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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

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Given : 

mass of carbon = 5mg =5×103g 

Atomic mass of carbon=12u 

Solution ::

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

 number of moles=mass of substancemolar mass of substance  

=5×103g12g mol1 

= 4.167×104mol 

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

mass of carbon =12mg =12×103g 

number of moles =mass of substancemolar mass of substance 

=12×103g12g mol1 

=1×103 mol 

 number of atoms of carbon =number of moles× avogadros constant

=1×103×6.022×1023 

=6.022×1020  atoms

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