April 19, 2024, 09:30:06 PM
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Topic: How to find the pH of 32 mL of 0.1 M of NaOH added to 100mL of 0.05 of NaHCO3  (Read 3415 times)

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Offline Tanny

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How to find the pH of 32 mL of 0.1 M of NaOH added to 100mL of 0.05 of NaHCO3
Steps please!!!
OH-    +    HCO3 - --->    CO2    - +H2O

2.4x 10^-2      3.78 x 10^-2                   0

 -x        -x                   +x

 4.68 x 10^-11 = [2.4x 10^-2-x][3.78 x 10^-2-x]/


x = 2.06 x 10^-7

There are no H3O+ or OH -, how do I find the pH???

Offline Rutherford

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A NaHCO3 and Na2CO3 buffer is made. Use the Henderson-Hasselbach equation to calculate the pH.

Offline Tanny

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OH-    +    HCO3 - --->    CO2    - +H2O

pH = pKa + log (base/acid)


What is the base? Is it just the OH or multiplied the HCO3? Since HCO3 produces a conjugate CO2- acid, is that a base too??

I made a mistake up there. The x is x = 5.95 x 10 ^-3.
Is the equation 10.329 + log ([OH-][HCO3]-/[CO2]-)? or 10.329 + log ([OH-]/[CO2]-)??
I also need help finding the buffer capacity. I never learned it but I need to do it.
I have an one hour limit.

Offline Rutherford

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NaHCO3+NaOH-->Na2CO3+H2O
Calculate the concentration of the produced Na2CO3 and the concentration of the NaHCO3 that left in the solution. Na2CO3 will ionize to 2Na+ and CO32-, and NaHCO3 will ionize to Na+ and HCO3-. HCO3- is the acid because it is a proton donor (it can donate a H+ ion) and CO3- is the base because it can only accept a proton (H+). pKa you can calculate from the Ka (pKa=-logKa).

Offline Tanny

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What about the OH on NaOH? Is that ignored? I already found their respective concentrations?

Offline Rutherford

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NaOH reacts completely with NaHCO3 to form Na2CO3.

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