Some Basic Concepts of Chemistry - Result Question 3
####6. If Avogadro number $N_A$, is changed from $6.022 \times 10^{23} mol^{-1}$ to $6.022 \times 10^{20} mol^{-1}$ this would change :
[2015 RS]
(a) the definition of mass in units of grams
(b) the mass of one mole of carbon
(c) the ratio of chemical species to each other in a balanced equation.
(d) the ratio of elements to each other in a compound
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Solution:
(b) If $6.022 \times 10^{23}$ changes to $6.022 \times 10^{20} / mol$ then this would change mass of one mole of carbon.
Mass of $ _{12} C$ carbon is used to define the atomic mass unit. In this system, $12 C$ is assigned a mass of exactly 12 a.m.u.
Earlier one mole was defined as the amount of substance that contains as many particles as there are atoms in exactly $12 g$ of the $ _{12} C$ isotope. From November 2018, one mole is defined as exactly $6.02214076 \times 10^{23}$ constitutive particles, which may be atoms, molecules, ions or electrons.
Hence, if we change the value of NA from $6.022 \times$ $10^{23} mol^{-1}$ to $6.022 \times 10^{20} mol^{-1}$ then mass of one mole of carbon will also change.
The definition of mass is independent of Avogadro number $N_A$.
(3) Molecules of water $=$ mole $\times N_A=10^{-3} N_A$
