Chapter 4: Types of Reactions and Solution Stoichiometry

Water is the most common solvent.

  • Hydration is the process by which the positive ends of water molecules are attracted to the negatively charged anions and the negative ends of water molecules are attracted to positively charged cations. (similar to dissolving)

  • hydration process: the positive part of water (H+) is attracted to the negative ion, the negative part of water (O2-) is attracted to positive ions

  • The solubility of ionic substances in water varies greatly.

  • delta/partial positives and negatives are based on electronegativity and used only in covalent bonds

  • electronegativity - when bonded, some atoms have a stronger pull on shared electrons

  • “like dissolves like”

  • solutions are made up of a solvent and a solute

polar molecule: a molecule with unequal charge distribution

hydroxide: in ionic compounds (ex. NaOH)

hydroxide group: in covalent compounds (ex. C5H5OH)

solute: the substance being dissolved - in the lesser amount

solvent: the substance doing the dissolving - in the greater amount

Electrical conductivity

electrical conductivity: the ability to conduct an electric current

  • strong electrolytes conduct current very efficiently

  • weak electrolytes are poor conductors

  • nonelectrolytes do not conduct electricity

  • Svante Arrhenius was the first to correctly identify the basis for the conductivity properties of solutions

  • to conduct an electric current, you must have charged particles that are free-flowing (not bonded)

- Strong Electrolytes - soluble salts, strong acids, strong bases

  • strong acids: HCl, HBr, HI, HNO3, H2SO4, HClO4

  • strong bases: group 1 bases, Ca(OH)2, Sr(OH)2, Ba(OH)2, Ra(OH)2

  • (Li and down on group 1, Ca and down on group 2)

- Weak Electrolytes - weak acids, weak bases, and partially soluble salts

  • Weak acids and weak bases dissociate (ionize) only to a slight extent in aqueous solutions

  • weak acid - HC2H3O2

  • weak base - NH3

  • although nonelectrolytes dissolve, the entire molecule remains intact (no dissociation)

    - steps to make a dilution/solution:

    • measure out solute

    • add a little bit of distilled water to the bottom of your volumetric flask

    • add solute to the flask

    • add more, but not all, of the water needed

    • mix

    • add the rest of the distilled water, up to the volume marker

  • moles of solute after dilution = moles of solute before dilution

  • the solution becomes less concentrated (molarity decreases, volume increases, indirect relationship)

  • dilution equation: M1V1 = M2V2 (1 - stock solution 2- resulting solution)

Types of Chemical Reactions

  • types of solution reactions: precipitation reactions (DR), acid-base reactions (DR), oxidation-redaction reactions (SR, Combination, Combustion, Decomposition)

Precipitation Reactions

  • two solutions are mixed and an insoluble substance forms

  • AB +CD —> AD + CB (all ionic compounds)

Solubility Rules

  • NO3- salts are soluble

  • most salts containing group 1 metals or NH+ are soluble

  • most SO42- salts are soluble (but not with Ba Pb Hg or Ca)

  • most hydroxides are insoluble unless paired with a group 1 metal

  • most Cl-, BR-, and I- salts are soluble (not with Ag+ or Pb2+)

Acid-Base Reactions

  • Arrhenius’s concept of acids and bases is that an acid is a substance that produces (H+) ions when dissolved in water while a base is a substance that produces (OH-) when dissolved in water

  • Bronsted-Lowery concept of Acids and Bases is that an acid is a proton (H+) donor and a base is a proton (H+) accepter

  • Strong Acid + Strong Base: anion from the acid and cation from the base spectate. The salt formed is always soluble, and the net ionic equation is always H+ + OH- —> H2O

  • Weak Acid + Strong Base: net ionic equation includes the undissociated weak acid

  • OH- is such a strong base that it can be assumed to react completely with any acid

  • neutralization reactions occur when just enough base is added to react exactly with the acid in solution

  • Acid-Base Titrations

    • Volumetric analysis - a technique used for determining the amount of a certain substance by doing a titration

    • titration - delivery (from a buret) of a measured volume of a solution of known concentration (the titrant) into a solution containing the substance being analyzed (the analyte)

    • equivalence point or stoichiometric point -

molecular equations: gives the overall reaction stoichiometry but not necessarily the actual forms of the reactants and products in solution

complete ionic equation: represents as ions all reactants and products that are strong electrolytes

net ionic equation: includes only those solution components undergoing a change. Spectator ions are not included.

standard solution: a solution whose concentration is accurately known

Molarity (M): moles of solute per volume of solution in liters ( = moles solute/liters solution)

nonelectrolytes: substances that dissolve in water but do not produce any ions (ex. ethanol - C2H5OH and table sugar (C12H22O11)

strong electrolytes: substances that completely ionize when they are dissolved in water

strong electrolytes: substances that exhibit a small degree of ionization in water

aliquot: sample of/portion of

dilution: adding (distilled) water to a stock solution to achieve the desired concentration