To calculate the molar mass of a compound, we need to find at the periodic table the atomic mass of each element that belongs to the compound and then we multiply for the quantity of atoms of it.
So, for:
5. K2Cr2O7:
K = 39 g/mol
Cr = 52 g/mol
O = 16 g/mol
(2x39) + (2x52) + (7x16) = 78 + 104 + 112 = 294 g/mol
Molar mass of K2Cr2O7 = 294 g/mol
6. C12H22O11
C = 12 g/mol
H = 1 g/mol
O = 16 g/mol
(12x12) + (22x1) + (11x16) = 144 + 22 + 176 = 342 g/mol
Molar mass of C12H22O11 = 342 g/mol