Question

A Graphite pencil weighs $3.0\times {{10}^{-10}}$ .How many carbon atoms are present in it?
$\left( {{N}_{A}} = 6\times {{10}^{23}} \right)$
a.) $1.5\times {{10}^{13}}$
b.) $5\times {{10}^{12}}$
c.) $2\times {{10}^{33}}$
d.) $1.5\times {{10}^{10}}$

Answer 1

The basic knowledge of one mole of a substance and the mass and number of particles in one mole of a substance is required. Mole concept is to be used here.
- As graphite is an allotrope of carbon so its molar mass will be the same as that of carbon.
- The number of particles in one mole of any substance is a fixed number which is known as Avogadro constant.

Complete Solution :
So according to the above information,one mole of any substance is a constant which is the Avogadro number or constant whose value is given in the question.
Atomic mass of carbon is $12\,g$
As carbon is an element,so its atomic mass of graphite's atomic mass will be the same as the molar mass of the substance.

Given mass of graphite is $3.0\times {{10}^{-10}}g$
So now number of particles in $12\,g$ of graphite atom = Avogadro constant$\left( {{N}_{A}}=6\times {{10}^{23}} \right)$
$\Rightarrow$ now number of particles in $1\,g$ of graphite atom=$\dfrac{6\times {{10}^{23}}}{12}$
$\Rightarrow$ now number of particles in $3.0\times {{10}^{-10}}g$ of graphite atom = $\dfrac{6\times {{10}^{23}}}{12}\times 3\times {{10}^{-10}}$
$\Rightarrow 1.5\times {{10}^{13}}$ Particles
So, the correct answer is “Option A”.

Note: The mole concept helps to put quantitative information about what happens in a chemical equation on a macroscopic level.
- Like the number of particles, the volume occupied by one mole of substance at standard temperature and pressure is known as molar volume.
- Like graphite, diamond is also an allotrope of carbon.
- The electrons are free to move through the structure, so graphite can conduct electricity. This makes graphite useful for electrodes in batteries and for electrolysis. The layers in graphite can slide over each other because the forces between them are weak.