A crystal containing 11.7 g of NaCl (molar mass 58.5 g mol^-1) has one Schottky pair for every 10^6 formula units. Taking N_A = 6.022x10^23 mol^-1, find the number of Schottky pairs in the crystal in units of 10^17 (two decimals).

JEE Main levelNumerical answerDifficulty 2 of 3ss190

A crystal containing $11.7 g$ of $NaCl$ (molar mass $58.5 g mo l^{- 1}$ ) has one Schottky pair for every $1 0^{6}$ formula units. Taking $N_{A} = 6.022 \times 1 0^{23} mo l^{- 1}$ , find the number of Schottky pairs in the crystal in units of $1 0^{17}$ (two decimals).

Numerical answer type, answer in x10^17, tolerance 0.01.

Moles of NaCl

= 11.7/58.5 = 0.2

. Formula units

= 0.2 \times 6.022 \times 1 0^{23} = 1.2044 e + 23

. Pairs

= 1.2044 e + 23 \times 1 0^{- 6} = 1.2044 \times 1 0^{17}

, i.e.

1.2 \times 1 0^{17}