TopScore 2 - GC #68 - Help

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

I hate TopScore's super dry useless explanations...can someone please help
 
Given:
pH = 2
[H+] = 10^(-2)
[H+] = 0.01 M

-> This is where the 0.01 M came from

Since HCl + NaOH -> H2O + NaCl, it's a neutralization reaction.

20 mL 1M HCl + 20 mL 1M NaOH = 40 mL of water

If we keep adding HCl, the pH goes down as HCl will dissociate into H+ and Cl-.

How much extra HCl do we add?
Given:
Volume ~ 40 mL
Concentration = 0.01 M
moles = ?

c = moles/volume
moles = (0.040L)(0.01M)
moles = 0.0004 mol

We know the concentration of HCl is 1M.
So the amount of 1M HCl needed to add to the solution is..

c=moles/volume
volume = moles/concentration
volume = 0.0004 mol/1.0M
volume = 0.0004 L = 0.4 mL


Total Volume of HCl added = neutralizing volume + volume needed to lower pH
= 20 mL + 0.4 mL
= 20.4 mL

Hope this helps...
 
What volume of HCL was added if 20 mL of 1M NaOH is titrated with 1M HCl to produce a pH = 2?

I hate TopScore's super dry useless explanations...can someone please help

Not sure if I did it correctly... Is the answer 20.4 mL?


*Oops. Did not see the post before mine. Thanks Albino!
 
Given:
pH = 2
[H+] = 10^(-2)
[H+] = 0.01 M

-> This is where the 0.01 M came from

Since HCl + NaOH -> H2O + NaCl, it's a neutralization reaction.

20 mL 1M HCl + 20 mL 1M NaOH = 40 mL of water

If we keep adding HCl, the pH goes down as HCl will dissociate into H+ and Cl-.

How much extra HCl do we add?
Given:
Volume ~ 40 mL
Concentration = 0.01 M
moles = ?

c = moles/volume
moles = (0.040L)(0.01M)
moles = 0.0004 mol

We know the concentration of HCl is 1M.
So the amount of 1M HCl needed to add to the solution is..

c=moles/volume
volume = moles/concentration
volume = 0.0004 mol/1.0M
volume = 0.0004 L = 0.4 mL


Total Volume of HCl added = neutralizing volume + volume needed to lower pH
= 20 mL + 0.4 mL
= 20.4 mL

Hope this helps...

wow thanks for breaking that down for me..i still dont think i would have realized the necessary steps for all that so im going to have to go over this one a couple times...is this likely to NOT land? it seems like a lot of time/work for one problem and ive heard there isnt really that much drawn out calculation on the GC DAT?
 
Top score gotta stop with this crazy calculation problem
I heard most of the dat calculation is set up for u.
 
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