Chemistry Chapter 5: Aqueous Solutions

Chapter 5: Reactions in Aqueous Solution

• Aqueous solutions involve ionic compounds reacting in water.
• Examples include KMnO4 in water, forming K+(aq) + MnO4-(aq).
• Ionic compounds dissolve in water, with water molecules surrounding the ions (cations and anions).
• Examples include CuCl₂ in water.
• Aqueous solutions can conduct electricity due to the presence of ions, making them electrolytes.
• Strong electrolytes like HCl, CuCl₂, and NaCl dissociate completely into ions.
• Weak electrolytes like acetic acid only partially ionize.
• Nonelectrolytes like sugar and ethanol dissolve in water but do not conduct electricity.

Water Solubility of Ionic Compounds

• Compounds containing ions like Na+, K+, and NH₄⁺ are generally soluble in water.
• Compounds containing ions like Cl⁻, Br⁻, I⁻, and F⁻ are typically soluble unless paired with certain metal cations such as Ag+, Hg₂²⁺, Pb²⁺, or Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺ and Pb²⁺.
• Salts of sulfate (SO₄²⁻) are generally soluble, with exceptions for Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺.
• Many metal carbonates and sulfides, phosphates, oxalates, and chromates are insoluble.
• Exceptions for solubility exist for various salts, including those of NH₄⁺ and alkali metal cations, or other specific metal ions e.g. Ba(OH)₂.
• Common insoluble anions include sulfides, carbonates, phosphates, and those forming many metal oxides and hydroxides that aren't specifically noted as exceptions.

Acids

• Acids release H⁺ ions in water.
• Strong acids like HCl, H₂SO₄, HClO₄, and HNO₃ fully dissociate.
• Weak acids like acetic acid (CH₃CO₂H) partially dissociate.
• Nonmetal oxides can act as acids by reacting with water (e.g., CO₂ + H₂O → H₂CO₃).

Bases

• Bases release OH⁻ ions in water.
• Strong bases like NaOH fully dissociate.
• Weak bases like ammonia partially dissociate.
• Metal oxides can be bases (e.g., CaO + H₂O → Ca(OH)₂).

Net Ionic Equations

• Net ionic equations show only the species directly involved in a reaction, omitting spectator ions.
• Spectator ions are not involved in the reaction itself.
• Precipitation, acid-base, and gas-forming reactions are examples of exchange reactions.

Quantitative Aspects of Reactions in Solution

• Molarity (M) is the moles of solute per liter of solution.
• Molarity is used to calculate the concentration of a solution.
• Preparing a solution involves accurate weighing of solutes and dissolving them in a specific volume of solvent.
• Diluting an existing solution involves adding more solvent to decrease the concentration.

Types of Reactions in Water

• Exchange reactions involve the exchange of ions between reactants.
• Precipitation reactions form an insoluble product.
• Acid-base reactions produce water.
• Gas-forming reactions yield a gaseous product.
• Redox reactions involve electron transfer.

Redox Reactions

• Redox reactions involve a change in oxidation states.
• Oxidation represents an increase in oxidation number.
• Reduction represents a decrease in oxidation number.
• Oxidizing agents gain electrons, while reducing agents lose electrons.

Oxidation Numbers

• Oxidation numbers indicate the assigned charge of an atom in a compound.
• Rules for assigning oxidation numbers include considering the charge of an ion and the charge of hydrogen in most compounds, common for some elements like H, O, etc
• Oxidation numbers in free elements are zero.

Titrations

• Titrations are used to determine the unknown concentrations of certain substances by gradually reacting them with a solution of known concentration.
• An indicator is used to mark the equivalence point, where the reactants have reacted completely.