[ssethi]

Hey guys, I have three questions from my summer packet that I'm having trouble with at the moment. Don't worry, I'm not expecting answers, just guidance cause my textbook sucks. 

1. 125 mL of water is added to to 250 mL of a 1.40 M solution of ammonia. What is the molarity?

I'm confused about this one. I can't figure out how to do this. I know it seems simple, but I haven't dealt with problems where water is added to an already existent solution. I'm thinking that I have to figure out the number of moles of ammonia and then divide that by 375 mL (125 mL + 250 mL)/

2. How many mL of 0.20 M NaOH are required to neutralize 5.4 mL of 1.75 acetic acid?

I'm guessing this is a simple M1V1= M2V2 problem. Simply solve for V1.

3. 0.80 g of an unknown monoproctic acid was dissolved in 25.0 mL of water and neutralized with 52.5 mL of 0.125 M KOH. What is the molar mass of the acid?

I'm not sure how this problem is supposed to work out. I guess I'd have to figure out how much KOH was used (in moles) and then translate that into a molar mass figure for the acid. The only thing throwing off me off is the 25.0 mL of water.

Any and all help is appreciated. Thanks!

[Astrokel]

hello ssethi,

1) Yes you are correct, it is a dilution.

2) 1.75M? If so, yes you are right since it reacts in a 1:1 ratio

3) http://www.chemicalforums.com/index.php?topic=28027.0   Correct, it doesn't matter how much water you used to dissolve the acid because the mass of it is still 0.80g.

[Borek]

2. How many mL of 0.20 M NaOH are required to neutralize 5.4 mL of 1.75 acetic acid?

I'm guessing this is a simple M1V1= M2V2 problem. Simply solve for V1.

The sooner you will forgot about M1V1= M2V2 formula when it comes to stoichiometric problems, the better for you. Yes, it works. Only when you know what you are doing.

[ssethi]

Thanks for your help guys, and now I understand 2 and 3. The only thing I don't get about 1 is,when you say its a dilution, should I be doing this?

M= moles sol/ L sol
   = moles of ammonia/ .375 L

[Astrokel]

Yes you are right!