams of silicon?

Answer 1

`=7.505xx10^22` atoms. (rounded to third place of decimal)

Explanation:

Average atomic weight of Silicon, Si atom is `28.0855` units.

We know from Mole concept that `1` mole is `6.022xx10^23` of anything. This number is called Avogadro's number.

Also that `1` mole of Silicon weighs `28.0855` g.

Therefore,
`28.0855` g of Silicon contains `6.022xx10^23` of Silicon atoms.
`3.5` g of Silicon contains number of atoms `=(6.022xx10^23)/28.0855xx3.5`
`=7.505xx10^22` atoms. (rounded to third place of decimal)