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Asked in GSEB Board August 2020 · Properties of charge
Given: 180 g of water; molar mass of H₂O=18 g mol⁻¹; N_A=6.02×10²³ mol⁻¹.
Moles: n=(180)/(18)=10 mol, so the number of molecules is 10×6.02×10²³=6.02×10²⁴.
Each molecule has 2 protons in its hydrogen atoms and 8 in its oxygen atom: 10 protons per molecule.
Protons: 6.02×10²⁴×10=6.02×10²⁵
Positive charge: Q=6.02×10²⁵×1.6×10⁻¹⁹=9.63×10⁶ C=0.963×10⁷ C
(Some keys give 1.34×10⁷ C; that is the value for a 250 g cup, not for 180 g.)
The electrons carry an equal negative charge, which is why the cup is neutral overall.
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