Question

Barium chloride crystals contain 14.8% waterof crystallisation. Find the number of molecules of water of crystallysation per molecule.

Answer 1

BaCl2. n H2O
Ba atomic mass=137
Cl atomic mass=35.5
molecular mass of water = 18
14.8% water means
14.8g of water in 100 g of BaCl2. n H2O
n x18 g water will be there in [137+71+n(18)]g of BaCl2. n H2O
1800xn = 14.8[208+n18]
1800n-266.4n=3078.4
1533.6n =3078.4
n= 2.0073
we can take n=2

Answer 2

Answer : The number of molecules of water of crystallization per molecule is, 2

Explanation : Given,

Barium chloride crystals contain 14.8% water of crystallization.

Molar mass of barium chloride = 208 g/mole

Molar mass of water = 18 g/mole

Let the number of molecules of water of crystallization per molecule be, 'x'

The formula becomes, $BaCl_2.xH_2O$

Now we have to calculate the number of molecules of water of crystallization per molecule.

$\%\text{ composition of water}=\frac{\text{Mass of water}}{\text{Mass of }BaCl_2}+{\text{Mass of water}}\times 100$

Now put all the given values in this formula, we get

$14.8=\frac{18x}{208}+{18x}\times 100$

$x=2$

The formula becomes, $BaCl_2.2H_2O$

Therefore, the number of molecules of water of crystallization per molecule is, 2