Question

What is the significance of collecting a gas over water (what does this mean and how does it impact your calculations)?

Answer 1

Mostly the amount of gas given off by the reaction. and the gases are small density. we do not collect gases an find the mass of gas. and we can say that gases are not particularly soluble in water. it is able to be collect the evolved gas by displacement of water from a container.when we arrange for the collection of a gas over water than a container in which the reaction takes place and a gas collection container filled with water and inverted in a reservoir of water.   when we attaching hose at one end then and the gas collected into the container and inserting the other up into the inverted gas collection bottle. gas is created and displace water from the bottle. And the volume of gas can be determined by the amount of water that was displaced by the gas.

Dalton's Law of Partial Pressures stated that the total pressure in the container must be the sum of the pressures of the gas we collected and the water vapour.

P_T= P_gas+ P_H2O

we want to calculate the pressure of collected gas then follow these equations-

                                     PV=nRT

This equation is called the ideal gas law.

p= pressure of gas

v= volume of water displaced

n= no. of moles

R= ideal gas constant

T= temperature of gas