Alkyne weighing 6.8 g completely entered into an addition reaction with 32 g of bromine.

Alkyne weighing 6.8 g completely entered into an addition reaction with 32 g of bromine. Find the molecular formula for alkyne.

First you need to write the equation for the reaction of alkyne with bromine:
CnH2n-2 + 2Br2 = CnH2n-2Br4
In our case, alkyne has multiple bonds (pi and sigma) and it attaches 4 bromine atoms.
Let’s write down the proportion to find the number of carbon and hydrogen atoms in alkyn:
6.8 – 32
14n-2 – 2 * 160

From where 14n-2 = 6.8 * 2 * 160/32 = 68
14n = 70
n = 5
This means that there are 5 carbon atoms in our alkyn.
We are looking for how many hydrogen atoms an alkyne has.
H = 2 * n – 2 = 2 * 5-2 = 8
The formula for the desired alkyne is C5H8 or pentine.