Question

The number of molecules present in 200 g of baking soda is:

• A. $1.43\times {10}^{24}$
• B. $2.86\times {10}^{24}$
• C. $1.01\times {10}^{28}$
• D. $5.05\times {10}^{27}$

Answer 1

The correct option is A $1.43\times {10}^{24}$

The chemical formula of baking soda is ${\text{NaHCO}}_3$
Given mass = 200 g
Avogadro number = $6.022\times {10}^{23}$
Molar mass of ${\text{NaHCO}}_3$ = Atomic mass of sodium + Atomic mass of hydrogen + Atomic mass of carbon + 3$\times$ Atomic mass of oxygen
= 23 + 1 + 12 + 3 x 16
= 84

Number of molecules of sodium bicarbonate = Number of moles $\times$ Avogadro number ...(i)
Also, number of moles of sodium bicarbonate = $\frac{\text{Mass in gram}}{\text{Molar mass}}$ ....(ii)

Inserting equation (ii) in equation (i) we get

Number of molecules of sodium bicarbonate= $\frac{\text{Mass in gram}}{\text{Molar mass}}\times \text{Avogadro number}$...(iii)
Inserting values of mass, Avogadro number and molar mass in equation (iii) we get
Number of molecules of sodium bicarbonate = $\frac{200}{84}\times 6.022\times {10}^{23}$
Number of molecules of sodium bicarbonate
= $2.38\times 6.022\times {10}^{23}=1.43\times {10}^{24}$