Unit C - Acids and bases

• • Solutions are made by dissolving solutes in water.
  • These  are called aqueous solutions. 
• • Water is the solvent most commonly used and is referred to as the “Universal Solvent”
• • Chemists work most commonly with liquid solutions. Why?

  1. Particles in the liquid phase are relatively mobile and can easily collide with one another to cause reactions

  • 2. It is an excellent solvent because of its polarity, small sized molecules, and hydrogen bonding
• • Solvation is what occurs when a solute dissolves. 
  • Negatively and positively charged ions become solvated that is, surrounded by solvent molecules
• • Polar substances dissolve ionic and polar compounds
  • Non-polar solvents dissolve non-polar compounds
  • “Like dissolves like”
• • Dissociation is the term used to describe the separation of ions (from a crystal lattice) when an ionic compound dissolves in water.
  • Dissociation is what occurs when an ionic compound is solvated.
• • Although dissociation represents the dissolving of an ionic compound in water, we do not write water in the equation as it is not consumed in the process of dissociation. 
  • Instead, once the compound has been dissociated, we change (s) to (aq).
• • As bases are ionic compounds, they dissociate just like other ionic compounds.
• • Acids do not dissociate, they ionize. 
• How do I know if a substance will dissociate/ ionize in water?

  • Ionic compounds→ use a solubility table
  • Molecular compounds → do not dissociate
  • Strong acids → fully ionize
  • Weak acids→ partially ionize
  • Stable Elements→ do not change
• • A solution is a homogeneous (the same, or uniform throughout) mixture of two or more substances. 
  • The particles in a solution are:
  • scattered randomly throughout the solution
  • in constant motion
• The substance that is present in larger quantity is the SOLVENT. 

  • The substance that is present in smaller quantity, which is dissolved in the solvent is the SOLUTE. 
• • Pure substances: consist of only one particular kind of matter. These are homogenous.
  •  There are two categories of pure substances

  1. ELEMENTS are pure substances, which can’t be broken down into simpler substances. 

  • Eg. Carbon (C), oxygen (O2), and Sulfur (S8)

  1. 2. COMPOUNDS are pure substances, which consist of two or more elements in combination.

  •  Eg. Water (H2O), carbon dioxide (CO2) and sodium chloride (NaCl) 
• • HETEROGENEOUS MIXTURE: is a non-uniform mixture, which consists of more than one phase
• • HOMOGENEOUS MIXTURE: only has one phase, and it is called a solution. It is uniform throughout. 
• • Solutions can be either electrolytes or nonelectrolytes
  • Electrolyte: conducts electricity in aqueous solution
  • Nonelectrolyte: does not conduct electricity in aqueous solution
• What makes something a conductor?

  • It must separate (dissociate) into its ions in solution.
• • Exothermic:
  • a chemical rxn  that releases energy to the surroundings  (lower energy bonds= stable)
  • Temp increases in surroundings
  • Endothermic:
  • a chemical rxn that absorbs energy from the surroundings (more energy stored in bonds)
  • Temp decreases in surroundings
• • Concentration is often represented by square brackets around the formula [NaCl] means concentration of sodium chloride solution in moles per litre (mol/L) or M
• • If we know the concentration of a solution, we can find the concentration of its ions via dissociation.
  • Step 1: write the balanced chemical equation for the dissociation of the ionic compound.
  • Step 2: multiply the concentration of the ionic compound by the coefficient of the ion in order to determine the ion concentration. 
  • Ratio = unknown/ known
• • As you increase the volume of a solution, its concentration decreases.
• • Solubility: the concentration of a saturated solution.
  • Every solubility value must be accompanied by a temperature value as temperature influences the rate at which a substance dissolves.
• • If all of the solute particles are dissolved, the solution is UNSATURATED 
  •  contains less than the maximum amount of solute than can dissolve in a given amount of solvent at a particular temperatur
• • SATURATED SOLUTION – a solution in which no more solute will dissolve at a specified temperature (maximum solute concentration).
• • SUPERSATURATED: when initially there is too much solute to dissolve.
  •  You heat up the solution, and then cool it down and all of  the solute dissolves. 
  • Supersaturated solutions are unstable, the addition of a small crystal or agitation may cause crystallization
• • Dynamic equilibrium occurs when crystallization and dissolving are occurring at the same rates.
• solid product of an aq soloution is called a precipiatate
• • Non-ionic/ molecular equation: an equation which shows all reactants and products in a reaction.
• • Total ionic equation: an equation which separates all ionic compounds into their ions as reactants and products.
• • Net ionic equation: the total ionic equation, however, eliminating like terms that are found both on the reactant and product side of the equation. 
• spectator ions - ions that are not involved in the reaction but are present in the solution
• Properties of Acids 

  • tart or sour taste 
  • squeaky to the touch
  • Acidic solutions are electrolytes 
  • Cause indicators to change color
  • Turns blue litmus paper red 
  • 1 – 6.9 on the pH scale
  • Acids react with some metals to produce hydrogen gas
  • Substance that produces hydrogen ions in solution, H+(aq) or H3O+(aq)
• • New definition= Modified Arrhenius: acids are substances that react with water to produce hydronium ions and an anion.  (IONIZATION)
• Properties of Bases

  • bitter taste 
  • slippery to the touch
  • Electrolytes
  • Cause indicators to change color
  • Turn red litmus paper blue 
  • 7.1 – 14 on the pH scale
  • Produces hydroxide ions in solution, OH-
• • Bases are compounds that dissociate to yield the hydroxide and a cation in aqueous solution.
• • All strong bases contain OH- (aq)
  • If a base does not contain a hydroxide ion, then it may take several steps to completely dissociate the base to produce an OH- (aq)
  • Step 1: separate the ionic compound into its ions
  • Step 2: add water to the anion to produce a hydroxide ion
• Can a substance act as an acid and a base?

  • Yes. We call these species amphiprotic.

  amphiprotic- having the ability to either accept or donate a proton (hydrogen ion)
• Neutralization

  • Reactions in which an acid and a base react in an aqueous solution to produce a salt and water.
  • double displacement reactions.
  • Neutralization can be identified as a reaction between hydronium and hydroxide ions to produce water.
  • If a solution containing hydronium ions (an acid) is mixed with a solution that has an equal amount of hydroxide ions, a neutral solution results.
• • The pH scale starts at 0 and goes to 14
  • Neutral is indicated by a pH of 7
  • A pH less than 7 indicates an acidic substance.
  • A pH greater than 7 indicates a basic substance. 
• • pH: power of hydrogen
  • pH has no units
  • The change in 1 pH unit changes the hydronium ion concentration increases by a factor of 10.