Liquid Mixtures and Their Properties

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Questions and Answers

Which substances are combined to create an alkaline buffer solution with a pH of 9.25?

Ammonium hydroxide and ammonium chloride (correct)

Sodium hydroxide and sodium chloride

Potassium hydroxide and potassium bromide

Calcium hydroxide and calcium sulfate

What is the primary characteristic of the weak acid in a buffer solution?

It forms a strong acid when mixed

It is partly ionized (correct)

It is completely ionized

It has a higher pH than the buffer solution

What role does the salt play in a buffer solution?

It decreases the acidity of the solution

It neutralizes the weak acid completely

It completely ionizes in solution (correct)

It increases the overall pH to above 10

Which of the following statements about the pH of a buffer solution is true?

The pH can be influenced by the concentration of components Signup and view all the answers

What is the primary reaction occurring when an acid is added to the buffer solution?

Hydrogen ions combine with acetate ions to form acetic acid. Signup and view all the answers

In an alkaline buffer solution, what happens to the pH when a small amount of strong acid is added?

The pH decreases slightly Signup and view all the answers

What is the consequence of adding a base to the buffer solution?

Water is formed by the reaction of hydroxide ions and hydrogen ions. Signup and view all the answers

How does the buffer solution maintain pH stability when acid is added?

By neutralizing added hydrogen ions with acetic acid formation. Signup and view all the answers

What ion is primarily responsible for the reaction with hydroxide ions when a base is added?

Hydrogen ions Signup and view all the answers

Which statement best describes the relationship between acetic acid and acetate ions in the buffer system?

Acetic acid and acetate ions are in a constant state of formation and dissociation. Signup and view all the answers

What is the primary function of buffer solutions in relation to enzymes?

To maintain an optimum pH for enzyme activity Signup and view all the answers

What can occur if buffer solutions are absent from an enzymatic reaction?

Denaturation of the enzymes Signup and view all the answers

Which of the following statements correctly describes the consequences of not maintaining an appropriate pH for enzymes?

It can result in slowed enzyme action Signup and view all the answers

How can the absence of buffer solutions affect enzyme properties?

They can lead to loss in enzyme properties Signup and view all the answers

Which of the following is NOT a potential effect of lacking buffer solutions on enzymes?

Preservation of enzyme functionality Signup and view all the answers

What does the acid dissociation constant (Ka) represent in the ionization of a weak acid?

The ratio of the concentrations of the dissociated ions to the unionized acid Signup and view all the answers

In the equilibrium reaction HA + H2O ⇋ H+ + A−, what does HA represent?

A weak acid Signup and view all the answers

How is the pH of an acid buffer calculated?

pH = pKa + log ([salt]/[acid]) Signup and view all the answers

What would happen to the pH of an acid buffer if the concentration of the salt is increased while keeping the acid concentration constant?

The pH would increase Signup and view all the answers

In the context of the ionization of a weak acid, what does A− represent?

The conjugate base formed from the weak acid Signup and view all the answers

What is the formula used to calculate the pH of an acid buffer?

pH = pKa + log([salt]/[acid]) Signup and view all the answers

If the concentration of 'A-' is increased to 0.05 M while the concentration of HA remains the same, how does this affect the pH?

The pH increases Signup and view all the answers

What is the hydronium ion concentration when the pH equals 3.82?

1.51 x 10^-4 M Signup and view all the answers

What is the value of the pKa for the acid HA in this solution?

4 Signup and view all the answers

If the ratio of [salt] to [acid] changes to 1:1, what will the new pH be?

4.00 Signup and view all the answers

What is the formula to calculate the pH of a basic buffer solution?

pH = pKa + log([base]/[salt]) Signup and view all the answers

What relationship does pKa have with pKb for a weak base?

pKa + pKb = 14 Signup and view all the answers

When combining a weak base (B) with its salt (BA), what type of solution is formed?

Basic Buffer Signup and view all the answers

If a basic buffer solution has a pKa of 9, what would be the approximate pH when the concentration of the base is greater than that of the salt?

Greater than 9 Signup and view all the answers

In the context of buffer solutions, what does the term 'salt' refer to?

The conjugate acid of the weak base Signup and view all the answers

Signup and view all the answers

Study Notes

Liquid Mixtures

Liquid mixtures are combinations of two or more substances, where individual components retain their chemical identities.
Mixtures can be homogenous or heterogeneous.
Homogenous Mixtures (Solutions): Have uniform composition throughout.
- Examples: Saltwater, alcohol in water, vinegar.
- Solvent: The substance present in the largest amount.
- Solute: The substance dissolved in the solvent.
Heterogeneous Mixtures: Do not have uniform composition, and components are visually distinct.
- Examples: Oil and water, muddy water.

Properties of Liquid Mixtures

Miscibility: Describes whether two liquids mix. Water and ethanol are miscible, while oil and water are immiscible.
Boiling and Melting Points: Mixtures generally have different boiling and melting points compared to their pure components. This difference is due to interactions between the molecules.
Concentration: Indicates the amount of solute in a given amount of solvent. Expressed using terms like molarity or percentage.

Buffer Solutions

Buffer solutions are water-based solutions that resist changes in pH when small amounts of acid or alkali are added.
Composed of either a weak acid and its conjugate salt, or a weak base and its conjugate salt.
Resist pH changes upon dilution.

Types of Buffer Solutions

Acidic Buffers: Have a pH value below 7.
- Consist of a weak acid and a salt of a weak acid.
- Example: Sodium acetate and acetic acid (pH = 4.75).
Alkaline Buffers: Have a pH value above 7.
- Consist of a weak base and a salt of a weak base.
- Example: Ammonium hydroxide and ammonium chloride (pH = 9.25).

Buffering Action Mechanism

In a buffer solution, the salt is fully ionized, and the weak acid is partly ionized.
When acid is added, released protons are neutralized / removed by the acetate ions, re-forming acetic acid.
When a base is added, hydroxide ions are neutralized by hydrogen ions, forming water.

Preparation of Acid Buffers

A weak acid (HA) and its salt (KA) with a strong base (KOH) are combined.
HA ionizes, creating an equilibrium: HA + H₂O ⇌ H⁺ + A⁻
The acid dissociation constant (Ka) = [H⁺][A⁻]/[HA].
pH of acid buffer = pKa + log ([salt] / [acid])

Preparation of Base Buffers

A weak base (B) and its salt (BA) with a strong acid are combined.
pH of a basic buffer = pKa + log ([base] / [salt])
pKa + pKb = 14

Buffering Capacity

The buffering capacity is the amount of acid or base needed to change a litre of buffer by one pH unit.
B = millimoles/(ΔpH)

Examples of pH Calculations

Detailed examples of calculating pH values for various solutions.

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Description

Explore the fascinating world of liquid mixtures, where you will learn about homogenous and heterogeneous mixtures, their characteristics, and examples. Dive into the concepts of miscibility, boiling and melting points, and concentration to enhance your understanding of these essential chemical principles.