contoh soal: tentukan massa molekul relative (mr) cuso4 jika diketahui  ar  o = 16; s = 32; cu = 63,5.
penyelesaian:  
mr cuso4        = 1(ar cu) + 1 (ar s) + 4 (ar o)  
= 1(63,5) + 1 (32) + 4 (16)  
= 159,5
penyelesaian:  
mr cuso4        = 1(ar cu) + 1 (ar s) + 4 (ar o)  
= 1(63,5) + 1 (32) + 4 (16)  
= 159,5