Problem: Calculate the pH after 0.020 mole of NaOH is added to 1.00 L of each of the following solutions:a. pure H2Ob. a mixture containing 0.100 M HC3H5O2 and 0.100 M NaC3H5O2

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We are asked to calculate the pH after 0.020 mole of NaOH is added to 1.00 L of each of the following solutions


a. pure H2O

pH will depend on NaOH  (strong base) 

Calculate pOH: 

pOH = -log[OH-]pOH = -log[0.020]

pOH = 1.70


Calculate pH : 

pH= 14 - pOHpH= 14 - 1.70

pH = 12.30


The resulting solution after the titration has a pH of 12.30.


b. a mixture containing 0.100 M HC3H5O2 and 0.100 M NaC3H5O2


Step 1. Calculate the initial amounts of HC3H5O2 in moles before the reaction happens.

molarity (volume) → moles

Recall:

*convert volumes from mL to L → 1 mL = 10-3 L


  1.00 L of 0.100 M HC3H5O2

 mol HC3H5O2= 0.100 mol HC3H5O21 L×1 L

mol HClO = 0.100 mol HClO


  1.00 L of 0.100 M  NaC3H5O2

 mol NaC3H5O2= 0.100 mol NaC3H5O21 L×1 L

mol  NaC3H5O2 = 0.100 mol  NaC3H5O2


Step 2. Write the chemical equation for the reaction between HC3H5O2 and NaOH.

Reaction:

HC3H5O2(aq)    +   NaOH(aq)               C3H5O2(aq)       +       H2O(aq) 
 (weak acid)          (base)                    (conjugate base)     (conjugate acid)


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Problem Details

Calculate the pH after 0.020 mole of NaOH is added to 1.00 L of each of the following solutions:

a. pure H2O
b. a mixture containing 0.100 M HC3H5O2 and 0.100 M NaC3H5O2