Predicting Reactions

Vocabulary Review for Aqueous Reactions Solvent – the substance present in the greatest quantity Solute – the substance being dissolved into the solvent Electrolyte – substance the dissociates into ions in water Ionic Compounds – a metal and nonmetal ionically bonded Solvation – the process of a dissociated ion being surrounded by water. This prevents the cations and anions from recombining and helps to stabalize the ions.

Ionic Compounds in Water Ionic compounds complete dissociate in water The ability of the electrons to move through water makes them excellent conductors.

Molecular Compounds in Water Molecules dissolved in water do not form ions, therefor, are not conductors. Exceptions: NH3(g) reacts with water to form NH4+(aq) and OH-(aq) HCl(g) in water ionizes to form H+(aq) and Cl-(aq)

Strong and Weak Electrolytes Strong Electrolytes are compounds whose aqueous solutions conduct electricity well. Ex: NaCl(aq)  Na+(aq) + Cl-(aq) Weak Electrolytes are compounds whose aqueous solutions conduct electricity poorly. These compounds are a mixture of ions and un-ionizes molecules in solution Ex: HC2H3O2 (aq) ⇋ H+(aq) + C2H3O2-(aq)

Precipitation Reactions Precipitate is an insoluble solid formed by a reaction in a solution Solubility is the amount of a given substance that can be dissolved in a given quantity of solvent at a given temperature. All ionic compounds of group 1 metals and the ammonium ion (NH4+) are soluble in water.

To Predict Precipitate Formation Note ions present in reaction Consider possible combinations of cations and anions Refer to solubility rules

Exchange (Metathesis) Reactions These are reactions involve the swapping of ions in solution. many precipitate and acid-base reactions exhibit this pattern AX + BY  AY + BX

Acid-Base Rections Acids are substances that are able to ionize in aqueous solution to form H+ ions. Ionization occurs when a neutral substance forms ions in solution Ex: HC2H3O2 (acetic acid) Since H+ is a naked proton, we refer to acids as proton donors.

Acid Ionization Different acids ionize to form different numbers of H+ Monoprotic acids ionize to form one H+ Diprotic acids ionize to form two H+ (this often occurs in 2 stages)

Base Ionization Bases are substances that react with the H+ ions formed by acids. Hydroxide ion, OH-, reacts with the H+ ions to form water Ex: H+(aq) + OH-(aq)  H2O(l)

Bases Compounds that do not contain OH- ions can also be bases Ex: Ammonia NH3(aq) + H2O(l) ⇋ NH4+(aq) + OH- This is a weak base (⇋) since only about 1% of NH3 ionizes

Strong and Weak Acids and Bases Strong acids and strong bases are strong electrolytes They completely ionize in solution COMMIT TO MEMORY TABLE 4.2 PAGE 130

Strong Bases All alkali metal hydroxides (group 1) Heavy alkaline earth metal hydroxides (group 2) Ca(OH)2, Ba(OH)2 and Sr(OH)2

Strong Acids Include HCl, HBr, HI, HClO3, HClO4, H2SO4 and HNO3 These acids ionize completely Note that polyatomic ions remain intact!

Identifying Strong Electrolytes Compounds can be classified as strong strong electrolytes, weak electrolytes or nonelectrolytes base on their solubility. Water soluble and ionic = strong electrolyte Water soluble, not ionic but strong acid = strong electrolyte Water soluble, not ionic but strong base = strong electrolyte

Identifying Weak Electrolytes If a compound is water soluble and not ionic, and is a weak acid or weak base, then it is a weak electrolyte.

Neutralization Reactions and Salts Neutralization Reaction occurs when an acid and a base react to produce water and a salt. Salt is any ionic compound whose cation comes from a base, and anion from an acid. Ex: Acid and metal hydroxide Mg(OH)2(s) + 2HCl(aq)  MgCl2(aq) + 2H2O(l) Net ionic Equation: Mg(OH)2(s) + 2H+  Mg2+(aq) + 2H2O(l)

Acid-Base Reactions with Gas Formation There are many bases besides OH- that react with H+ to form molecular compounds Carbonates and hydrogen carbonates (bicarbonates) will form CO2 gas when treated with an acid Ex: NaHCO3(s) + HCl(aq)  NaCl(aq) + H2O(l) + CO2(g) Net Ionic Equation: H+(aq) +HCO3(aq)  H2O(l) + CO2(g)