Question

a hydrocarbon is burnt in 175cm3 of oxygen. The mixture is cooled. The volume of the remaining gasses is 125cm3. The carbon is removed. This leaves 25cm3 of unreacted oxygen.
*Determine the volume of oxygen used
* Determine the volume of carbon dioxide formed
*Deduce a possible formula for the hydrocarbon
* Write a balanced equation for the reaction of this hydrocarbon with oxygen

Answer 1

a hydrocarbon is burnt in 175cm3 of oxygen. The mixture is cooled. The volume of the remaining gasses is 125cm3. The carbon is removed. This leaves 25cm3 of unreacted oxygen.

* Determine the volume of oxygen used

* Determine the volume of carbon dioxide formed

* Deduce a possible formula for the hydrocarbon

* Write a balanced equation for the reaction of this hydrocarbon with oxygen

Solution

1) The volume of oxygen used is 175 - 25 = 150 cm3

2) The volume of carbon dioxide formed is 125 - 25 = 100 cm3

3) A possible formula for the hydrocarbon is $C_nH_{2n}$ (so it is alkene or cycloalkane)

$$\begin{array}{c c} 0, 1 5 & 0, 1 \\ C _ {x} H _ {y} + (x + y / 4) O _ {2} & = x C O _ {2} + y / 2 H _ {2} O \\ 2 2, 4 (x + y / 4) & 2 2, 4 x \end{array}$$ $$\begin{array}{l} 2 2, 4 * 0. 1 5 * x = 2 2, 4 * (x + y / 4) * 0, 1 \\ 0. 1 5 x = 0, 1 x + 0, 0 2 5 y \\ 0. 0 5 x = 0. 0 2 5 y \\ y = 2 x \end{array}$$

4) $\mathrm{C_nH_{2n} + 1,5nO_2 = nCO_2 + nH_2O}$

For example $\mathrm{C}_2\mathrm{H}_4 + 3\mathrm{O}_2 = 2\mathrm{CO}_2 + 2\mathrm{H}_2\mathrm{O}$

Answer: b) decreases as the reaction proceeds.