Ch.16 - Aqueous Equilibrium See all chapters
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Ch.16 - Aqueous Equilibrium
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Weak Base Strong Acid Titrations

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Sections
Buffer
Acid and Base Titration Curves
Weak Acid Strong Base Titrations
Weak Base Strong Acid Titrations
Strong Acid Strong Base Titrations
Titrations of Diprotic and Polyprotic Acids
Ksp
Additional Practice
Equivalence Point
Acid Base Indicators
Selective Precipitation
Formation Constant
Additional Guides
Henderson Hasselbalch Equation
LearnAdditional Practice
Next SectionStrong Acid Strong Base Titrations

Whenever a WEAK BASE reacts with a STRONG ACID we use an ICF Chart to determine the pH of the solution. 

Weak Base Strong Acid Titrations

Concept #1: Understanding Weak Acid–Strong Base titration reactions

Concept #2: If you use an ICF Chart and at the end you have remaining weak acid and conjugate base then you have a buffer so you use the Henderson-Hasselbalch Equation to find pH. 

Concept #3: If any excess moles of the strong acid remain then we will use its concentration to find the pH of the solution. 

Concept #4: If the moles of both the conjugate base and strong acid are equal then we will have only weak acid at the end of our ICF Chart Calculation. To find pH we would follow up with an ICE Chart. 

Weak Base Strong Acid Titration Calculations

Example #1:

A buffer contains 167.2 mL of 0.25 M propanoic acid, CH3CH2COOH, with 138.7 mL of 0.42 M sodium propanoate, CH3CH2COONa. Find the pH after the addition of 150.2 mL of 0.56 M HCl. The Ka of CH3CH2COOH is 1.3 x 10-5.

 

Example #2: Calculate the pH of the solution that results from the mixing of 75.0 mL of 0.100 M NaC2H3O2 and 75.0 mL of 0.150 M HC2H3O2 with 0.0025 moles of HBr. Ka of HC2H3O2 is 1.8 x 10-5.    

Previous SectionWeak Acid Strong Base Titrations
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Additional Problems
The question below pertains to a titration where 0.30 M HNO 3 (in a buret) is added to 60.0mL of 0.40 M trimethylamine, (CH 3)3N (in the flask). How is the solution in the flask best characterized after 50. mL of the HNO 3 solution has been added? This is before equivalence point of the titration. (a) the solution is now a weak base (b) the solution is now a weak acid (c) the solution is now a strong base (d) the solution is now a strong acid (e) it is now a neutral solution (f) it is now a buffer solution
What is the pH of a 0.20 M NH 3/0.20 M NH4Cl buffer after 15 mL of 0.15 M HCl has been added to 65 mL of buffer?
A 250.0-mL solution buffer solution is 0.250 M in acetic acid and 0.250 M in sodium acetate. The acid dissociation constant of acetic acid is 1.8 x 10-5.  i. What is the initial pH of this solution?         ii. What is the pH after addition of 0.0050 mol of HCl?               iii. What is the pH after addition of 0.0050 mol of NaOH?
A 75.0-mL volume of 0.200 M NH 3 (Kb = 1.8 x 10-5) is titrated with 0.500 M HNO3. Calculate the pH after the addition of 13.0-mL of HNO3.
A 1.00 L buffer solution is 0.250 M in HF and 0.250 M in NaF. Calculate the pH of the solution after the addition of 100.0 mL of 1.00 M HCl. The Ka for HF is 3.5 × 10-4.  A) 3.09 B) 4.11 C) 3.82 D) 3.46 E) 2.78
In order to create a buffer 7.321 g of potassium lactate is mix with 550.0 mL of 0.328 M lactic acid, HC3H5O3. What is the pH of the buffer solution after the addition of 700.0 mL of 0.100 M hydrobromic acid, HBr? The Ka of HC3H5O3 is 1.4 x 10-4.
Consider the titration of a strong acid with a weak base. Which of the following statements is incorrect?  
A buffer contains 55.3 mL of 0.200 M nitrous acid, HNO 2, with 100.0 mL of 0.550 M sodium nitrite, NaNO2. Find the pH after the addition of 180.0 mL of 0.400 M HClO  4. The Ka of HNO2 is 4.6 x 10-4. 
What is the pH at the equivalence point of a weak base-strong acid titration if 20.00 mL of NaOCl requires 28.30 mL of 0.50 M HCl to reach the equivalence point? The acid dissociation constant of HOCl is 3.0x10-8. 3.76 0.30 3.18 4.03
Which of the following is the best choice to titrate 0.10 M C  6H5NH2? a) 0.30 M NaOH b) 0.01 M NH 3 c) 0.10 M HNO3 d) 0.10 M HCO2H
A 25.0 L solution is made of 0.10 M acid and 0.13 M conjugate base. What mass of HNO3 (MM = 63.01) in grams can the buffer absorb before one of the components is no longer present? A. 6.30 B. 8.19 C. 47.3 D. 157 E. 205
Consider the titration of 100.0 mL of 0.250 M aniline (Kb = 3.8 x 10  -10) with 0.500 M HCl. What is the pH of the solution at the stoichiometric point? A. -0.85 B. 8.70 C. 2.68 D. 11.62 E. none of these 
Pyradine (C6H5N) is a weak organic base with a K b of 1.7x10-9. Suppose you were to titrate 25.0 mL of a 0.100 M aqueous solution of pyridine with a 0.100 M HCl solution.  a. What is the pH at the equivalence point?                       b. The Ka of the acid-base indicator 2,3-dinitrophenol is around 6.69 x 10 -5, and the Ka of the acid-base indicator thymolphthalein is approximately 1.26x10-10. If you had to choose between these two indicators for your titration above, which would you choose?      
A student creates 150.00mL of a buffer that is 0.018 M in formic acid and 0.016 M in sodium formate. What would the pH of the buffer be after the addition of 15.00 mL of a 0.070 M HCl solution to the buffer?A. 3.69B. 3.85C. 4.18D. 1.15E. 3.30
Calculate the pH during the titration of 20.00 mL of 0.1000 M ammonia with 0.1000 M HCl(aq) after 15 mL of the acid have been added. Kb of ammonia = 1.8 x 10-5.
A 1.00 L buffer solution is 0.150 M in HC 7H5O2 and 0.250 M in LiC7H5O2. Calculate the pH of the solution after the addition of 100.0 mL of 1.00 M HCl. The Ka for HC7H5O2 is 6.5 x 10-5.
What is the pH of a 0.20 M NH 3/0.20 M NH4Cl buffer after 10 mL of 0.10 M HCl has been added to 65 mL of buffer?
A 25.0-mL sample of 0.125 M pyridine is titrated with 0.100 MHCl. Calculate the pH at equivalence point. Express your answer using two decimal places.
A 25.0-mL sample of 0.125 M pyridine is titrated with 0.100M HCl. Calculate the pH at 50 mL of added acid. Express your answer using two decimal places.
Which of the following occurs when HCl is added to a buffer containing (CH3)3N and (CH3)3NH+?  a. The concentration of (CH3)3N will increase.b. The concentration of (CH3)3NH+ will increase.c. The concentration of (CH3)3N will decrease.d. The concentration of (CH3)3NH+ will decrease.
20 mL of 0.25 M of NH 3 is titrated with 0.40 M HCl. Calculate the pH of the solution after 20 mL HCl is added. Kb (NH3) = 1.8 × 10 −5.a. 12.50b. 7.00c. 4.74d. 1.12
When a 0.25 M HCl solution reacts with 10.0 mL of a 0.30 M C  6H5NH2 solution the pH at the equivalence point will be:a) Less than 7.b) More than 7.c) Equal to 7.
Your job is to determine the concentration of ammonia in a commercial window cleaner. In the titration of a 25.00 mL sample of the cleaner, the equivalence point is reached after 16.85 mL of 0.138 M HCl has been added. What the initial concentration of ammonia in the solution? What is the pH of the solution at the equivalence point?