Is there a formula to do this based on an objects mass or density?
2007-01-29 01:54:21 · 7 answers · asked by Anonymous in Science & Mathematics ➔ Physics
Actually, there is. You need the molecular mass(molar mass) of the substance, and you find the mass of the object. Then you simply divide the mass by the molar mass, which gives you the moles of molecules of substance in that object. After that, you multiply the number by Avogadro constant, which is 6.02 x 10^23. This will give you the number of molecules in an object. Sadly, this is only true for pure substances. For impure substances, you need to find the percentage composition of the substance, then obtain the average molar mass, then the rest is the same.
2007-01-29 02:07:54 · answer #1 · answered by Harappy 1 · 0⤊ 0⤋
If you know the mass of the object and the molecular weight of the molecules (only one type) of which the object is constituted and hence the mass of the molecule, we can obtain the number of molecules by dividing the mass of the object by the mass of the molecule.
2007-01-29 10:06:20 · answer #2 · answered by Anonymous · 0⤊ 0⤋
If you have the mass, and you know the chemical make-up you can determine the number of molecules. You need to determine the atomic weight then use the atomic weight to determine the number of moles (ie. 1 mole of Al = 26.98g). The use the number of moles to determine the number of molecules (ie. 1 mole = 6.022 x 10^23). For complex composition the molecular weight easy. For example Al203 (aluminum oxide) the molecular weight is 2 time the Al weight + 3 times the O weight. For physical mixtures it is still a matter of the percent of each element.
2007-01-29 10:08:11 · answer #3 · answered by Shanna J 4 · 0⤊ 0⤋
Yes if you know the weight of the molecules. Just divide the weight of the object by the weight of the molecules.
Example: 1 kg of water.
The weight of the molecules of water is 18g per moles (6.022 x 10^23 molecules). So 1000 g has 55 moles or
1 kg of water holds
3.34 x 10^25 molecules of water.
2007-01-29 10:07:20 · answer #4 · answered by catarthur 6 · 0⤊ 0⤋
yeah, but you need to know what the object is made of.
Find out how many moles of molecule/ formula units using the molar weight then multiply by 6.02 * 10^23.
ex. A graphite for a mechanical pencil (still called lead) of 0.1g
graphite is carbon which is 12g/mol (find on the periodic table)
0.1g/(12g/mol) = .0083 moles
0.0083mole *6.02 * 10^23 = about 5 *10^21atoms
what is the object made of?
2007-01-29 10:10:18 · answer #5 · answered by Cindy B 5 · 0⤊ 0⤋
Avogadro's number is used to determine the number of molecules in a given mass.
2007-01-29 10:46:42 · answer #6 · answered by Kes 7 · 0⤊ 0⤋
You need to know the mass of the object and the composition.
number of moles = mass/molecular weight
[moles]= [m]/[m/mol]
2007-01-29 10:04:09 · answer #7 · answered by poseidenneptune 5 · 0⤊ 0⤋