[nugiboy]

Ok im really stuck on this question:

10cm³ of a hydrocarbon, C_xH_y, were exploded with an excess of oxygen. There was a contraction in volume of 30cm³ When the products were treated with sodium hydroxide (which reacts with carbon dioxide), there was a further contraction of 30cm³. Deduce the formula of the hydrocarbon, given that all volumes were measured under the sama conditions.

Any help would be great, but a step by step answer showing working would be perfect.
Thanks in advanced!

(By the way im new here so let me know if this question would be better in a diffeerent section of the forums)

[Yggdrasil]

First, always start with a balanced chemical reaction (in terms of x and y).

Second, by Avogadro's law, the volumes of your gases will be proportional to the number of moles of each gas.  So, for example, you could restate the problem as saying:

1 mol of a hydrocarbon, CxHy, were exploded with an excess of oxygen. The total number of moles of gas went down by 3mol. When the products were treated with sodium hydroxide (which reacts with carbon dioxide), there was a a loss of 3 mol of gas. Deduce the formula of the hydrocarbon, given that all volumes were measured under the sama conditions.

You could also approach the problem by just thinking about conservation of mass (for example, the number of carbon atoms on both sides of the equation must be the same).