5B3 Acid-Base Titrations Flashcards
Interpret titration curves to determine data such as equivalence points and endpoints.
Define:
neutralization reaction
A reaction where an acid and a base react to form water and a salt.
This occurs when hydrogen ions and hydroxide ions combine to produce water.
What is the pH of the products of HCl + NaOH → H₂O + NaCl?
Neutral (pH = 7)
A strong acid reacts with a strong base to form a neutral salt and water.
True or False:
A salt formed from neutralization retains properties of the acid or base.
False
Salt in a neutralization reaction does not inherit the properties of its reactants.
What is the pH of a solution formed from a weak acid and strong base?
Basic (pH > 7)
The strong base’s characteristics dominate the reaction, making the solution basic.
What is the pH of the product of a weak acid and a weak base reaction?
Neutral (pH = 7)
Example: Acetic acid reacts with ammonium hydroxide to form neutral salt and water.
What type of solution forms when a strong acid reacts with a weak base?
An acidic solution with pH < 7.
The strong acid’s influence dominates the reaction, making the solution acidic.
Give an example of a weak acid.
Acetic acid
(HC₂H₃O₂)
Acetic acid partially dissociates into H⁺ and C₂H₃O₂⁻ ions.
True or False:
A strong base dissociates completely in water.
True
Example: NaOH dissociates fully into Na⁺ and OH⁻ ions.
What is the general dissociation reaction of a weak acid?
HA ⇌ H⁺ + A⁻
Weak acids partially dissociate into hydrogen ions (H⁺) and anions (A⁻).
Describe the reaction between a weak acid and a strong base.
The weak acid donates a H⁺ ion to the OH⁻ ion of the strong base, forming water and a salt.
Example: HC₂H₃O₂ + NaOH → H₂O + NaC₂H₃O₂.
Which ion forms when ammonia reacts with water?
Ammonium ion
(NH₄⁺)
NH₃ + H₂O ⇌ NH₄⁺ + OH⁻.
List two strong bases.
- Sodium hydroxide (NaOH)
- Potassium hydroxide (KOH)
These bases fully dissociate in water, producing hydroxide ions (OH⁻).
Fill in the blank:
The salt formed when acetic acid reacts with sodium hydroxide is _______.
Sodium acetate
(NaC₂H₃O₂)
The reaction forms water and sodium acetate as products.
What is a titration?
A technique used to determine the concentration of an analyte in a solution using a titrant.
A titrant has a known concentration, and the analyte’s concentration is calculated by reaching the equivalence point.
Fill in the blank:
The titrant in a titration has a _______ concentration.
known
The known concentration of the titrant helps calculate the analyte’s concentration.
What is the role of a burette in titrations?
It delivers precise volumes of the titrant into the unknown solution.
The burette allows controlled addition of the titrant, enabling accurate determination of the equivalence point.
How is the amount of titrant added recorded during titration?
By measuring the initial and final burette readings.
The difference between the readings gives the volume of titrant delivered.
Define:
analyte
The solution with an unknown concentration that is analyzed during titration.
The titrant reacts with the analyte to determine its concentration.
Which indicator is commonly used in titrations?
Phenolphthalein
Phenolphthalein is colorless in acidic solutions and turns pink in basic solutions.
True or False:
Phenolphthalein turns pink at pH 7.
False
Phenolphthalein turns pink at a pH of 8.3.
Define:
equivalence point
The point at which the moles of acid and base in a titration are equivalent (1:1 ratio).
The equivalence point is visually identified by a sharp change in the titration curve or a color change in the pH indicator.
What is the endpoint in a titration?
The point where the indicator changes color, signifying the titration is complete.
The endpoint is ideally close to the equivalence point.
True or False:
At the endpoint, pH always equals 7.
False
The pH depends on the strength of the acid and base.
What equation is used to determine the concentration of an unknown solution at the equivalence point?
Mt * Vt = Mu * Vu
Where Mt is the concentration of the titrant, Vt is the volume of titrant added, Vu is the volume of the unknown solution, and Mu is the unknown concentration.
What is a titration curve?
A graph that plots pH (x-axis) against the volume of titrant added (y-axis).
The equivalence point is the steep vertical section of the curve where neutralization occurs.
Describe a titration curve representing a weak acid-strong base titration.
- Starts with an acidic pH
- Slopes upward
- Becomes vertical near equivalence
- Ends with a basic pH
The equivalence point is reached when moles of acid = moles of base.
Which titration curve shows a downward slope?
Weak base-strong acid
Example: NH₃ titrated with HCl starts at pH ≈ 11 and ends at pH ≈ 2.
Why are weak acid-weak base titrations rarely performed?
They produce curves with little inflection, making data interpretation difficult.
These titrations do not provide enough information for calculations.
What is the initial pH of a weak base-strong acid titration curve?
pH < 7
The weak base dissociates partially, resulting in an initially basic solution.
List four steps to solve for pH in a weak acid-strong base titration.
- Write Ka expression
- Set up ICE table
- Solve for [H⁺]
- Calculate pH
Approximations can simplify calculations if dissociation is small.
How is the pH of a solution calculated after titration?
pH = -log[H⁺]
The [H⁺] concentration is derived using the Ka expression and ICE table.
What does the slope of the titration curve represent?
The rate of pH change as titrant is added.
Near the equivalence point, the slope increases sharply.
What happens to pH at the equivalence point in a weak base-strong acid titration?
It decreases sharply and then stabilizes at an acidic pH.
Example: NH₃ titrated with HCl ends with pH ≈ 2.
What is the stoichiometry at the equivalence point of a weak acid-strong base titration?
1 mole of weak acid reacts with 1 mole of strong base.
Example: 1 mol acetic acid (HC₂H₃O₂) reacts with 1 mol sodium hydroxide (NaOH).
Fill in the blank:
A weak acid titration curve ends with a ______ pH.
basic
Example: HC₂H₃O₂ titrated with NaOH ends with pH ≈ 12.
What is the pH at the equivalence point for a strong acid-strong base titration?
7
In strong acid-strong base titrations, the products are neutral salt and water, resulting in a neutral solution.
How is the pH of a solution affected when excess titrant is added?
The pH shifts toward the pH of the excess reactant (acidic or basic).
Excess titrant changes the concentration of H⁺ or OH⁻ ions, altering the pH.
How do you calculate the pH of a solution after excess titrant is added?
Find the concentration of the excess reactant and take the negative log of that concentration.
For strong acids, use the formula pH = -log[H⁺].
For strong bases, use the formulas pOH = -log [OH⁻] and pH = 14-pOH
