Question

AL2(SO4)3.XH2O has 8.1% aluminium by mass.The value of X ?

Answer 1

The general formula is Al2(SO4)3 × xH2O. You can set up the equation for mass percentage as w(Al) = 2M(Al) / [M(Al2(SO4)3) + x×M(H2O)] = 0.081, and then solve for x.

The M are molar masses which can be calculated by adding the relative atomic masses from the periodic system.

I won't tell you the result now, but you can let us know what you got.

Answer 2

Answer:

The value of X is 18.

Explanation:

Molar mass of the $AL_2(SO_4)_3.XH_2O$ = M

Percentage of aluminum in $AL_2(SO_4)_3.XH_2O$ = 8.1 %

Percentage of an element in a compound:

$\frac{\text{Number of atoms of element}\times \text{Atomic mass of element}}{\text{molecular mass of element}}\times 100$

$8.1\%=\frac{2\times 27 g/mol}{M}\times 100$

M = 666.66 g/mol

Molar mass of the $AL_2(SO_4)_3.XH_2O$ = M =666.66 g/mol

$2\times 27 g/mol+3\times 32 g/mol+12\times 16 g/mol+X\times 18 g/mol=666.66 g/mol$

X = 18.03 ≈ 18

The value of X is 18.