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| Eoghan... |
 Posted: Thu Jun 19, 2008 1:42 am |
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Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer. |
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| Bill Penrose... |
| Posted: Thu Jun 19, 2008 2:20 am |
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On Jun 19, 3:42 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Quote: Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
Check your textbook. It's all in there.
Take heart. Everyone has trouble with buffer questions at first.
DB |
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| Eoghan... |
| Posted: Thu Jun 19, 2008 2:59 am |
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Quote: Check your textbook. It's all in there.
Take heart. Everyone has trouble with buffer questions at first.
DB
I've checked it but I could't find the soultion.
I know that I need H2O and CH3CO2H and that the concentration of
CH3CO2H must be equal to the concentration of CH3CO2-, but I can't
determine the volumes |
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| Eoghan... |
| Posted: Thu Jun 19, 2008 3:06 am |
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On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Quote: Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M |
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| Eoghan... |
| Posted: Thu Jun 19, 2008 3:30 am |
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On Jun 19, 3:06 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Quote: On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M
I have tried to do the following:
I take 0.1L of CH3COOH 3M so I have 0.3mol
Now I have this reaction: CH3CO2H + OH- (from NaOH) ------> CH3COOH +
H2O
I have to get the some number of moles of CH3COOH and of CH3COO-
so I need 1.5mol of OH-
OH- is 2.00M so I have to take 0.75L of NaOH
So I take 0.1L of CH3COOH and 0.75L of NaOH i.e. 0.85L of solution
In order to have 1.70L I add to the solution 0.85L of H2O
The problem is: how can I have a concentration of 0.07M? |
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| Eoghan... |
| Posted: Thu Jun 19, 2008 7:40 am |
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On Jun 19, 6:37 pm, Marvin <physc... at (no spam) verizon.net> wrote:
Quote: Eoghan wrote:
Check your textbook. It's all in there.
Take heart. Everyone has trouble with buffer questions at first.
DB
I've checked it but I could't find the soultion.
I know that I need H2O and CH3CO2H and that the concentration of
CH3CO2H must be equal to the concentration of CH3CO2-, but I can't
determine the volumes
If so, you haven't learned what you should have by this late
in the course. Things like molar concentrations, molecular
weight, etc.
I know theory but i can't put it into practice. I know what molar
oncentration and molar weight are... but still I need an help to solve
this problem... please help |
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| Marvin... |
| Posted: Thu Jun 19, 2008 11:37 am |
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Eoghan wrote:
Quote: Check your textbook. It's all in there.
Take heart. Everyone has trouble with buffer questions at first.
DB
I've checked it but I could't find the soultion.
I know that I need H2O and CH3CO2H and that the concentration of
CH3CO2H must be equal to the concentration of CH3CO2-, but I can't
determine the volumes
If so, you haven't learned what you should have by this late
in the course. Things like molar concentrations, molecular
weight, etc. |
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| ... |
| Posted: Thu Jun 19, 2008 12:44 pm |
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On Jun 19, 6:06 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Quote: On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M
That's a strange requirement.
Do you mean [H3O+] must be 0.07M? pH = - log_10(0.07M)?
Or that the total concentration of all cations and anions must be
0.07M?
Typically you have a target pH in mind when you prepare a buffer
solution
Michael |
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| Bob... |
| Posted: Thu Jun 19, 2008 9:41 pm |
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On Thu, 19 Jun 2008 04:42:27 -0700 (PDT), Eoghan <lucagalbu at (no spam) gmail.com>
wrote:
Quote: Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
One reason you are having trouble is that the question is not well
defined.
Later you added
Quote: I've missed to say that the buffer solution must be 0.07M
Even with that, it still is not clear what the goal is.
Usually we would describe a buffer by its constituents, its
concentration, and its pH.
It is not clear what the 0.07 M refers to. Perhaps the concentration,
but someone else thought it was the pH (the H+).
One could make many different buffers from the ingredients you list.
The problem is that, for some reason, you have given us an incomplete
statement of a problem. I suspect you have not quoted it to us
completely. If it is complete, you need to go back to your instructor
and clarify.
If you can figure out what the Q is, it probably involves dilution and
simple application of Henderson-Hasselbalch.
bob |
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| Eoghan... |
| Posted: Thu Jun 19, 2008 11:22 pm |
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On Jun 20, 12:44 am, mrdarr... at (no spam) gmail.com wrote:
Quote: On Jun 19, 6:06 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M
That's a strange requirement.
Do you mean [H3O+] must be 0.07M? pH = - log_10(0.07M)?
Or that the total concentration of all cations and anions must be
0.07M?
Typically you have a target pH in mind when you prepare a buffer
solution
Michael
I think that it is the total concentration of all cations and anions |
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| ... |
| Posted: Fri Jun 20, 2008 6:32 am |
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On Jun 20, 2:22 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Quote: On Jun 20, 12:44 am, mrdarr... at (no spam) gmail.com wrote:
On Jun 19, 6:06 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M
That's a strange requirement.
Do you mean [H3O+] must be 0.07M? pH = - log_10(0.07M)?
Or that the total concentration of all cations and anions must be
0.07M?
Typically you have a target pH in mind when you prepare a buffer
solution
Michael
I think that it is the total concentration of all cations and anions
Well ask him.
You'll probably get extra credit in his eyes if you ask him, "Do you
mean the osmolarity is 0.07M?"
Michael |
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| Lloyd... |
| Posted: Fri Jun 20, 2008 8:34 am |
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On Jun 19, 9:30 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Quote: On Jun 19, 3:06 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M
I have tried to do the following:
I take 0.1L of CH3COOH 3M so I have 0.3mol
Now I have this reaction: CH3CO2H + OH- (from NaOH) ------> CH3COOH +
H2O
I have to get the some number of moles of CH3COOH and of CH3COO-
so I need 1.5mol of OH-
OH- is 2.00M so I have to take 0.75L of NaOH
So I take 0.1L of CH3COOH and 0.75L of NaOH i.e. 0.85L of solution
In order to have 1.70L I add to the solution 0.85L of H2O
The problem is: how can I have a concentration of 0.07M?
What pH do you need? If acidic, you'll make if from HOAc and OAc-,
adding NaOH to the HOAc to convert some of it into OAc-. To find how
much, use the relation:
Ka = [H+] x (moles OAc-) / (moles HOAc)
For every mole of NaOH you add, you make one mole of OAc- and use up 1
mole of HOAc. So set up an algebraic relationship.
It's like the calculation you do to find the pH in the titration of
HOAc with NaOH.
If you need a basic pH, you'd make it from NH3 and NH(4)+. You'd add
HCl to your NH3 to convert some of it to NH(4)+. |
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| poindexter... |
| Posted: Mon Jun 23, 2008 4:23 am |
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On Jun 19, 6:30 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Quote: On Jun 19, 3:06 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M
I have tried to do the following:
I take 0.1L of CH3COOH 3M so I have 0.3mol
Now I have this reaction: CH3CO2H + OH- (from NaOH) ------> CH3COOH +
H2O
I have to get the some number of moles of CH3COOH and of CH3COO-
so I need 1.5mol of OH-
OH- is 2.00M so I have to take 0.75L of NaOH
So I take 0.1L of CH3COOH and 0.75L of NaOH i.e. 0.85L of solution
In order to have 1.70L I add to the solution 0.85L of H2O
The problem is: how can I have a concentration of 0.07M?
H-H equation will give you the ratio [A-]/[HA] required; that's one
equation. To solve it, you need another equation relating the two
unknowns. That equation is [A-] + [HA] = 0.07.
Set up and solve those equations. The rest of the questionis a
stoichiometry problem inserted to confuse the student. |
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| poindexter... |
| Posted: Mon Jun 23, 2008 5:08 am |
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On Jun 23, 7:23 am, poindexter <gmilli... at (no spam) stmartin.edu> wrote:
Quote: On Jun 19, 6:30 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
On Jun 19, 3:06 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M
I have tried to do the following:
I take 0.1L of CH3COOH 3M so I have 0.3mol
Now I have this reaction: CH3CO2H + OH- (from NaOH) ------> CH3COOH +
H2O
I have to get the some number of moles of CH3COOH and of CH3COO-
so I need 1.5mol of OH-
OH- is 2.00M so I have to take 0.75L of NaOH
So I take 0.1L of CH3COOH and 0.75L of NaOH i.e. 0.85L of solution
In order to have 1.70L I add to the solution 0.85L of H2O
The problem is: how can I have a concentration of 0.07M?
H-H equation will give you the ratio [A-]/[HA] required; that's one
equation. To solve it, you need another equation relating the two
unknowns. That equation is [A-] + [HA] = 0.07.
Set up and solve those equations. The rest of the questionis a
stoichiometry problem inserted to confuse the student.
Oops...second equation should be [A-] + [H3O+] = 0.07. |
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| Lloyd... |
| Posted: Mon Jun 23, 2008 9:06 am |
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Guest
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On Jun 19, 9:06 am, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Quote: On Jun 19, 1:42 pm, Eoghan <lucaga... at (no spam) gmail.com> wrote:
Hi there.. can you please help me with this problem?
I have to prepare 1.70L of a buffer solution. I have these reactants:
deionized water; HCl 1.00M; NaOH 2.00M; NH3 2.50M; CH3CO2H 3.00M. I
have to calculate the volumes of the reactants needed for the buffer.
I've missed to say that the buffer solution must be 0.07M
In what? The conjugate acid? The conj base? The two put together? |
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