Question

Estimate the number of electrons in 100g 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

Answer 2

no. of moles of water =given mass / molar mass = 100/18 = 50/9 moles

total no. of atoms in 100g of water = 6.022 *1023 * 50/9 = 3.455 *1024 atoms

no. of electrons in 1 atom of H2O = 2*1 +8 = 10

total no. of elctrons = 3.455*1024 *10 = 3.455*1025 electrons..

charge in 1 electron = 1.6 *10-19

charge carried by 3.455*1025 electrons = 1.6*10-19 * 3.455*1025 = 5.528 * 106