5B3 Acid-Base Titrations

Question 1

Define:

neutralization reaction

Answer 1

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.

Question 2

What is the pH of the products of HCl + NaOH → H₂O + NaCl?

Answer 2

Neutral (pH = 7)

A strong acid reacts with a strong base to form a neutral salt and water.

Question 3

True or False:

A salt formed from neutralization retains properties of the acid or base.

Answer 3

False

Salt in a neutralization reaction does not inherit the properties of its reactants.

Question 4

What is the pH of a solution formed from a weak acid and strong base?

Answer 4

Basic (pH > 7)

The strong base’s characteristics dominate the reaction, making the solution basic.

Question 5

What is the pH of the product of a weak acid and a weak base reaction?

Answer 5

Neutral (pH = 7)

Example: Acetic acid reacts with ammonium hydroxide to form neutral salt and water.

Question 6

What type of solution forms when a strong acid reacts with a weak base?

Answer 6

An acidic solution with pH < 7.

The strong acid’s influence dominates the reaction, making the solution acidic.

Question 7

Give an example of a weak acid.

Answer 7

Acetic acid

(HC₂H₃O₂)

Acetic acid partially dissociates into H⁺ and C₂H₃O₂⁻ ions.

Question 8

True or False:

A strong base dissociates completely in water.

Answer 8

True

Example: NaOH dissociates fully into Na⁺ and OH⁻ ions.

Question 9

What is the general dissociation reaction of a weak acid?

Answer 9

HA ⇌ H⁺ + A⁻

Weak acids partially dissociate into hydrogen ions (H⁺) and anions (A⁻).

Question 10

Describe the reaction between a weak acid and a strong base.

Answer 10

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.

Question 11

Which ion forms when ammonia reacts with water?

Answer 11

Ammonium ion

(NH₄⁺)

NH₃ + H₂O ⇌ NH₄⁺ + OH⁻.

Question 12

List two strong bases.

Answer 12

1. Sodium hydroxide (NaOH)
2. Potassium hydroxide (KOH)

These bases fully dissociate in water, producing hydroxide ions (OH⁻).

Question 13

Fill in the blank:

The salt formed when acetic acid reacts with sodium hydroxide is _______.

Answer 13

Sodium acetate

(NaC₂H₃O₂)

The reaction forms water and sodium acetate as products.

Question 14

What is a titration?

Answer 14

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.

Question 15

Fill in the blank:

The titrant in a titration has a _______ concentration.

Answer 15

known

The known concentration of the titrant helps calculate the analyte’s concentration.

Question 16

What is the role of a burette in titrations?

Answer 16

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.

Question 17

How is the amount of titrant added recorded during titration?

Answer 17

By measuring the initial and final burette readings.

The difference between the readings gives the volume of titrant delivered.

Question 18

Define:

analyte

Answer 18

The solution with an unknown concentration that is analyzed during titration.

The titrant reacts with the analyte to determine its concentration.

Question 19

Which indicator is commonly used in titrations?

Answer 19

Phenolphthalein

Phenolphthalein is colorless in acidic solutions and turns pink in basic solutions.

Question 20

True or False:

Phenolphthalein turns pink at pH 7.

Answer 20

False

Phenolphthalein turns pink at a pH of 8.3.

Question 21

Define:

equivalence point

Answer 21

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.

Question 22

What is the endpoint in a titration?

Answer 22

The point where the indicator changes color, signifying the titration is complete.

The endpoint is ideally close to the equivalence point.

Question 23

True or False:

At the endpoint, pH always equals 7.

Answer 23

False

The pH depends on the strength of the acid and base.

Question 24

What equation is used to determine the concentration of an unknown solution at the equivalence point?

Answer 24

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.

Question 25

What is a **titration curve**?

Answer 25

A graph that plots pH (x-axis) **against the volume of titrant** added (y-axis). ## Footnote The equivalence point is the steep vertical section of the curve where neutralization occurs.

Question 26

Describe a titration curve representing a **weak acid-strong base titration**.

Answer 26

* Starts with an acidic pH * Slopes upward * Becomes vertical near equivalence * Ends with a basic pH ## Footnote The equivalence point is reached when moles of acid = moles of base.

Question 27

Which titration curve shows a **downward slope**?

Answer 27

Weak base-strong acid ## Footnote Example: NH₃ titrated with HCl starts at pH ≈ 11 and ends at pH ≈ 2.

Question 28

Why are weak acid-weak base titrations **rarely performed**?

Answer 28

They produce **curves with little inflection**, making data interpretation difficult. ## Footnote These titrations do not provide enough information for calculations.

Question 29

What is the **initial pH** of a weak base-strong acid titration curve?

Answer 29

pH < 7 ## Footnote The weak base dissociates partially, resulting in an initially basic solution.

Question 30

List *four* **steps to solve for pH** in a weak acid-strong base titration.

Answer 30

1. Write Ka expression 1. Set up ICE table 1. Solve for [H⁺] 1. Calculate pH ## Footnote Approximations can simplify calculations if dissociation is small.

Question 31

How is the **pH of a solution calculated** after titration?

Answer 31

pH = -log[H⁺] ## Footnote The [H⁺] concentration is derived using the Ka expression and ICE table.

Question 32

What does the **slope** of the titration curve **represent**?

Answer 32

The **rate of pH change** as titrant is added. ## Footnote Near the equivalence point, the slope increases sharply.

Question 33

What happens to **pH at the equivalence point** in a weak base-strong acid titration?

Answer 33

It **decreases sharply and then stabilizes** at an acidic pH. ## Footnote Example: NH₃ titrated with HCl ends with pH ≈ 2.

Question 34

What is the **stoichiometry at the equivalence point** of a weak acid-strong base titration?

Answer 34

1 mole of weak acid **reacts with 1 mole of strong base**. ## Footnote Example: 1 mol acetic acid (HC₂H₃O₂) reacts with 1 mol sodium hydroxide (NaOH).

Question 35

# Fill in the blank: A **weak acid titration curve** ends with a \_\_\_\_\_\_ pH.

Answer 35

basic ## Footnote Example: HC₂H₃O₂ titrated with NaOH ends with pH ≈ 12.

Question 36

What is the **pH at the equivalence point** for a strong acid-strong base titration?

Answer 36

7 ## Footnote In strong acid-strong base titrations, the products are neutral salt and water, resulting in a neutral solution.

Question 37

How is the pH of a solution affected when **excess titrant is added**?

Answer 37

The pH **shifts toward the pH of the excess reactant** (acidic or basic). ## Footnote Excess titrant changes the concentration of H⁺ or OH⁻ ions, altering the pH.

Question 38

How do you calculate the pH of a solution **after excess titrant is added**?

Answer 38

Find the **concentration of the excess reactant** and take the negative log of that concentration. ## Footnote For strong acids, use the formula pH = -log[H⁺]. For strong bases, use the formulas pOH = -log [OH⁻] and pH = 14-pOH