Chem help! Please!?

Question

I have two chem problems that I just cannot figure out. They are on Ideal Gas Law problems.
Please provide with me work (so i can see how to do it) and an answer.

1) 4.5g of magnesium is reacted with hydrochloric acid to produce hydrogen gas and a solution of magnesium chloride. What volume of gas would be produced at 2.5 atm and -8 degrees Celsius? PH20=2.5 mm Hg at -8 degrees Celsius

2) The density of a gas at room temperature (21 degrees Celcius) is 2.44 g/L. If the pressure of the gas is 0.178 atm what is the MM of the gas? (HINT: Does the density of a gas change based on the size of the sample?)


THANK YOU SOOO MUCH!

I figured out the 1st one. Thanks for all of your help. I did the 2nd one and got 331.072 g/mol. I would really appreciate it, if someone would do the problem, and let me know if you got the same answer as me. If not, it would be so great if you could explain how you got your answer.
Thanks again!

Answer 1

Mg + 2HCl ===> MgCl2 + H2 Atomic weights: Mg = 24

4.5gMg x 1molMg/24gMg x 1molH2/1molMg x 22.4LH2/1molH2 x 1atm/2.5atm x 265K/273K = (4.5)(22.4)(265)/(24)(2.5)(273) = 1.63L H2

The 4.5g Mg is given. The first factor comes from the atomic weight. The g Mg cancel, leaving moles (gram atoms) Mg. The second factor comes from the balanced equation. The moles Mg cancel leaving moles H2. The third factor comes from the molar volume of a perfect gas. The moles H2 cancel, leaving L H2. The fourth factor comes from the need to make the volume smaller, because the pressure is greater than 1 atm, so multiply by anumber less than 1. The fifth factor comes from the need to make the volume still smaller, because the temp is less than 273K, by multiplying by another number less than 1.

Answer 2

I won't give you the exact answers, but i'll try to help you get started....

1) Write out the balanced chemical reaction. Determine how many moles of H2 will be formed based on the stochiometry and the fact that you start with 4.5 g Mg. Take the moles you calculated and plug it into PV=nRT along with the given information. (rember R is a constant, but use the right units!)