Question

What is the number of molecules of 140 g of CO?

Answer 1

A mole is a quantity that denotes 6.022$\times {{10}^{23}}$atoms or we can say molecules or particles, also called Avogadro number. Every 1 mole of an element contains this number of atoms. CO is a compound called carbon monoxide; its molar mass is the sum of atomic mass of carbon, that is 12 and oxygen, that is 16.

Complete answer:
We have been given a quantity of carbon monoxide, CO, which is 140 g. we have to find the number of molecules in this quantity of carbon monoxide.
For this the molar mass of CO, is calculated which is the sum of atomic mass of C and O, as
Mass of CO = atomic mass of (C + O)
Mass of CO = 12 + 16
Mass of CO = 28 g/mol
Now, we have to calculate the number of moles that 140 g of CO consist, for this number of moles formula is used, which is,
Number of moles = $\dfrac{given\,mass}{molar\,mass}$ , give mass is 140 g, and molar mass is 28 g/mole
Number of moles of CO = $\dfrac{140g}{28\,g\,mo{{l}^{-1}}}$
Number of moles of CO = 5 moles
Now, to find the number of molecules in 5 moles of CO, we will multiply these 5 moles with Avogadro's number as,
Molecules in CO = $5\times 6.022\times {{10}^{23}}$
Molecules in CO =$3.02\times {{10}^{24}}$
Hence, 140 g of CO has $3.02\times {{10}^{24}}$molecules.

Note:
Irrespective of 140 g which are 5 moles of carbon monoxide, if we take the amount or moles of any element, then the total number of atoms in that amount of element will always be the amount of element multiplied by the Avogadro number of atoms per mole (6.022$\times {{10}^{23}}$)