Calculate the pH of Buffer Solution with Ka=1.34x10^-5

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In summary, a buffer solution is prepared by mixing 380.0 ml of 0.250 M propionic acid, C2H5COOH, and 120.0 ml of 0.350 M sodium propionate, C2H5COONa, with a Ka value of 1.34 X 10^-5. The initial molarities of C2H5COOH and C2H5COO- are 0.19 M and 0.084 M, respectively. Using the x-method, the pH of the buffer solution is determined to be 3.002.
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lizzyb
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A buffer solution is prepared by mixing 380.0 ml of 0.250 M propionic acid, C2H5COOH, and 120.0 ml of 0.350 M sodium propionate, C2H5COONa. Calculate the pH of the prepared buffer solution. For propionic acid, Ka = 1.34 X 10^-5.

Work thus far

Code:
  We have this

  C2H5COOH <--> C2H5COO- + H+

  Since the C2H5COONa goes to completion and is left
  with C2H5COO-, we can determine the initial amount
  of C2H5COO-, and then we use the x-method to determine
  the pH.

  Initial Molarities:

                 .250 M .380 L     .250 * .380
   [C2H5COOH] = --------------- = ------------ = .19 M
                 (.380 + .120)L        .5      


                 .350 M * .12 L     .350 * .12
   [C2H5COO-] = ---------------- = ------------ = .084 M
                 (.380 + .120) L      .5

  C2H5COOH   <-->     C2H5COO-    +        H+

    .19                 .084               0       initial
     -x                  x                 x       change
   .19-x               .084+x              x       equilibrium

  so,

                         (.084 + x) x
     Ka = 1.34 X 10^-5 = --------------
                          (.19-x)

     ==> x = 3.029 X 10^-5, pH = -log(x) = 3.002

does this look okay to you?
 
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  • #2
Yes. ... ..
 
  • #3
thank you! :-)
 

1. What is a buffer solution?

A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added to it. It is made up of a weak acid and its conjugate base (or a weak base and its conjugate acid) and helps maintain a stable pH in a system.

2. How do you calculate the pH of a buffer solution?

The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where pKa is the dissociation constant of the weak acid, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid.

3. What is Ka in the Henderson-Hasselbalch equation?

Ka is the dissociation constant of the weak acid in the buffer solution. It is a measure of the strength of the acid and its tendency to dissociate in water. The lower the Ka value, the weaker the acid.

4. How does Ka affect the pH of a buffer solution?

The Ka value directly affects the pH of a buffer solution. A lower Ka value means a weaker acid and a higher pH, while a higher Ka value means a stronger acid and a lower pH. In the Henderson-Hasselbalch equation, a lower Ka value will result in a higher pH and a higher Ka value will result in a lower pH.

5. Can you explain the significance of Ka=1.34x10^-5 in the Henderson-Hasselbalch equation?

The Ka=1.34x10^-5 in the Henderson-Hasselbalch equation represents the dissociation constant of the weak acid in the buffer solution. This value is used to determine the strength of the acid and its impact on the pH of the buffer solution. In this case, a lower Ka value indicates a weaker acid and a higher pH, while a higher Ka value indicates a stronger acid and a lower pH.

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