Question

A 40.15 gram sample of a hydrate of Na2SO4 was heated thoroughly in a porcelain crucible, until its weight remained constant. After heating, 21.27 grams of the anhydrous compound remained. What is the formula of the hydrate?

Answer 1

Answer:

The formula of the hydrate of the sodium sulfate is :$Na_2SO_4.7H_2O$

Explanation:

Mass of hydrated sodium sulfate = 40.15 gram

Mass of completely dehydrated sodium sulfate = 21.27 gram

Mass of water molecules present in hydrated sodium sulfate =x

40.15 gram =  21.27 gram + x (Law of conservation of mass)

x  = 40.15 gram - 21.27 gram = 18.88 g

Moles of water = $\frac{18.88 g}{18 g/mol}= 1.04mol$

Moles of sodium sulfate =$\frac{21.27 g}{142.04 g/mol}=0.1497 mol$

Whole number ratio of sodium sulfate and water:

Sodium sulfate =$\frac{0.1497 mol}{0.1497 mol}=1$

Water =$\frac{1.04 mol}{0.1497 mol}=6.9 a\\rox 7$

The formula of hydrate be $Na_2SO_4.7H_2O$

So, the formula of the hydrate of the sodium sulfate is :$Na_2SO_4.7H_2O$