Recap of Solubility and Ionic Compounds

Solubility of Ionic and Covalent Compounds

Understanding the behavior of compounds in water is essential for predicting chemical reactions and solution properties.

• Soluble ionic solids dissociate into their constituent ions when dissolved in water.

• Soluble covalent compounds do not dissociate to form ions in water; they remain as molecules.

• Due to dissociation, the concentration of ions in solution can differ from the concentration of the compound itself.

• Insoluble ionic solids do not dissociate in water.

• In a precipitation reaction, soluble ionic reactants yield an insoluble solid product (precipitate), removing some dissolved ions from solution.

• Chemical equations can be written as molecular, ionic, or net ionic equations.

• Solubility guidelines are used to predict whether a compound will dissolve in water.

Acid-Base and Oxidation-Reduction Reactions

Conductance Measurements of Acids

Acids in aqueous solution can conduct electricity due to the presence of ions formed by dissociation.

• Strong acids such as hydrochloric acid (HCl) and nitric acid (HNO3) conduct electricity well.

• These acids dissociate in water to form protons:

Hydronium Ion Formation

The proton () does not exist freely in aqueous solution; it bonds to water to form the hydronium ion ().

• Acids dissociate in water to form hydronium:

• Both and notations are commonly used.

Conductance Measurements of Weak Acids

Weak acids, such as acetic acid (CH3CO2H), only partially dissociate in water and thus conduct electricity weakly.

• The double arrow indicates partial dissociation and equilibrium.

Strong vs Weak Acids

Acids are classified based on their degree of dissociation in water.

• Strong acids completely dissociate in water. Three important strong acids to memorize:

  • Hydrochloric acid:

  • Nitric acid:

  • Sulfuric acid:

• Weak acids partially dissociate in water. Example: acetic acid.

• The double arrow () is used for weak acids to indicate equilibrium.

Conductance Measurements of Bases

Bases in aqueous solution also conduct electricity due to the formation of hydroxide ions.

• Strong bases such as sodium hydroxide (NaOH) dissociate completely:

Conductance Measurements of Weak Bases

Weak bases, such as ammonia (NH3), only partially dissociate in water.

• Ammonia and ammonium hydroxide are both considered weak bases.

Strong vs Weak Bases

Bases are classified by their degree of dissociation in water.

• Strong bases completely dissociate. Five important strong bases to memorize:

• Weak bases partially dissociate. Ammonia is a representative weak base:

Acid-Base Reactions

Strong Acid-Strong Base Reaction

When a strong acid reacts with a strong base, the products are a salt and water.

• Salt is an ionic compound formed from the acid and base.

• Ionic equation:

• Net ionic equation:

Weak Acid-Strong Base Reaction

When a weak acid reacts with a strong base, the products are also a salt and water, but the weak acid is represented by its molecular formula.

• Ionic equation:

• Net ionic equation:

Acid-Base Titrations

Acid-base titration is a quantitative technique used to determine the concentration of an acid or base solution by neutralization with a standard solution.

• A standard solution has a known concentration.

• The equivalence point is reached when the number of moles of acid equals the number of moles of base.

• An indicator is used to signal the completion of the reaction by changing color.

Acid-Base Titration Example

Example: 5.00 mL NaOH sample of unknown concentration is titrated with 0.5631 M HCl. If 37.62 mL of HCl is required to neutralize the NaOH, what is the molarity of the NaOH sample?

• Step 1: Convert volume of HCl to moles using molarity.

• Step 2: Use the stoichiometry of the balanced equation to find moles of NaOH.

• Step 3: Calculate molarity of NaOH using its volume.

General titration strategy:

• Convert volume of standard to moles using molarity.

• Convert moles of standard to moles of unknown using balanced equation coefficients.

• Convert moles of unknown to molarity using its volume.

Oxidation-Reduction (Redox) Reactions

Definition and Electron Transfer

Oxidation-reduction reactions involve the net movement of electrons from one reactant to another.

• Oxidation is the loss of electrons.

• Reduction is the gain of electrons.

• Example:

• Calcium loses electrons (oxidized), bromine gains electrons (reduced).

Half-Reactions

Redox reactions can be split into two half-reactions to track electron transfer.

• Oxidation half-reaction:

• Reduction half-reaction:

• Reducing agent: The species that is oxidized (Ca in this example).

• Oxidizing agent: The species that is reduced (Br2 in this example).

Oxidation Numbers

Assigning oxidation numbers helps identify which species are oxidized and reduced.

• An atom in its elemental state has an oxidation number of 0.

• For monatomic ions, the oxidation number equals the ion's charge.

• Oxygen is usually -2, except in peroxides (e.g., H2O2), where it is -1.

• Hydrogen is usually +1, except in hydrides (e.g., NaH), where it is -1.

• The sum of oxidation numbers equals the charge of the molecule or ion.

Assigning Oxidation Numbers: Example

Example:

• Na: 0 (elemental) to +1 (in NaOH) → oxidized

• H in H2O: +1 to 0 (in H2) → reduced

Balancing Oxidation-Reduction Reactions

Redox reactions must be balanced for both mass and charge. The process involves several steps:

1. Determine oxidation numbers for all atoms in reactants and products.

2. Write the half-reactions and balance all atoms except H and O.

3. Balance O by adding H2O, then H by adding H+.

4. Balance charge by adding electrons ().

5. Multiply half-reactions by appropriate coefficients so electrons cancel; add and simplify.

6. If in basic solution, add OH- to neutralize H+, forming H2O.

Balancing Redox Reaction: Example

Example in acidic solution:

• Step 1: Assign oxidation numbers.

• Step 2: Write and balance half-reactions.

• Step 3: Balance O and H.

• Step 4: Balance charge with electrons.

• Step 5: Combine and simplify.

Summary Table: Strong Acids and Bases

Key Concepts Summary

• Acids dissociate in water to form protons ( or ).

• Bases dissociate in water to form hydroxide ().

• Strong acids and bases completely dissociate; weak acids and bases partially dissociate.

• Neutralization reactions can be used to determine concentrations via titration.

• Redox reactions involve electron transfer; oxidation is loss, reduction is gain of electrons.

• Reducing agent is oxidized; oxidizing agent is reduced.

• Oxidation numbers help identify redox changes.

• Redox reactions are balanced for mass and charge using a systematic procedure.