### 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

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

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