Mr ( Ca ) = 40 w ( Ca ) = 100 * 0,4 = 40 % Mr ( C ) = 12 w ( C ) = 100 * 0,12 = 12 % Mr ( O ) = 16 * 3 ( 3 атома ) w ( O ) = 100 * 0,48 = 48 % Mr ( H2CO3 ) = 100