Acids and Bases in Chemistry

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What characterizes Lewis acids?

They are always weak acids.

They don’t accept lone pairs of electrons.

They can only be organic compounds.

They are electron-poor molecules or cations. (correct)

Why does an aqueous solution of FeCl3 turn out to be acidic?

Electron density flows towards the metal cation, weakening O-H bonds. (correct)

The hydrogen atoms in water become negatively charged.

It dissociates into FeCl2 and H2O.

FeCl3 is a strong base in water.

What conclusion can be drawn about weak acids and their conjugate bases?

Weak acids have weaker conjugate bases compared to strong acids.

The weaker the acid, the stronger its conjugate base. (correct)

The stronger the acid, the stronger its conjugate base.

Conjugate bases of weak acids are always strong acids.

How does the equilibrium lie for a strong acid like HCl in water?

The equilibrium lies on the far right. Signup and view all the answers

What is the characteristic of a weak acid in terms of dissociation?

It dissociates only partially in water. Signup and view all the answers

What is the role of water in the dissociation reaction 2 H2O(l) H3O+(aq) + OH-(aq)?

Water can act as both an acid and a base. Signup and view all the answers

Which of the following concentrations is correct for hydronium ions in pure distilled water at 25 oC?

1.0 × 10^-7 M Signup and view all the answers

What is the molarity of undissociated water in a liter of pure water?

55.4 M Signup and view all the answers

What is the ion product constant for water (Kw) defined as?

Kw = [H3O+][OH-] Signup and view all the answers

In the reaction HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq), what role does water play?

Water acts as a Bronsted-Lowry acid. Signup and view all the answers

According to Brönsted-Lowry theory, which of the following correctly describes a Brönsted-Lowry acid?

A substance that donates a proton Signup and view all the answers

What is the role of NH3 in the reaction where it interacts with H2O as described by Brönsted-Lowry theory?

Bronsted-Lowry base Signup and view all the answers

Which pair represents a conjugate acid-base pair according to Brönsted-Lowry theory?

H2O and OH- Signup and view all the answers

What defines a Lewis acid?

A lone pair acceptor Signup and view all the answers

In the context of Lewis acids and bases, what is the role of BF3 when reacting with NH3?

Lewis acid Signup and view all the answers

Which of the following statements about the Brönsted-Lowry theory is correct?

It cannot explain reactions involving substances like FeCl3. Signup and view all the answers

What is a characteristic of a strong acid compared to a weak acid?

It completely dissociates in solution. Signup and view all the answers

Which of the following is true regarding the dissociation of distilled water?

Distilled water can dissociate into H+ and OH- ions. Signup and view all the answers

What is the role of water in acid-base reactions according to the definitions provided?

It can act as either a base or an acid. Signup and view all the answers

Which of the following statements about acids and bases is true?

Lewis acids accept lone pairs of electrons. Signup and view all the answers

How does the dissociation of strong acids differ from weak acids?

Strong acids dissociate completely, while weak acids dissociate only partially. Signup and view all the answers

What is the interpretation of Kw at 25°C?

It represents the product of the concentrations of H+ and OH- ions in water. Signup and view all the answers

Which method can be used to measure pH?

The use of a universal indicator or electronic pH meter. Signup and view all the answers

What is the molarity of a solution containing 1000 g of a substance with a molar mass of 18.02 g/mol in 1.00 L?

55.4 M Signup and view all the answers

At a temperature of 25 °C, what is the value of the ion-product constant, Kw?

1.0 × 10−14 Signup and view all the answers

How can pH be measured with high accuracy?

By using a pH electronic meter Signup and view all the answers

What is the pH range that indicates a basic solution?

pH > 7 Signup and view all the answers

Which statement is true regarding the use of methyl orange as an indicator?

It turns yellow at pH levels above approximately 4.2. Signup and view all the answers

What pH level is considered neutral?

pH = 7 Signup and view all the answers

What will a solution with a yellow color when tested with bromocresol purple indicate?

pH is between 4.2 and 5.6 Signup and view all the answers

What is the approximate pH of a solution that is yellow with both methyl orange and bromocresol purple?

Between 4.2 and 5.6 Signup and view all the answers

What is the pH of a 0.050 M hydrochloric acid solution?

1.30 Signup and view all the answers

Which formula is used to find the concentration of hydronium ions from hydroxide concentrations?

[H3O+] = Kw / [OH-] Signup and view all the answers

What is the molarity of sodium hydroxide in a 100.0 mL solution made from dissolving 2.50 g of NaOH?

0.625 M Signup and view all the answers

Why do alkaline-earth metal hydroxides have lower pH values compared to alkali metal hydroxides, despite being strong bases?

They are not fully soluble. Signup and view all the answers

If 5.00 g of Ca(OH)2 is dissolved in 1250.0 mL of solution, what is the pH of the resulting solution?

13.03 Signup and view all the answers

How does the degree of dissociation of strong diprotic acids compare to strong monoprotic acids?

Strong diprotic acids can have both strong and weak dissociations. Signup and view all the answers

What is the final pH of a solution where [H3O+] = 1.60 × 10^-14?

13.80 Signup and view all the answers

What will happen to the pH if a strong acid is mixed with a strong base in equal concentrations?

The solution will have a neutral pH. Signup and view all the answers

Study Notes

Acids and Bases 1

Two definitions of acids and bases are examined: Brønsted-Lowry and Lewis.
Brønsted-Lowry theory defines an acid as a proton (H⁺) donor and a base as a proton acceptor.
An example of a Brønsted-Lowry acid-base reaction is shown with water and ammonia.
In this reaction, water acts as an acid and ammonia acts as a base.
Another example of a Brønsted-Lowry reaction is given with sulphuric acid and water.
The Brønsted-Lowry theory has a disadvantage: it doesn't explain highly acidic solutions resulting from substances that aren't proton donors, such as FeCl₃.
Lewis theory defines a Lewis acid as a lone pair acceptor and a Lewis base as a lone pair donor.
An example illustrates a Lewis acid-base reaction where ammonia donates a lone pair to boron trifluoride.
Another example shows the reaction between hydroxide and hydrogen chloride, where hydroxide acts as a Lewis base and hydrogen chloride acts as a Lewis acid.
Lewis definitions are more comprehensive than previous definitions of acids and bases.
These definitions are widely used in organic chemistry.
Aqueous solutions of FeCl₃ are acidic because the hydrogen atoms in water are attracted to the metal cation, weakening their bonds with oxygen, which can then be abstracted by water molecules to form more H₃O⁺ ions.

Brønsted-Lowry Theory - Revision Slide

In the Brønsted-Lowry theory example, H₂O donates a proton (H⁺ ion) to NH₃, making water a Brønsted-Lowry acid.
In turn, NH₃ accepts a proton, making it a Brønsted-Lowry base.
The reverse reaction shows a conjugate acid-base pair. NH₄⁺ donates a proton (H⁺ ion) to hydroxide (OH⁻), making NH₄⁺ a Brønsted-Lowry acid and OH⁻ a Brønsted-Lowry base.
In summary, conjugate acid-base pairs are formed by an acid and a base in an equilibrium reaction.

Strong and Weak Acids

A strong acid dissociates completely in water.
The equilibrium lies to the right for strong acids.
Strong acids have a very large equilibrium constant (HCl, for example).
The conjugate base of a strong acid is very weak.

Weak Acids

Weak acids dissociate only partially in water.
The equilibrium for weak acids lies towards the left.
Weak acids have a very small equilibrium constant, for example acetic acid.
The conjugate base of weak acids is relatively strong.

Strengths of Acids and Their Conjugate Bases

A table displays the relative strengths of various acids and their conjugate bases.
The table is ordered from strong acids to weak acids.
The stronger the acid, the weaker its conjugate base.
The weaker the acid, the stronger its conjugate base.

Dissociation of Water

Water is amphoteric, acting as both an acid and a base.
Water as a base accepts protons (H⁺ ions), for example, when reacting with hydrochloric acid.
Water as an acid donates protons (H⁺ ions), for example, when reacting with ammonia.
A reaction between two water molecules illustrates how one water molecule acts as an acid and the other acts as a base, forming hydronium (H₃O⁺) and hydroxide (OH⁻) ions.

Water Dissociation

Distilled water is a weak electrolyte.
The concentration of hydronium ions ([H₃O⁺]) and hydroxide ions ([OH⁻]) in distilled water at 25 °C is 1.0 × 10⁻⁷ M.
Two molecules in a billion dissociate.

Ion-Product Constant

The ion-product constant (K_w) of water is a measure of the equilibrium between water molecules, hydronium (H₃O⁺) and hydroxide (OH⁻).
K_w = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25ºC
The concentrations of [H₃O⁺] and [OH⁻] in pure water are equal, making it neutral.
Solutions with greater [H₃O⁺] than [OH⁻] are acidic, and basic solutions have a higher [OH⁻] concentration than [H₃O⁺].

The pH Scale

pH is a measure of the acidity or basicity of a solution.
pH = -log[H₃O⁺]
Acidic solutions have pH values less than 7.
Neutral solutions have a pH of 7.
Basic solutions have pH values greater than 7.
Values for pH can be negative or greater than 14, which depends on temperature.

pH of Some Common Substances

A chart shows the pH values of common substances.

Measuring pH

pH can be measured using an electronic meter, which is highly accurate.
The electronic meter requires calibration with solutions of known pH like distilled water or buffer solutions.
Acid-base indicators can also approximate pH.
Universal indicators (paper strips or liquid) are another way to measure pH, offering relatively less precise measurements compared to the electronic meter.

pH for Strong Acids

Strong monoprotic acids dissociate completely in water.
Use the initial concentration of the strong acid to calculate [H₃O⁺], which is used to determine pH.

pH for Strong Bases

Alkali metal hydroxides (MOH) dissociate almost completely in water, producing metal cations (M⁺) and hydroxide anions (OH⁻) in a 1:1 molar ratio.
The concentration of hydroxide ions ([OH⁻]) can be used to calculate [H₃O⁺] and then pH.

Strong Bases (continued)

Some alkaline-earth metal hydroxides, while being strong bases, do not completely dissociate; this results in fewer hydroxide ions, impacting their pH to become lower.
Metal oxides like CaO react with water to form alkaline solutions.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores key concepts related to acids and bases, including the characteristics of Lewis acids, the behavior of strong and weak acids, and the role of water in dissociation reactions. It also covers Brönsted-Lowry theory and related equilibrium concepts. Test your understanding of these fundamental topics in chemistry!