Mr$Al2(SO4)3$ Al - 26.98
S - 32.06
O - 16.00

2$Al$ + 3$S$ + 12$O$ = $2<em>26.98$ + $3</em>32.06$ + $12\ast 16$ = 213.00 g/mol

Mr$CH3COOH$ C - 12.01
H - 1.01
O - 16.00

2$C$ + 4$H$ + 2$O$ = $2<em>12.01$ + $4</em>1.01$ + $2\ast 16.00$ = 60.05 g/mol

Mr$K2Cr2O7$ K - 39.10
Cr - 52.00
O - 16.00

2$K$ + 2$Cr$ + 7$O$ = $2<em>39.10$ + $2</em>52.00$ + $7\ast 16.00$ = 294.18 g/mol

Mr$C3H5(OH)3$ C - 12.01
H - 1.01
O - 16.00

3$C$ + 8$H$ + 4$O$ = $3<em>12.01$ + $8</em>1.01$ + $4\ast 16.00$ = 89.09 g/mol