Saturated vs Unsaturated CompoundsFrom the alkanes and alkenes chapter, we learn that alkanes have only single bonds and are saturated compounds. On the other hand, alkenes have double bonds, and are unsaturated compounds. A common test for saturation (or to distinguish alkanes from alkenes) is to add aqueous bromine (in the dark). Alkenes will turn reddish brown bromine colorless. For alkanes, bromine will remain reddish brown.
This video from youtube is a good illustration of the test:
Formula of Alkane and AlkeneIn O Levels, they generally tell you that alkane has a general molecular formula of CnH2n+2, while alkene has a general molecular formula of CnH2n. Note that the alkene general molecular formula of CnH2n only applies to straight chain alkene with just one double bond. What happens when there is more than one double bond?
Every additional double bond you have will decrease the number of hydrogen atoms by 2.
Number of double bonds = (42 - 30)/2 = 6
One mole of double bond will react with one mole of bromine. With 6 double bonds, it means 6 moles of bromine.