Question

Can anyone help me on this question? I really need help plz.
A student combusts 3.15 g of a simple hydrocarbon and collects the carbon dioxide gas produced in a GIGANTIC graduated cylinder inverted in water. The volume of gas collected is 4.79 L, the pressure in the room is 781 mm Hg, and the temperature in the room and the water is 29.3'C. What is the vapor pressure of water at this temperature?

Answer 1

Well, when you see combustion of a hydrocarbon (in general, combustion), that should tell you that you have two products: CO\(_2\) gas and water vapors.
Also, notice what you're given here, n, V, and T.
Which means, you can also use the ideal gas law formula. (if you look in your book for mor information, you can also solve this using the clausias clapeyron equation).

The vapor pressure of a liquid does not depend on the amount on the liquid in the container, be it one liter or thirty liters; at the same temperature, both samples will have the same vapor pressure. So, if you can solve for one, you can solve for the other.

Solve and rearrange for what you need.