Question

If the molar volume of KCl and NaCl are x mL and y mL respectively, then the ratio of the edge length of FCC unit cells of KCl and NaCl will be​

Answer 1

The ratio between KCl and NaCl radii is 1.108

Option (B) is correct.

Explanation:

Correct statement:

The molar volume of KCl and NaCl is 37.46 ml and 27.94  ml. The ratio of unit cell edges of the two crystals is:

(1) 1.296  (2) 1.116  (3) 1.341  (4) 0.950

Solution:

The formula of Molar volume = N 4 / 3πr^3

• Where N is the Avogadro's  number  
• Now Molar volume of KCl is 37.46cm³

Put the values in the formula.

N 4 / 3 π R^3 = 37.46 cm³  

On solving the above equation we get

R = 2.458 x 10^-8 cm

Now for NaCl by using the same formula we get

R = 2.22 x 10^-8 cm

The ratio of edge length =   Ratio of radii of KCl / Ratio of radii of NaCl

The ratio of edge length = 2.458 / 2.22= 1.108

Thus the ratio between KCl and NaCl radii are 1.108