A gas cylinder contains 2.0 mol of gas X and 6.0 mol of gas Y at a total pressure of 2.1 atm. What is the partial pressure of gas Y?

The answer is 1.6 atm. Let's first calculate the mole fraction of gas Y. The mole fraction (x) is: x = n1/n, where n1 is a number of moles of an individual gas in a mixture and n is total moles of the gas mixture. We know that n1 of gas Y is 6.0 mol (n1 = 6.0 mol) and that there are in total 8. mol of the gas mixture (n = 2.0 + 6.0 = 8.0 mol). Now calculate the mole fraction of gas Y. x = 6.0/8.0 = 0.75. Now, let's use the mole fraction of gas Y (x) and the total pressure (P) to calculate the partial pressure of gas Y (P1) : x = P1/P. P1 = x * P. If x = 0.75 and P = 2.1 atm, then the partial pressure of gas Y is: P1 = 0.75 * 2.1 atm = 1.6 atm.