CHEM 112 Study Guide - Final Guide: Ph, Weak Base, Equilibrium Constant

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redant354

31 Mar 2019

School

UMASS-Amherst

Department

Chemistry

Course

CHEM 112

Professor

Prof. Scott M. Auerbach

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Document Summary

16. 4 estimating the ph of acid and base solutions. The ph of a solution containing a strong acid or strong base is calculated directly from the strong acid or strong base concentration. The ph of a solution containing a weak acid or weak base is calculated from the weak acid or weak base concentration and the equilibrium constant for the hydrolysis reaction of the weak acid or weak base. The acid base properties of a salt are determined by the hydrolysis reactions of the cation and anion that make up the salt. 16. 6 molecular structure and control of acid base strength. Relative acid base strength can be predicted or explained by the strength of the chemical bonds in the acid or base and the number of highly electronegative atoms in the acid or base . [oh ] = 10 poh (16. 6) pkw = ph + poh = 14. 00 at 25 c. Ka 5 3h3o1 4 3a2 4 3ha4 (16. 8)

Related Questions

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.)

periwinklegoat463

Salts formed by reaction of a strong acid with a weak base areacidic, and salts formed by reaction of a weak acid with a strongbase are basic. This is due to the equilibrium the conjugate haswith its acid or base. For example, sodium bicaronate NaHCO3contains the conjugate of the weak acid H2CO3. The conjugate willreform the acid through the equilibrium

HCO3?(aq)+H2O(aq)?H2CO3(aq)+HO?(aq)

and, thus, acts as a weak base. A solution of NaHCO3yields abasic solution.

If a salt is derived from a weak acid and a weak base, the pH ofthe solution depends on the relative acid strength (Ka) ofthe cation and base strength (Kb) of the anion. IfKa>Kb, the solution of the salt is acidic. IfKa<Kb, it is basic. If Ka?Kb, it is neutral.

Given that

Ka for HCN is 4.9

Unlike strong acids and bases that ionize completely in solution, weak acids or bases partially ionize. The tendency to ionize (i.e., the ionic strength) of a weak acid or base can be quantified in several ways including;

Ka or Kb, pKa or pKb, and percent ionization.

Benzoic acid is a weak acid that has antimicrobial properties. Its sodium salt, sodium benzoate, is a preservative found in foods, medications, and personal hygiene products. Benzoic acid dissociates in water:

C6H5COOH(aq)+H2O(l)âC6H5COOâ(aq)+H3Oâ(aq)

The pKa of this reaction is 4.2. In a 0.80 mol Lâ1 solution of benzoic acid, what percentage of the molecules are ionized?

Express your answer to two significant figures and include the appropriate units.

CHEM 112 Study Guide - Final Guide: Ph, Weak Base, Equilibrium Constant

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