Hydrated salt and anhydrous salt

A hydrated salt is a salt that contains water molecules within its crystal structure. Anhydrous salt is a salt that does not contain any water molecules.

Loss in weight on heating

When a hydrated salt is heated, it loses water molecules and becomes anhydrous. The loss in weight on heating is due to the loss of water molecules.

Calculation of n

The percentage loss in weight can be calculated using the formula:

% loss in weight = (initial weight - final weight) / initial weight x 100

Given that the hydrated salt undergoes a 55.9% loss in weight on heating, we can calculate the final weight as follows:

final weight = initial weight - (55.9 / 100) x initial weight
final weight = 0.411 x initial weight

Since the salt becomes anhydrous after heating, its final weight is equal to the weight of the anhydrous salt. Let the formula of the anhydrous salt be Na2SO4.

The molar mass of Na2SO4 is 142 g/mol.

The initial weight of the hydrated salt can be calculated by dividing its mass by the molar mass and multiplying by Avogadro's number:

initial weight = (mass / molar mass) x Avogadro's number
initial weight = (mass / 142) x 6.022 x 10^23

The final weight of the anhydrous salt can also be calculated by dividing its mass by the molar mass and multiplying by Avogadro's number:

final weight = (mass / molar mass) x Avogadro's number

Since the final weight is equal to 0.411 times the initial weight, we can equate the two expressions and solve for n:

(mass / 142) x 6.022 x 10^23 = 0.411 x (mass / 142) x 6.022 x 10^23 x (2 + n)

Simplifying this equation, we get:

2 + n = 10.0
n = 8.0

Therefore, the value of n is 8.0, which is closest to option D (10).