The aqueous aluminium sulfate formed is crystallised to make hydrated aluminium sulfate,Al 2 (SO4 ) 3 •xH 2 O.The relative formula mass of hydrated aluminium sulfate is 666.Calculate the value of x in the formula Al 2 (SO4 ) 3 •xH 2 O

To find the value of x in the formula Al2(SO4)3•xH2O, we first need to calculate the molar mass of Al2(SO4)3 and then subtract it from the given relative formula mass of the hydrated aluminium sulfate.

1. Calculate the molar mass of Al2(SO4)3:

   • Aluminium (Al) has an atomic mass of 27 g/mol. Since there are 2 aluminium atoms in the formula, the total mass contributed by aluminium is 2*27 = 54 g/mol.
   • Sulfur (S) has an atomic mass of 32 g/mol and oxygen (O) has an atomic mass of 16 g/mol. Since there are 3 sulfate ions (SO4) in the formula, the total mass contributed by sulfate is 3*(32 + 416) = 396 = 288 g/mol.
   • Therefore, the molar mass of Al2(SO4)3 is 54 + 288 = 342 g/mol.

2. Subtract the molar mass of Al2(SO4)3 from the given relative formula mass of the hydrated aluminium sulfate:

   • The given relative formula mass of the hydrated aluminium sulfate is 666 g/mol.
   • Subtracting the molar mass of Al2(SO4)3 from this gives 666 - 342 = 324 g/mol.

3. Calculate the value of x:

   • The molar mass of water (H2O) is 18 g/mol.
   • The value of x is therefore 324 / 18 = 18.

So, the value of x in the formula Al2(SO4)3•xH2O is 18.