Passing 21 600 C through aqueous silver nitrate deposits 24.17 g of silver ( $A_r = 108$ ). Taking the electronic charge as $1.6 \times 10^{-19}\ C$ , the Avogadro constant, in $mol^{-1}$ , is

9.65 \times 10^{23}

1.35 \times 10^{24}

3.01 \times 10^{23}

6.03 \times 10^{23}

Explanation: Moles of electrons = moles of Ag =

24.17/108 = 0.224

. Number of electrons =

21600/(1.6 \times 10^{-19}) = 1.35 \times 10^{23}

, so

N_A = 1.35 \times 10^{23}/0.224 = 6.03 \times 10^{23}

Derived from ZIMSEC Chemistry Paper 2, November 2002, Q3

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