Calculating number of moles from mass and volume — lesson. Science State Board, Class 10.

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1.	Calculate the number of moles in $46$ $g$ of sodium.

Data:

Given mass of sodium

$= 46$

$g$

Atomic mass or mass number of sodium

$= 23$

Formula:

The formula to find the number of moles from the mass is,

$Number of moles = \frac{Mass of the element}{Atomic mass of the element}$

Solution:

By substituting the values in the above formula, we get,

$\begin{array}{l} Number of moles & = & \frac{46}{23} \\ = & 2 \end{array}$

Hence, the number of moles in

$46$

$g$ of sodium

$=2$

$moles$

2.	Calculate the number of moles in $5.6$ $L$ of oxygen at STP.

Data:

Given volume of oxygen

$= 5.6$

$L$

Molar volume of oxygen at STP

$= 22.4$

$L$

Formula:

The formula to find the number of moles from the volume is,

$Number of moles = \frac{Given volume of O_{2} at STP}{Molar volume at STP}$

Solution:

By substituting the values in the above formula, we get,

$\begin{array}{l} Number of moles & = & \frac{5.6}{22.4} \\ = & 0.25 moles \end{array}$

Hence, the number of moles in

$5.6$

$L$ of oxygen at STP

$=0.25$

$moles$

3.	Calculate the number of moles of a sample that contains $12.046\times10^{23}$ atoms of iron.

Data:

Given the number of atoms of iron

$=12.046\times10^{23}$

Avogadro's number

$=6.023\times10^{23}$

Formula:

$Number of moles = \frac{Number of atoms of iron}{Avogadro number}$

Solution:

$\begin{array}{l} Number of moles & = & \frac{12.046 \times 10^{23}}{6.023 \times 10^{23}} \\ = & 2 \end{array}$

Hence, the number of moles of a sample that contains

$12.046\times10^{23}$ atoms of iron

$=2$

$moles$

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3. Calculating number of moles from mass and volume

Theory: