Given :
mass of carbon = 5mg =\(5\times 10^{-3} g\)
Atomic mass of carbon=12u
Solution ::
a. The number of moles of carbon in his homework writing
number of moles=\(mass \space of \space substance \over molar \space mass \space of \space substance\)
=\(5\times 10^{-3} g\over 12 g\space mol^{-1}\)
= 4.167\(\times 10^{-4} mol\)
b. The number of carbon atoms in 12 mg of his homework writting
mass of carbon =12mg \(=12\times 10^{-3} g\)
number of moles =\(mass \space of \space substance \over molar \space mass \space of \space substance\)
=\(12\times 10^{-3} g\over 12 g\space mol^{-1}\)
=1\(\times 10^{-3}\) mol
\(\therefore
\) number of atoms of carbon =number of moles\(\times \) avogadros constant
=\(1\times 10^{-3}\times 6.022\times10^{23}\)
=\(6.022\times 10^{20}\) atoms
