JEE MAIN - Chemistry (2021 - 1st September Evening Shift - No. 18)
The number of atoms in 8g of sodium is x $$\times$$ 1023. The value of x is ____________. (Nearest integer)
[Given : NA = 6.02 $$\times$$ 1023 mol$$-$$1
Atomic mass of Na = 23.0 u]
[Given : NA = 6.02 $$\times$$ 1023 mol$$-$$1
Atomic mass of Na = 23.0 u]
Answer
2
Explanation
Given, mass of Na = 8g
Molar mass of Na = 23 gmol$$-$$1
$${{Weight\,of\,sodium\,atom} \over {Molecular\,mass\,of\,sodium\,atom}} = {{Number\,of\,atoms} \over {Avogadro's\,number}}$$
$${{8g} \over {23g}} = {{Number\,of\,atoms} \over {6.022 \times {{10}^{23}}}}$$
Number of atoms $$ = {{8 \times 6.022} \over {23}} \times {10^{23}}$$
Number of atoms = 2.09 $$\times$$ 1023
x $$\approx$$ 2
Hence, answer is 2.
Molar mass of Na = 23 gmol$$-$$1
$${{Weight\,of\,sodium\,atom} \over {Molecular\,mass\,of\,sodium\,atom}} = {{Number\,of\,atoms} \over {Avogadro's\,number}}$$
$${{8g} \over {23g}} = {{Number\,of\,atoms} \over {6.022 \times {{10}^{23}}}}$$
Number of atoms $$ = {{8 \times 6.022} \over {23}} \times {10^{23}}$$
Number of atoms = 2.09 $$\times$$ 1023
x $$\approx$$ 2
Hence, answer is 2.
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