DETERMINATION OF ATOMIC MASS

Dulong and petit's rule : It is based on experimental facts. "At ordinary temperature, product of atomic mass and specific heat for solid elements is approximately 6.4 and this product is known as atomic heat of the element"

Atomic mass × specific heat = 6.4

The law is valid for solid elements except Be, B, Si and C.

Correct At. mass = Eq. mass × valency

Specific heat method : This method is for gases.  , where Cp = specific heat at constant pressure and Cv = specific heat at constant volume. the ratio g is a constant = 1.66 for monoatomic, 1.40 for diatomic, 1.33 for triatomic gas and atomic mass of gaseous element

Chloride formation method : This method converts the element (whose mass is to be determined) into volatile chloride whose vapour density is found by Victor Mayer method.

Molecular mass = 2 × V.D.

Vapour density method is suitable for elements having volatile chlorides.

Atomic mass = Eq. mass of metal × valency.

Mitscherlich's law of isomorphism : It states that isomorphous substances have similar chemical constitution. Isomorphous substances form crystals of same shape and valencies of elements forming isomorphous salts are also same. eg: ZnSO4. 7H2O, MgSO4.7H2O and FeSO4.7H2O are isomorphous.