If we know the mass of an object can we know the exact number of atoms present in the object?

Question

If we know the mass of an object can we know the exact number of atoms present in the object?( even the composition of the object)

is there any way to calculate the number of atoms ,, if we know the mass of the object..

lets take an example of Moon...

how many atoms will it have?

Answer 1

You can if you knew all the individual compounds and elements that make it and the amount. In chemistry, you will learn that the atomic number of an element in grams is one mole of the element, which has exactly 6.022 x 10^23 atoms. molecular/formula mass in grams is one mole of that compound, with 6.022 x 10^23 molecules of that compound. this number 6.022 x 10^23 is Avogadro's number, or NA (A is the subscript).



Now, relating to mass, to find number of moles (n), given a mass of an element or compound, we say n = given mass of substance/ Molar mass of substance. the molar mass is the sum of all the masses of the elements in the substance i.e H2O is (1 x 2) + 16 as H has a mass of 1 and O has a mass of sixteen, using a periodic table.



Then if you have n, Number of atoms or molecules = n lots of avogadro's number.



Eg. find the number of molecules of water in 18g of water.

number of moles = 18/ (1 x 2 + 16)

= 1



No. atoms/molecules = 1 x 6.022 x 10^23 = avogadro's bumber of molecules.



You would need to repeat this for each element/compound you find and know their masses for the moon.

Answer 2

Yes we can approximate only if we know how much atoms (including those in molecules) there are in the mass.



Example, how many atoms are there in 1 kg of water there are 3.345634328x10²⁵ atoms. But still this is an approximate.



It's already too difficult to determine the exact shape of the moon let alone trying to figure out what materials the moon is made up of. So it wouldn't be possible to calculate the EXACTLY number of atoms!



Look up Avogadro's Number, it relates the atomic mass and number of atoms/molecules. If you know the atomic mass you can calculate the number of atoms.

Answer 3

Exactly, no.

Let's say I have a box that weighs 238 amu (atomic mass units).

How many atoms are in it?

If it's helium atoms, then the atomic weight is 1 amu, 238 atoms.

If it's uranium atoms, then the atomic weight is 238 amu, 1 atom.

If I don't know what it's made up of then it could be anywhere from 1 to 238 atoms in the box.

The moon is made up of a bunch of different atoms: iron, nickel, silicon, magnesium, etc. in various proportions. You can get an average number but not an exact number without more information.

Answer 4

no we cannot calculate because everything in the universe is a mixture of several elements. so to calculate the number of atoms of each element we should also know the elements that are present, mass of the elements. if we are able to make the empirical of the given substance we could approximately calculate number of atoms of diff elements. its just an approximation because there will dust particles, so the sample of the material has to be refined

Answer 5

just knowing mass, we can not find the number of atoms present in the object. there are so many other things need to be known for this!!!