Question

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

Answer 1

Molecular mass of water= 18 g
Number of molecules in 18 g of H₂O = Avogadro's number 
                                                            = 6.023 × 10²³
Number of electrons in 1 molecule of H₂O = (2 × 1) + 8 = 10
Number of electrons in 6.023 × 10²³ molecules of H₂O = 6.023 × 10²⁴
That is, number of electrons in 18 g of H₂O = 6.023 × 10²⁴
So, number of electrons in 100 g of H₂O = \[\frac{6 . 023 \times {10}^{24}}{18} \times 100\]

                                                                 = 3.34 × 10²⁵
         ∴ Total charge = 3.34 × 10²⁵ × 1.6 × 10⁻¹⁹
                                 = 5.34 × 10⁶ C