# What is the mass in grams of each of the following? a) 4.50 times 10^{12} atoms of Cl. b) 8.42...

## Question:

What is the mass in grams of each of the following?

a) {eq}4.50 \times 10^{12} {/eq} atoms of {eq}\rm Cl {/eq}.

b) {eq}8.42 \times 10^{18} {/eq} atoms of {eq}\rm Br {/eq}.

## Number of Moles

If we are given the amount of the total number of atoms of molecules, then the number of moles is calculated by the following formula:

{eq}\textrm{the number of moles}=\dfrac{\textrm{Total number of atoms or molescules}}{\textrm{Avogadro number}} {/eq}

As we are given the number of atoms of chlorine and bromine and asked to find their masses in gram. So, in order to find this, we will first find the number of moles and then find their masses by multiplying with their respective molar masses to obtain the desired result.

Part (a)

Number of atoms of chlorine = {eq}4.50 \times 10^{12} {/eq}

{eq}\begin{align} \textrm{Number of moles of chlorine atom}&=\dfrac{\textrm{Total number of atoms}}{\textrm{Avogadro number}}\\ &=\dfrac{4.50 \times 10^{12}}{6.022\times 10^{23}}\\ &= 7.47\times 10^{-12}\ mol\\ \therefore \textrm{Mass of chlorine atom in gram} &= \textrm{Number of moles }\times \textrm{Molar atomic mass}\\ &= 7.47\times 10^{-12}\ mol\times 35.5\ g/mol\\ &=2.65\times 10^{-10}\ g \end{align} {/eq}

Part (b)

Number of atoms of bromine = {eq}8.42 \times 10^{18} {/eq}

{eq}\begin{align} \textrm{Number of moles of bromine atom}&=\dfrac{\textrm{Total number of atoms}}{\textrm{Avogadro number}}\\ &=\dfrac{8.42 \times 10^{18}}{6.022\times 10^{23}}\\ &= 1.39\times 10^{-5}\ mol\\ \therefore \textrm{Mass of bromine atom in gram} &= \textrm{Number of moles }\times \textrm{Molar atomic mass}\\ &= 1.39\times 10^{-5}\ mol\times 80\ g/mol\\ &=1.12\times 10^{-3}\ g \end{align} {/eq}