Question

About how many electrons are in 30 grams of water (H2O)?

Answer 1

Hydrogen (H) has a molar mass of about 1.007 g/mol and has 1 electron.

Oxygen (O) has a molar mass of about 15.999 g/mol and has 8 electrons.

Then water (H₂O) has a total molar mass of about 18.015 g/mol and has 10 electrons.

30 g of water is the mass of

(30 g) × (1/18.015 mol/g) ≈ 1.66528 mol

of water. Recall that 1 mole is around 6.022 × 10²³ molecules (i.e. Avogadro's number). So 30 g of water is the mass of approximately 1.00285 × 10²⁴ molecules of water.

If each molecule contains 10 electrons, then 30 g of water contains 1.00285 × 10²⁵ ≈ 10²⁵ electrons.