Question

calculate the number of moles in the following
1) 18.066 * 10^21 atoms of SO2
2) 12.044 * 10^23 atoms of H2O

Answer 1

We know that :-

$\rm n = \dfrac{number \: of \: atoms}{N_A} \\ \\ \sf where : N_A = 6.022 \times {10}^{23} and \: n \: is \: number \: of \: moles$

Now , we will use the above formula to solve the given question.

1. Number of atoms of SO_2 = 18.066 × 10²¹

$\rm \implies n = \dfrac{18.066 \times {10}^{21} }{6.022 \times {10}^{23}}$

$\rm \implies n = \dfrac{18066 \times {10}^{21} }{6022 \times {10}^{23}}$

$\rm \implies n = \dfrac{3 \times {10}^{21} }{1 \times {10}^{23}}$

$\rm \implies n = 3 \times {10}^{21 - 23}$

$\rm \implies n = 3 \times {10}^{ - 2}$

Number of moles = 3 × 10^(-2)

2) Number of atoms of H2O = 12.044 × 10²³

$\rm \implies n = \dfrac{12.044 \times {10}^{23} }{6.022 \times {10}^{23}}$

$\rm \implies n = \dfrac{12044 \times {10}^{23} }{6022 \times {10}^{23}}$

$\rm \implies n = \dfrac{2 \times {10}^{23} }{1 \times {10}^{23}}$

$\rm \implies n = 2$

Number of moles = 2

Answer :

1. 3 × 10^(-2)
2. 2

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Additional-Information :-

If mass and molar mass of an element/ compound is known then we can find number of moles by using the following formula :-

$\rm \implies n = \dfrac{m}{w}$

Where :-

• n = number of moles

• m = mass

• w = molar mass