E. A student used a carbon pencil to write his homework. The mass of this was found to be 5 mg. With the help of this calculate.

Question

4) solve problems

E. A student used a carbon pencil to write his homework. The mass of this was found to be 5 mg. With the help of this calculate.

a. The number of moles of carbon in his homework writing

b. The number of carbon atoms in 12 mg of his homework writting

Answer 1

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=$\frac{massofsubstance}{molarmassofsubstance}$  

=$\frac{5\times {10}^{-3}g}{12gmo{l}^{-1}}$ 

= 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 =$\frac{massofsubstance}{molarmassofsubstance}$ 

=$\frac{12\times {10}^{-3}g}{12gmo{l}^{-1}}$ 

=1$\times {10}^{-3}$ mol 

$\therefore$ number of atoms of carbon =number of moles$\times$ avogadros constant

=$1\times {10}^{-3}\times 6.022\times {10}^{23}$ 

=$6.022\times {10}^{20}$  atoms