Q.15 g of a compound `Na_2SO_4.xH_2O`contains `2.36 * 10^23`molecules of water.Find the value of x.
According to the law of Avogadro 1mol of water contains `6.022xx10^23` molecules.
Molar mass of water `= 18g/(mol)`
Amount of water molecules present `= 2.36xx10^23`
Amount of water moles present `= (2.36xx10^23)/(6.022xx10^23)`
Amount of water moles present `= 0.392mol`
Mass of water moles `= 18xx0.392 = 7.054g`
Mass of `Na_2SO_4 = 15-7.054 = 7.946g`
Molar mass of `Na_2SO_4 = 142.043g/(mol)`
Amount of `Na_2SO_4 = 7.946/142.043 = 0.056mol`
`Na_2SO_4:H_2O = 0.056:0.392 = 1:0.392/0.056= 1:7`
`Na_2SO_4:H_2O = 1:x = 1:7`
So the value of x = 7