Podcast Beta
Questions and Answers
An acid is defined as a proton (H+) acceptor.
False
The hydronium ion (H3O+) represents highly solvated protons in water.
True
The weaker the acid, the lower its pKa value.
False
For any base B, the conjugate acid BH+ can also act as an acid.
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PH is calculated using the equation pH = -log10 [H3O+].
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The acidity of a solution is determined by the concentration of H2O in the solution.
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A strong acid corresponds to a high pKa value.
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Equilibrium constants for acid-base reactions can be replaced by concentrations in dilute solutions.
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The conjugate base of an acid is formed by the addition of a proton.
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The pKa of H3O+ at 25 °C is approximately -1.74.
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Study Notes
Acids and Bases
- An acid is a proton (H+) donor.
- A base is a proton (H+) acceptor.
- Brønsted acids and bases specifically refer to proton donors and acceptors.
- Lewis acids and bases are a more general definition:
- An acid is an electron-pair acceptor.
- A base is an electron-pair donor.
Protons in Water
- Protons are highly solvated in water.
- They are represented by the hydronium ion (H3O+).
Conjugate Acids and Bases
- AH + H2O → H3O+ + A− (AH: acid; A−: conjugate base)
- B + H2O → BH+ + HO− (B: base; BH+: conjugate acid)
- Acids can be neutral, cationic or anionic.
- Bases can be anionic, neutral or cationic.
Conjugate Acids of Bases as Acids
- For any base B, the conjugate acid (BH+) can be considered an acid in its own right.
General Equilibrium for Proton Transfer
- The transfer of a proton from an acid to a base in water can be represented by a general equilibrium equation.
- Equilibrium constant:
Ka = ([H3O+][Base]) / ([Acid][H2O])
Activity and Concentration
- Equilibrium constants (K) for acid-base equilibria are determined by the activities (a) of the components.
- In dilute solutions, activities can be approximated by concentrations.
Acidity of Aqueous Solutions
- The acidity of an aqueous solution is determined by its hydronium ion concentration ([H3O+]).
- Sørensen (1909) defined pH as
pH = -log10[H3O+]. - pH values range from 0 to 14.
- A lower pH indicates a higher acidity.
Acid Dissociation in Water
- The dissociation of an acid (AH) in water can be represented by the equilibrium equation:
AH + H2O ⇌ H3O+ + A− - Ka is the acidity constant for the acid AH.
pKa
-
pKa = -log10Ka - pKa measures the strength of an acid.
- Strong acids have high Ka values and low pKa values.
- Weak acids have low Ka values and high pKa values.
Polyprotic Acids
- Polyprotic acids have multiple ionizable protons.
- Example: H3PO4 (Phosphoric acid)
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Description
This quiz explores the fundamental concepts of acids and bases, including their definitions according to Brønsted and Lewis theories. It also covers protons in water, conjugate acids and bases, and the equilibrium of proton transfer in aqueous solutions. Test your understanding of these essential chemical principles!
