Chem II questions...

[arcenite]

Hello fellow ATOTers, I'm having trouble with a few problems that are really racking my brain... I should know this stuff, but for some reason I can't get it together...

1.) An aqueous solution is 34% H(sub 3)PO(sub 4) by mass and has a density of 1.209g/mL. What are the molarity and molality.

I know that molarity is moles/kg.. but I have no idea how to pull moles or mass out of that question.

2.) Calculate the mole fraction of solute in the following aqueous solutions: a.) 21.7% C(sub 2)H(sub 5)OH b.) 0.684m (molality) CO(NH(sub 2))

Again, I understand how Mole Fractions work, I just have no idea how to pull the moles out of that equation.

3.) You are asked to prepare 125.0mL of 0.0321 M AgNO(sub 3). How many grams would you need of a sample known to be 99.81% by mass?

This one is really racking my brain, it's almost like I know exactly how to do it, but i'm missing something.

Any help would be greatly appreciated 🙂

Thanks.
Bill

 

[jkj]

I dont want to do the problem for you, but maybe this will get you started. Assume 1 L of solution. From the density you gave that ill give you how many grams of actual h3po4 you have.

 

[jkj]

Let me know if you need some more help