a) mCa(OH)2=40u+2*16u+2*1u=74 u
b) mNa2CO3=2*23u+12u+3*16u=106 u
c) mAl2(SO4)3=2*27u+3*32u+12*16u=342 u
d) m 3 Na2O=3*(2*23u+16u)=186 u
e) m 2 Cr(OH)3=2*(52u+3*16u+3*1u)=206 u
