mole concept

some one plz also explain the above question also -difference between atomic weight and gram atomic weight.

prateek im talking about when C-12 came to light....you are right that many other elements like oxygen and nitrogen were chosen initially but im talking when it was confirmed that carbon has to be used as the reference element then at first that assumption was made....

NO initially u was defined as mass of 1/16 th of mass of one Oxygen atom.u is the mass of a binded proton in the nucleus also ..therefore altering u affects the universe also.

Atomic weight when expressed in grams is known as gram atomic weight.

prateek it is not at all creating a new universe ...u (atomic mass unit) was totally defined by scientists and it is not a thing that exists in real so that we can't define it as we want to ........rather, initially u was defined as 1/24th by mass of one C-12 atom by scientists but then it was defined as you know it now(ie 1/12 th by mass of .....) to increase the precision in the calculations ......so even if you define u in some other way there would be no change in universe but there would be just a change in the value of atomic mass unit and thus there wud be change in atomic masses of elements ...for eg if you take a new unit in place of atomic mass unit.say 'nu' which is 1/24 by mass of C-12 atom......then the atomic weight of all the elements would become twice of that which is now(for eg atomic weight of hydrogen wud be 2 nu rather than 1 u)
and yes
N0 u = 1gram
so .. u = 1/N0 gram..and is the mass of a proton..
value of u is like this because it is defined that way ...u define it some other way ...no change in universe ......u is not like mass of an electron(or mass of anything) which has to be same as it exists

gram at wt: The atomic weight of an element expressed in grams, that is, the atomic weight on a scale on which the atomic weight of carbon-12 isotope is taken as 12 exactly.

at wt: Ratio of the average mass of a chemical element's atoms to ¹⁄₁₂ the mass of an atom of the carbon-12 isotope.

gram atomic weight is the number of moles

another question

Q-1 In what ratio by mass are O,O₂ and O₃ present in 50 gm of pure CuSo₄.5H₂O ?

ok guys here's the question due to which i asked this question:

Q-1 What will be the change in value of (i)atomic weight and (ii) gram atomic weight of any element if

(a) value of Na(avogadro no) becomes 10 times ie 10Na

(b) value of u/amu (ie 1/12th by part mass of one atom of C-12 isotope)is
made equal to 1/9th by part mass of one atom of C-12 isotope.

@.......................
no of moles ????
are u sure??
i dont think so

Atomic weight, mean (weighted average) of the masses of all the naturally occurring isotopes of a chemical element, as contrasted with atomic mass, which is the mass of any individual isotope.
Gram-atomic weight, amount of an atomic substance whose weight, in grams, is numerically equal to the atomic weight of that substance.
Eg - 1 gram atomic weight of atomic oxygen is 16 grams(atomic weight).