(solved)Question 2.1 of NCERT Class XI Chemistry Chapter 2

(i) Calculate the number of electrons which will together weigh one gram. (ii) Calculate the mass and charge of one mole of electrons.
(Rev. 04-Jun-2024)

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Question 2.1 NCERT Class XI Chemistry

(i) Calculate the number of electrons which will together weigh one gram. (ii) Calculate the mass and charge of one mole of electrons.

Video Explanation(detailed solution given after this video)

Please watch this youtube video for a quick explanation of the solution:

Solution in Detail

$\displaystyle \underline{\underline{\text{Part (i)}}}$

Mass of 1 electron = $\displaystyle 9.1 \times 10^{-31}$ kg

i.e., = $\displaystyle 9.1 \times 10^{-31} \times 1000 \text{ grams}$

i.e., = $\displaystyle 9.1 \times 10^{-28} \text{ grams}$

by unitary $\displaystyle 9.1 \times 10^{-28} \text{ g} \equiv$ 1 electron

$\displaystyle \implies 1 \text{ g} \equiv \frac{1}{9.1 \times 10^{-28}}$ electrons

$\displaystyle = 1.099 \times 10^{27} \text{ electrons}\:\underline{Ans}$

$\displaystyle \underline{\underline{\text{Part (ii)}}}$

1 mol electron = $\displaystyle 6.023 \times 10^{23}$ electrons

Mass of 1 electron = $\displaystyle 9.1 \times 10^{-31}$ kg

∴ of 1 mol = $\displaystyle 9.1 \times 10^{-31} \times (6.023 \times 10^{23})$ kg

= $\displaystyle 5.48 \times 10^{-7} \text{ kg} \:\underline{Ans}$

Charge on 1 electron = $\displaystyle 1.6 \times 10^{-19} \text{ C}$

∴ of 1 mol = $\displaystyle 1.6 \times 10^{-19} \times (6.023 \times 10^{23})$ C

= $\displaystyle 9.64 \times 10^{4} \text{ C} \:\underline{Ans}$