# Calculate the number of electrons which will together weigh one gram

Question.

(i)Calculate the number of electrons which will together weigh one gram.

(ii)Calculate the mass and charge of one mole of electrons

Solution:

(i) Mass of one electron $=9.10939 \times 10^{-31} \mathrm{~kg}$

$\therefore$ Number of electrons that weigh $9.10939 \times 10^{-31} \mathrm{~kg}=1$

$\therefore$ Number of electrons that will weigh $1 \mathrm{~g}\left(1 \times 10^{-3} \mathrm{~kg}\right)$

$=\frac{1}{9.10939 \times 10^{-31} \mathrm{~kg}} \times\left(1 \times 10^{-3} \mathrm{~kg}\right)$

$=0.1098 \times 10^{-3+31}$

$=0.1098 \times 10^{28}$

$=1.098 \times 10^{27}$

(ii) Mass of one electron $=9.10939 \times 10^{-31} \mathrm{~kg}$

Mass of one mole of electron $=\left(6.022 \times 10^{23}\right) \times\left(9.10939 \times 10^{-31} \mathrm{~kg}\right)$

$=5.48 \times 10^{-7} \mathrm{~kg}$

Charge on one electron $=1.6022 \times 10^{-19}$ coulomb

Charge on one mole of electron $=\left(1.6022 \times 10^{-19} \mathrm{C}\right)\left(6.022 \times 10^{23}\right)$

$=9.65 \times 10^{4} \mathrm{C}$

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