Question

Why is carbondioxide cooled to room temperature before it's passed through potassium hydroxide solution

Answer 1

Answer:

The important thing to realize here is that all volumes were measured under the same conditions for pressure and temperature.

This means that the volume ratios that exists between the gaseous compounds is equivalent to the mole ratios that exist between the same species.

It's important to set up a generic balanced chemical equation for the combustion of your hydrocarbon, which we'll name CxHy,

CxHy+O2(g]→CO2(g]+H2O(l]

Balance this by using x and y. Since x moles of carbon are present on the reactants' side, you need x present on the products' side as well.

CxHy+O2(g]→xCO2(g]+H2O(l]

You have y moles of hydrogen on the reactants' side, and 2 on the products' side, so multiply the water by y2

CxHy+O2(g]→xCO2(g]+y2H2O(l]

FInally, the number of moles of oxygen will be

CxHy+(2x+y2)O2(g]→xCO2(g]+y2H2O(l]

Now, another important thing to realize here is that oxygen is present in excess. Notice that the reaction produces carbon dioxide, a gas, and liquid water.

This means that the remaining 1000 cm3 of gas will represent a mixture of excess oxygen and carbon dioxide. Here is where the sodium hydroxide solution comes into play.

Sodium hydroxide solutions will absorb carbon dioxide to form potassium carbonate, K2CO3, and water.