Find the molar mass of aluminum sulfate . Indicate the relative molecular weight of the substance.

given:
АІ2(SО4)3
find:
М[АІ2(SО4)3] -?
Мr[АІ2(SО4)3] -?
Solution:
М[АІ2(SО4)3] = А(АІ) • n(АІ)  + А(S) • n(S)  + А(О) • n(О)  
М[АІ2(SО4)3] = 27 • 2 + (32 + 16 • 4) • 2 = 54 + 96 • 3 =
=  54 + 288 = 342 g/mol
Мr[АІ2(SО4)3] = Аr(АІ) • n(АІ)  + Аr(S) • n(S)  + Аr(О) • n(О)  
Мr[АІ2(SО4)3] = 27 • 2 + (32 + 16 • 4) • 2 = 54 + 96 • 3 =
=  54 + 288 = 342 .
Answer: М[АІ2(SО4)3] = 342 g/mol;  Мr[АІ2(SО4)3] = 342.