Question

Calculate the number of moles in $179g{\text{ }}of{\text{ }}{H_2}{O_2}$

Answer 1

Number of moles of a substance is defined as mass of given substance divided by the molar mass of the substance.
Number of moles of given substance $= \dfrac{{Given\,weight\,of\,subs\tan ce}}{{molecular\,weight}}$

Complete step by step answer:
The mass of a substance that consists of the equal quantity of the basic units is known as mole. For example: the atoms in 12gm is equal to the 12C.
To calculate the number of moles of $\left( {{H_2}{O_2}} \right)$, first we have to calculate molar mass or molecular weight of $\left( {{H_2}{O_2}} \right)$
What is molecular weight?
It is defined as the total mass of each atom in that compound. The mass of the given substance is divided by the amount of the substance. Molecular weight is also known as molar mass.
Given: weight of ${H_2}{O_2} = 179g$
To find the molecular weight of hydrogen peroxide $\left( {{H_2}{O_2}} \right)$
Molecular weight of ${H_2}{O_2} = \left[ {2 \times atomc{\text{ }}mass{\text{ }}of{\text{ }}hydrogen{\text{ }}atom\left( H \right) + 2 \times atomic{\text{ }}mass{\text{ }}of{\text{ }}Oxygen{\text{ }}atom\left( O \right)} \right]$
Where, atomic mass of hydrogen atom$= 1g/mol$, Atomic mass of Oxygen atom $= 16g/mol$
Then molecular weight of hydrogen peroxide $\left( {{H_2}{O_2}} \right) = \left[ {2 \times 1 + 2 \times 16} \right]$
$= \left[ {2 + 32} \right]$
$= 34g/mol$.
By using the formula:
Number of moles of hydrogen peroxide $\left( {{H_2}{O_2}} \right) = \dfrac{{Given\,weight\,of\,{H_2}{O_2}}}{{Molecular\,weight\,of\,{H_2}{O_2}}}$
Now, putting the value of weight of hydrogen peroxide and molecular weight of hydrogen peroxide, we get
$\Rightarrow$Number of moles of hydrogen peroxide \left( {{H_2}{O_2}} \right)$$$ = \dfrac{{179}}{{34}}$$ Therefore, the number of moles of hydrogen peroxide \left( {{H_2}{O_2}} \right)$is$5.265\,moles.$

Additional Information: Mole of a substance always contains the same number of particles, whatever the substance may be.
1 mole$= 6.02314 \times {10^{23}}$particles.
Example: 1mole of $O$ atoms means, there are $6.02314 \times {10^{23}}$ number of oxygen atoms are present.
1 mole of ${O_2}$ molecules means there are $6.02314 \times {10^{23}}$ number of oxygen molecules present.
Here, number of oxygen atoms $= 2 \times 6.02314 \times {10^{23}} \Rightarrow 12.04628 \times {10^{23}}$(as 1 molecule of oxygen contain 2 atoms of oxygen).

Note:
Mole is simply a unit for counting entities at the microscopic level (i.e. atoms, molecules, particles, electrons, ions, etc.), just as we use one dozen for twelve objects and one score for twenty objects. In SI system, mole (symbol: mol) was introduced as the seventh base quantity for the amount of a substance. In other words, mole is the amount of substance that contains as many atoms, molecules, ions or other particles as there are atoms in $12g$of Carbon ${C^{12}} -$isotope.