Chem problem need help urgently

[tRNA]

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Hi,
Okay, iam trying to do this titration problem but I had no clue how to start even when I read the entire chapter about titrations in my text book, so I just looked at the answer and am still stuck on the understanding the 1st part of it, here is the problem and you may also look in your white kaplan book in ch 10 #5 Gen.Chem:

If 10 ml of 1M NaOH is titrated with 1M HCL to a pH of 2, what volume of HCL was added?

and the answer says: First we add enough HCl to neutralize the solution. since both the acid and the base are 1M, 10 ml of HCL will neutralize 10 ml of NAOH,....I got that...but then it says: This produces 20 ml of 0.5M NaCl solution....okay it produces 20ml solution, got that, but why is the concentration of NaCl 0.5M????? I thought it would be 1M since the the concentration of NaOH was 1M and the concentration on HCl was 1M too...I know that the OH will react with the H+ to produce H2O but does that affect the concentration of NaCl?? pleeeeeeease explain

don't worry about explaining the 2nd part of the problem just explain that question, I read the sect. about molarity and dilution and still didn't get it
thanks alot for your time

 

[dat_student]

Hi,
Okay, iam trying to do this titration problem but I had no clue how to start even when I read the entire chapter about titrations in my text book, so I just looked at the answer and am still stuck on the understanding the 1st part of it, here is the problem and you may also look in your white kaplan book in ch 10 #5 Gen.Chem:

If 10 ml of 1M NaOH is titrated with 1M HCL to a pH of 2, what volume of HCL was added?

and the answer says: First we add enough HCl to neutralize the solution. since both the acid and the base are 1M, 10 ml of HCL will neutralize 10 ml of NAOH,....I got that...but then it says: This produces 20 ml of 0.5M NaCl solution....okay it produces 20ml solution, got that, but why is the concentration of NaCl 0.5M????? I thought it would be 1M since the the concentration of NaOH was 1M and the concentration on HCl was 1M too...I know that the OH will react with the H+ to produce H2O but does that affect the concentration of NaCl?? pleeeeeeease explain

don't worry about explaining the 2nd part of the problem just explain that question, I read the sect. about molarity and dilution and still didn't get it
thanks alot for your time

I haven't read Kaplan's G'Chem and O'Chem sections yet. They seem boring to me. Anyhow, here is what I think:

I think you need 20.20 ml of HCl to get pH = 2

[H+] = 0.20 / 20.20 = 0.01 M
pH = -log 0.01 = 2

[Na+] = approx. 0.5 (like they said)
[Cl+] = approx. 0.5 + a little bit (you can do the math. This is because you add more HCl to get pH = 2)

[NaCl] = approx. 0.5 (seems a bit silly to even talk about [NaCl] because the two totally dissociate and [Cl] is slightly higher than [Na]

Hope that helps....

 

[captaintripps]

Hi,
Okay, iam trying to do this titration problem but I had no clue how to start even when I read the entire chapter about titrations in my text book, so I just looked at the answer and am still stuck on the understanding the 1st part of it, here is the problem and you may also look in your white kaplan book in ch 10 #5 Gen.Chem:

If 10 ml of 1M NaOH is titrated with 1M HCL to a pH of 2, what volume of HCL was added?

and the answer says: First we add enough HCl to neutralize the solution. since both the acid and the base are 1M, 10 ml of HCL will neutralize 10 ml of NAOH,....I got that...but then it says: This produces 20 ml of 0.5M NaCl solution....okay it produces 20ml solution, got that, but why is the concentration of NaCl 0.5M????? I thought it would be 1M since the the concentration of NaOH was 1M and the concentration on HCl was 1M too...I know that the OH will react with the H+ to produce H2O but does that affect the concentration of NaCl?? pleeeeeeease explain

don't worry about explaining the 2nd part of the problem just explain that question, I read the sect. about molarity and dilution and still didn't get it
thanks alot for your time

Adding 0.01L of 1mol/L Na = 0.01 moles Na (same for Cl)
Dissolving 0.01 mol NaCl in 0.02 Liters water gives 0.01/0.02=0.5 (mol/L)

 

[IcemanDDS]

so the answer is... ?

 

[dat_student]

Adding 0.01L of 1mol/L Na = 0.01 moles Na (same for Cl)
...

NOT SAME FOR Cl, you have more Cl because you must add more HCl to make the solution acidic

[Na] = approx. 0.495
[Cl] = approx. 0.505