### Question 1.33

NCERT Class XI Chemistry

Calculate the number of atoms in each of the following (i) 52 moles of Ar (ii) 52 u of He (iii) 52 g of He.

### Video Explanation

(detailed solution given after this video)

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### Solution in Detail

$\displaystyle \underline{\underline{\text{(i) 52 moles of Ar}}}$

by def., 1 mol Ar contains $\displaystyle 6.023 \times 10^{23}$ atoms

$\displaystyle \therefore$ 52 mol contains $\displaystyle 52 \times 6.023 \times 10^{23}$ atoms

$\displaystyle = 3.132 \times 10^{25}$ atoms Ans!

$\displaystyle \underline{\underline{\text{(ii) 52 u of He}}}$

atomic mass of He is 4u

$\displaystyle \therefore$ 4u He contains 1 atom

Hence, 52u He contains $\displaystyle \frac{1}{4} \times 52 = 13$ atoms

$\displaystyle \underline{\underline{\text{(iii) 52g of He}}}$

Molar mass of He = 4 g

$\displaystyle \therefore $ 4g He contains 1 mol atom

Hence 52 g contains $\displaystyle \frac{1}{4} \times 52 = 13$ mol atom

$\displaystyle = 13 \times 6.02 \times 10^{23} = 7.826 \times 10^{24}$ atoms Ans!

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