Question

10 ml of gaseous hydrocarbon was exploded with
an excess of oxygen. The observed contraction was
25 ml, and on treatment with KOH there was a
further contraction of 20 ml. What is the molecular
formula of hydrocarbon ?
​

Answer 1

Answer:

The initial volume of hydrocarbon = 10 ml

After the observed contraction, the volume remains = 25 ml

On treating with KOH, the volume further reduces to = 20 ml

Let the molecular formula of the gaseous hydrocarbon be “CxHy”, where “x” is the no. of carbon atoms and “y” is the no. of hydrogen atoms present in the hydrocarbon.

Let’s write a balanced equation according to the reaction process given in the question,

CxHy (g) + (x+y/4) O₂ (g) → x CO₂ (g) + (y/2) H₂O(l)

Since after treating with KOH, the CO₂ will be absorbed, therefore, we can write

10 x = 20

Or, x = 2 ….. (i)

Now, let’s say that, before the first contraction and the second contraction on treating with KOH, the volume was (25 + 20) ml = 45 ml.  

Therefore, in order to find the value of y, we can write an equation based on the balanced equation as above as,

10 + 10(x+y/4) = 25 + 20

⇒ 10 + 10(2 + y/4) = 45 …. [from (i)]

⇒ 1 + 2 + y/4 = 45/10

⇒ y/4 = (45-30)/10

⇒ y = (4 * 15) / 10

⇒ y = 6 ..... (iii)

from (i) & (iii), we get

CxHy = C₂H₆

Thus, the molecular formula of the hydrocarbon is C₂H₆.

Answer 2

Answer:

The underlying volume of hydrocarbon = 10 ml  

After the watched constriction, the volume remains = 25 ml  

On treating with KOH, the volume further decreases to = 20 ml  

Give the atomic equation of the vaporous hydrocarbon a chance to be "CxHy", where "x" is the no. of carbon molecules and "y" is the no. of hydrogen molecules present in the hydrocarbon.  

How about we compose a decent condition as per the response procedure given in the inquiry,  

CxHy (g) + (x+y/4) O₂ (g) → x CO₂ (g) + (y/2) H₂O(l)  

Since subsequent to treating with KOH, the CO₂ will be assimilated, in this way, we can compose

10 x = 20  

Or then again, x = 2 … .. (I)  

Presently, suppose that, before the primary compression and the subsequent constriction on treating with KOH, the volume was (25 + 20) ml = 45 ml.  

Consequently, so as to discover the estimation of y, we can compose a condition dependent on the reasonable condition as above as,

10 + 10(x+y/4) = 25 + 20  

⇒ 10 + 10(2 + y/4) = 45 … . [from (i)]  

⇒ 1 + 2 + y/4 = 45/10  

⇒ y/4 = (45-30)/10  

⇒ y = (4 * 15)/10  

⇒ y = 6  

..... (iii)  

from (I) and (iii), we get  

CxHy = C₂H₆  

Consequently, the sub-atomic recipe of the hydrocarbon is C₂H₆.