Question

I am planning to make a dilution of Co2 into several concentrations (400ppm to 1000ppm) from purified air cylinder and purified carbon dioxide cylinder in a 2L dilute flask.

My idea is using the ideal gas law, PV=nRT, so since R and T is constant, I am having problems to get the value of P from the CO2 and the air.

Does the P value comes from the pressure of gas in the cylinder or, should I set the P to certain value?

Also, for the purified air it is made of 21% oxygen and 79% nitrogen, I am confused to how to calculate the num of mole.

Thank you.