march 11

Chemistry Assignment Overview

• Due Date: Saturday, end before spring break.

• Focus on pattern recognition in acid-base chemistry.

Acid-Base Definitions and Reactions

• Acids, Bases, and Salts: Understand the definitions and be able to categorize substances appropriately.

Key Concepts

• H3PO4 (Phosphoric Acid):

  • Donates an H+ ion to water, leading to the formation of H3O+.

  • Can undergo multiple dissociations, losing one hydrogen ion at a time.

• Weak Bases:

  • Accept hydrogen ions; for example, NH2- acts as a weak base by acquiring H+ from water, forming OH-.

Proton Transfer Framework

• Recognize that reactions involve proton transfers without disassembly of entire molecules.

• Notably, focus on weak vs. strong acids and bases.

Analyzing Dissociation in Salts

• Dissociation:

  • Look for cation and anion formation in salts.

  • For instance, Chloroacetic Acid (Cl-CH2COOH) loses H+ to form Cl-CH2COO- and H3O+.

Spectator Ions

• Identify spectator ions that do not participate in the reaction, such as K+ or Na+.

• They can often be excluded from equilibrium calculations.

Assessing Acidity and Basicity

• NaHC6H6O6: Acts as a salt, showing both acidic and basic properties.

  • Depending on the environment, acts as either.

• Ascorbic Acid (H2C6H6O6):

  • Has two acidic protons, thus can also act as both an acid and base depending on its interaction in a solution.

pH Determinants

• Determine if a solution will be acidic, basic, or neutral based on the strength of the acid/base present.

• Understand that weak acids can behave as bases in the presence of a stronger acid.

Examples of Reactions

• HCl (Strong Acid):

  • Dissociates completely in water, producing H3O+ and Cl-.

• KNO3 (Salt):

  • Strong acid and base, yielding neutral solution with a pH of 7.

ICE Tables

• Use ICE tables to calculate equilibrium concentrations of acids and bases, particularly for weak solutions.

• Note when assumptions about negligible x (ionization) are valid (typically under 5% ionization).

Polyprotic Acids and Multiple Ka Values

• Understand polyprotic acids like phosphoric acid (H3PO4) and their dissociation steps (Ka1, Ka2, Ka3).

• Use the corresponding Ka values to derive pH or evaluate behavior in solution.

General Approach

• When determining the effect of solutes in solution:

  • Identify if it is an acid, base, or salt.

  • Determine dissociation and identify spectator ions.

  • Use appropriate Ka or Kb values based on the acid/base behavior observed.

  • Conduct equilibrium analysis when necessary, particularly for weak species.