text: help with chemistry? i am studying for a big final and i need help with the following problems: please help me choose the right answer --------------------------------------------- 1.which of the following would express the approximate density of carbon dioxide gas at 0°c and 2.0 atm pressure(in grams per liter)? a.) 2g/l b.) 4g/l c.) 6g/l d.) 8g/l e.) none of the above ---------------------------------------------- 2. the combustion of carbon monoxide yields carbon dioxide. the volume of oxygen gas needed to produce 22 grams of carbon dioxide at stp is a.) 4.0 liters b.) 5.6 liters c.) 11 liters d.) 22 liters e.) 32 liters --------------------------------------------------- 3. if the average velocity of a methane molecule, ch4, is 5.00x10^4 cm/sec at 0°c, what is the average velocity of helium molecules at the same temperature and pressure conditions? a.) 2.5x10^4 cm/sec b.) 5.0x10^4 cm/sec c.) 1.0x10^4 cm/sec d.) 2.0x10^4 cm/sec e.) 5.0x10^4 cm/sec 1. through some re-working of the ideal gas law, pv = nrt, you can get m = (drt)/p where m is the molecular mass, d is the density, and r is the gas constant, 0.08206. plug in your values, minding tempurature must be in k and solve for d. i got 3.9, rounding give 4 g/l or b.  ---------------  2.first you have to balance the combustion reaction co + o2 => co2. so you'd have a 1/2 in front of the o2, and that should be it. then you just convert 22 grams of co2 into moles of co2 and use the balanced reaction coefficients to see how many moles of o2 you will need (i.e. divide the number of co2 moles by 2 to get o2 moles) thenjust plug everything into pv = nrt again and solve for v. i got 5.6 l or b.  ---------------  3. although there are alot of ways to do this, the way i do it is like this. r1/r2 = sqrt(m2/m1) where r is the speed of each molecule in question and m is the molecular mass. notice how the order changes on each side of the equation - this is not a mistake. so you just plug everything in and solve for r2 (or r1 depending on how you set it up). i got 2.5 e 4 or a. also, just in case, sqrt means square root.