Question

9. Estimate the number of electrons in 100 g of water. How
much is the total negative charge on these electrons ?​

Answer 1

Weight of water = 100g

molecular weight of water = 18g/mol

∴ number of mole of water = given weight/molecule weight

= 100/18 = 5.55 moles

∵ 1 mole of water contains = 10 mole of electrons [ H₂O , 2 electrons of H and 8 electrons of O ]

∴ 5.55 moles of water contain 10 × 5.55 = 55.5 mole of electrons.

Now, number of electrons = number of mole of electrons × Avogadro's number

= 55.5 × 6.023 × 10²³

= 334.27 × 10²³

= 3.3427 × 10²⁵

Hence, number of electrons = 3.34 × 10²⁵

∵ charge on each electron = -1.6 × 10⁻¹⁹C

∴ total charge = number of electrons × charge on each electron

= 3.34 × 10²⁵ × 1.6 × 10⁻¹⁹ C

= 5.348 × 10⁶ C

Hence, total charge = 5.348 × 10⁶C