# topscore help

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#### MoThuggy

##### Member
10+ Year Member
15+ Year Member

I had two questions that i couldnt figure out in the second topscore exam, i would appreciate the help (i woudl appreciate it if someone could walk me through the second problem):

1) if you have a solution of 1L H2O and 234 grams of NaCl, what is the osmotic pessure at STP (R=.1L*atm/mol*K)? {if i use the formula os pressure= mRT then i keep on getting 109.2 atm but the correct answer is 218.4 atm

2) What volume of HCl was added if 20 mL of 1M NaOH is titrated with 1 M HCl to produce a pH=2?

thanks guys.

#### luder98

##### Senior Member
10+ Year Member
5+ Year Member
MoThuggy said:
I had two questions that i couldnt figure out in the second topscore exam, i would appreciate the help (i woudl appreciate it if someone could walk me through the second problem):

1) if you have a solution of 1L H2O and 234 grams of NaCl, what is the osmotic pessure at STP (R=.1L*atm/mol*K)? {if i use the formula os pressure= mRT then i keep on getting 109.2 atm but the correct answer is 218.4 atm

2) What volume of HCl was added if 20 mL of 1M NaOH is titrated with 1 M HCl to produce a pH=2?

thanks guys.
Both of these were asked before. You should be able to find them under those gen chem question threads for more details.

1) NaCl dissociates into two ions, Na+ and Cl-. So you need to multiply M (not m as shown in your formula) by 2.

2) Let x ml be the needed HCl. Just set up the problem as you normally do. One thing to remember is that since pH is 2, NaOH will be used up and HCl will be leftover after the rxn.