CHEM 1A Lecture Notes - Lecture 15: Hypobromous Acid, Conjugate Acid, Acid Strength

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goldhound747

6 Apr 2016

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Document Summary

Weak acids and bases, unlike their strong counterparts, do not dissociate fully. The extent of their dissociation is expressed by the magnitude of their dissociation constants, ka and kb, respectively. Expressions of the acid and base dissociation constants can be used to calculate the ph of a solution of a weak acid or base when their initial, analytical concentration is known. One of the dissociation products of a weak acid, ha, is its conjugate base, a-. The basicity of that base is inversely related to the acidity of its conjugate acid, ha. Weak acids generate relatively stronger weak bases and vice versa. The product of the acid and base dissociation constants for every conjugate acid-base pair is constant and is equal to kw. You should be able to: calculate the ph of weak acid and base solutions, calculate the ph of a conjugate base solution knowing its initial concentration and the acid dissociation constant of its conjugate acid.

Related Questions

For conjugate acid-base pairs, how are K_a and K_b related?

Consider the reaction of acetic acid in water.

where

a. Which two bases are competing for the proton?

b. Which is the stronger base?

c. In light of your answer to part b, why do we classify the acetate ion (CH₃CO₂^-) as a weak base? Use an appropriate reaction to justify your answer.

In general, as base strength increases, conjugate acid strength decreases. Explain why the conjugate acid of the weak base NH₃ is a weak acid.

To summarize, the conjugate base of a weak acid is a weak base and the conjugate acid of a weak base is a weak acid (weak gives you weak). Assuming K_a for a monoprotic strong acid is 1x10⁶, calculate K_b for the conjugate base of this strong acid. Why do conjugate bases of strong acids have no basic properties in water? List the conjugate bases of the six common strong acids. To tie it all together, some instructors have students think of Li⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, Sr²⁺, and Ba²⁺ as the conjugate acids of the strong bases LiOH, KOH, RbOH, CsOH, Ca(OH)₂, Sr(OH)₂, and Ba(OH)₂. Although not technically correct, the conjugate acid strength of these cations is similar to the conjugate base strength of the strong acids. That is, these cations have no acid properties in water; similarly, the conjugate bases of strong acids have no basic properties (strong gives you worthless). Fill in the blanks with the correct response. The conjugate base of a weak acid is a ______ base. The conjugate acid of a weak base is a ______ acid. The conjugate base of a strong acid is a ______ base. The conjugate acid of a strong base is a ______ acid. (Hint: Weak gives you weak and strong gives you worthless.)

limeswan13

For conjugate acid-base pairs, how are Ka and Kb related?

Consider the reaction of acetic acid in water:

CH₃CO₂H (aq) + H₂O (l) ⇌ CH₃CO₂⁻ (aq) + H₃O⁺ (aq) where Ka = 1.8 × 10⁻⁵

Which two bases are competing for the proton?
Which is the stronger base?
In light of your answer to part b. why do we classify the acetate ion (CH₃CO₂⁻) as a weak base? Use an appropriate reaction to justify your answer.
In general, as base strength increases, conjugate acid strength decreases. Explain why the conjugate acid of the weak base NH₃ is a weak acid.

To summarize, the conjugate base of a weak acid is a weak base and the conjugate acid of a weak base is a weak acid (weak gives you weak). Assuming Ka for a monoprotic strong acid is 1× 10⁶, calculate Kb for the conjugate base of this strong acid.

Why do conjugate bases of strong acids have no basic properties in the water?

List the conjugate bases of the six common strong acids.

To tie it all together, some instructors have students think of Li⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, Sr²⁺, and Ba²⁺ as the conjugate acids of the strong bases LiOH, KOH, RbOH, CsOH, Ca(OH)₂, Sr(OH)₂, and Ba(OH)₂. Although not technically correct, the conjugate acid strength of these cations is similar to the conjugate base strength of the strong acids. That is, these cations have no acidic properties in water; similarly, the conjugate bases of strong acids have no basic properties (strong gives you worthless). Fill in the blanks with the correct response. The conjugate base of a weak acid is a_____base. The conjugate acid of a weak base is a_____acid. The conjugate base of a strong acid is a_____base. The conjugate acid of a strong base is a_____ acid. ( Hint: Weak gives you weak and strong gives you worthless.)