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Calculate the value of Avogadro numberfrom the internuclear distanceof adjacent ions in NaCl, 0.282 nm and the densityof solid NaCl is 2.17xx10^(3)kg//m^(3) . A unit cell contains 4 NaCl formulaunits.

Answer»

Solution :To calculate the Avogadro constant, that is, NUMBER of NaCl formula UNITS per mole, let us take 1 mole of NaCl.
Volume of 1 mole of NaCl `=("mass of 1 mole")/("density")`
`=(58.5 xx 10^(-3))/(2.17 xx 10^(3)) = 2.7 xx 10^(-5) m^(3)`
Volume of 1 unit cell `=a^(3) = (0.564 xx 10^(-9))^(3) = 1.79 xx 10^(-28) m^(3)`
`therefore` number of unit cell per mole `=(2.7 xx 10^(-9))/(1.79 xx 10^(-28)) = 1.51 xx 10^(23)`
Since 1 unit cell of NaCl has 4 NaCl formula units, Avogadro constant (formula units per mole) `=4 xx (1.51 xx 10^(23))`
`=6.04 xx 10^(23)`


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