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An analytical chemist is titrating 132.3 mL of a 0.7100 M solution of methylamine (CH,NH2 with a 0.7500 M solution of HNO 3* The p K, of methylamine is 3.36. Calculate the pH of the base solution after the chemist has added 111.4 mL of the HNO3 solution to it. Note for advanced students: you may assume the final volume equals the initial volume of the solution plus the volume of HNO3 solution added Round your answer to 2 decimal places.

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Explanation:

Calculate the moles of [tex]CH_{3}NH_{2}[/tex] as follows.

                    = 0.1323 L x 0.7100 M

                    = 0.0940 mol

Now, calculate the moles of [tex]HNO_{3}[/tex] as follows.

                   = 0.1114 L x 0.7500 M

                   = 0.0836 mol

According to the ICF table,

      [tex]CH_{3}NH_{2} + H^{+} \rightarrow CH_{3}NH_{3}^{+}[/tex]  

Initial :    0.0940 mol       0.0836mol              0.0 mol

Change: -0.0836            -0.0836                    +0.0836

Final:    0.0104 mol          0.0 mol                   0.0836 mol

According to Henderson-Hasselbalch equation, we have

          [tex]pOH = pK_{b} + log \frac{[CH_{3}NH_{3}^{+}]}{[CH_{3}NH_{2}]}[/tex]

Putting the given values into the above equation we get the value of pOH as follows.

       [tex]pOH = pK_{b} + log \frac{[CH_{3}NH_{3}^{+}]}{[CH_{3}NH_{2}]}[/tex]      

                pOH = 3.36 + log [tex]\frac{0.0836}{0.0104}[/tex]

                          = 3.36 + 0.905

                         = 4.265

Therefore, calculate the pH as follows.

                    pH = 14 - 4.265

                           = 9.7

Thus, we can conclude that the pH of the given base solution is 9.7.

The pH of the base solution after the chemist has added 111.4 mL of the HNO3 solution is mathematically given as

pH= 9.7

What is the pH of the base solution after the chemist has added 111.4 mL of the HNO3 solution to it.?

Question Parameter(s):

An analytical chemist is titrating 132.3 mL of a 0.7100 M solution

The p K, of methylamine is 3.36.

Generally, the equation for the Chemical Reaction  is mathematically given as

CH3NH2 + H^{+}----> CH_{3}NH3^{+}  

Therefore

[tex]pOH = pK_{b} + log \frac{[CH_{3}NH_{3}^{+}]}{[CH_{3}NH_{2}]}[/tex]

[tex]pOH = 3.36 + log \frac{0.0836}{0.0104}[/tex]

pOH= 4.265

In conclusion, The pH is

pH = 14 - 4.265

pH= 9.7

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