Chapter Aqueous Reactions

Aqueous Solutions  Aqueous solutions are solutions in which water is the dissolving medium. Use (aq) for the state of a substance dissolved in water.  Remember that a solution is a homogenous mixture of at least two substances.  Solvent: substance present in greater quantity  Solute: substance dissolved in the solvent  Aqueous solutions are solutions in which water is the dissolving medium. Use (aq) for the state of a substance dissolved in water.  Remember that a solution is a homogenous mixture of at least two substances.  Solvent: substance present in greater quantity  Solute: substance dissolved in the solvent

Electrolytic Properties  Electrolytes: substances that produce ions in aqueous solutions. Ionic compounds are generally good electrolytes because they break down into ions. Electrolytes conduct electricity.  Ex: Put NaCl into water and it breaks apart into Na + and Cl - ions surrounded by water molecules.  Electrolytes: substances that produce ions in aqueous solutions. Ionic compounds are generally good electrolytes because they break down into ions. Electrolytes conduct electricity.  Ex: Put NaCl into water and it breaks apart into Na + and Cl - ions surrounded by water molecules.

Strong and Weak Electrolytes  Strong electrolytes: dissolve almost completely into ions; good electrical conductors.  Ex: HCl (aq)  H + (aq) + Cl - (aq)  Weak electrolytes: exist in water mostly as molecules; only a slight formation of ions.  Ex: HC 2 H 3 O 2 (aq)  H + (aq) + C 2 H 3 O 2 - (aq)  Strong electrolytes: dissolve almost completely into ions; good electrical conductors.  Ex: HCl (aq)  H + (aq) + Cl - (aq)  Weak electrolytes: exist in water mostly as molecules; only a slight formation of ions.  Ex: HC 2 H 3 O 2 (aq)  H + (aq) + C 2 H 3 O 2 - (aq)

Nonelectrolytes  Nonelectrolytes: substances that do not form ions when placed in water.  Most molecular compounds dissolve without forming ions. Water molecules simply come in between individual molecules. No ions are formed.  Nonelectrolytes will not conduct electricity. Ex: pure water, sucrose solution  Note: Acids are molecules but will form ions in aqueous solution!  Nonelectrolytes: substances that do not form ions when placed in water.  Most molecular compounds dissolve without forming ions. Water molecules simply come in between individual molecules. No ions are formed.  Nonelectrolytes will not conduct electricity. Ex: pure water, sucrose solution  Note: Acids are molecules but will form ions in aqueous solution!

Acids  Acids are substances that ionize in aqueous solution to form H + ions.  If the amount of H + increases, pH decreases (pH < 7).  H + = a proton, so acids are often called “proton donors”.  Therefore, all acids will have hydrogen in the formula, usually written at the beginning. Always include (aq) with an acid formula!  Acids are substances that ionize in aqueous solution to form H + ions.  If the amount of H + increases, pH decreases (pH < 7).  H + = a proton, so acids are often called “proton donors”.  Therefore, all acids will have hydrogen in the formula, usually written at the beginning. Always include (aq) with an acid formula!

Monoprotic and Polyprotic Acids  Monoprotic acids: yield one H + ion per molecule of acid. Ex: HCl (aq)  Diprotic acids: yield two H + ions per molecule of acid. Ex: H 2 SO 4(aq)  1st step: H 2 SO 4(aq)  H + (aq) + HSO 4 - (aq)  2nd step: HSO 4 - (aq)  H + (aq) + SO 4 2- (aq)  Triprotic Acids: yield three H + ions per molecule of acid. Ex: H 3 PO 4 (aq). These acids would have three steps to remove the hydrogen ions from the molecule.  Monoprotic acids: yield one H + ion per molecule of acid. Ex: HCl (aq)  Diprotic acids: yield two H + ions per molecule of acid. Ex: H 2 SO 4(aq)  1st step: H 2 SO 4(aq)  H + (aq) + HSO 4 - (aq)  2nd step: HSO 4 - (aq)  H + (aq) + SO 4 2- (aq)  Triprotic Acids: yield three H + ions per molecule of acid. Ex: H 3 PO 4 (aq). These acids would have three steps to remove the hydrogen ions from the molecule.

Bases  Bases produce OH - ions in aqueous sol’n, making the pH higher than 7.  Bases are known as “proton acceptors”.  All hydroxides (NaOH, KOH) are bases, but not all bases are hydroxides.  For example, NH 3 is a base because it produces hydroxide ion in water: NH 3(aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq)  Bases produce OH - ions in aqueous sol’n, making the pH higher than 7.  Bases are known as “proton acceptors”.  All hydroxides (NaOH, KOH) are bases, but not all bases are hydroxides.  For example, NH 3 is a base because it produces hydroxide ion in water: NH 3(aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

Strong Acids and Strong Bases  Strong acids and strong bases are strong electrolytes.  Memorize these strong acids: HCl, HBr, HI, HClO 3, HClO 4, HNO 3, H 2 SO 4  Memorize these strong bases (meat cleaver): LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH) 2, Sr(OH) 2, and Ba(OH) 2  Acids and bases not listed above are considered weak acids or bases and are weak electrolytes. Non-soluble bases are NON ELECTROLYTES  Strong acids and strong bases are strong electrolytes.  Memorize these strong acids: HCl, HBr, HI, HClO 3, HClO 4, HNO 3, H 2 SO 4  Memorize these strong bases (meat cleaver): LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH) 2, Sr(OH) 2, and Ba(OH) 2  Acids and bases not listed above are considered weak acids or bases and are weak electrolytes. Non-soluble bases are NON ELECTROLYTES

Table 4.3: Electrolytic Behavior

Strong, Weak, or Nonelectrolytes? CaCl 2 Strong: soluble ionic cmpd HNO (aq) Strong: strong acid C 2 H 5 OHNonelectrolyte: molecule KOHStrong: soluble ionic cmpd NH 3 Weak: weak base H 3 PO 4(aq) Weak: weak acid

Neutralization Reactions  Neutralization reactions are double replacement reactions in which we mix an acid with a base.  The mixing of a strong acid and a strong base will produce a salt and water.  HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l)  Salt: any ionic cmpd whose cation comes from a base and whose anion comes from an acid.  Neutralization reactions are double replacement reactions in which we mix an acid with a base.  The mixing of a strong acid and a strong base will produce a salt and water.  HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l)  Salt: any ionic cmpd whose cation comes from a base and whose anion comes from an acid.

Acid-Base Reactions With Gas Formation  Other bases besides hydroxides will react with acids to form salts and gases with low solubility in water.  Sulfides react with acids to form hydrogen sulfide gas. 2HCl (aq) + Na 2 S (aq)  H 2 S (g) + 2NaCl (aq)  Carbonates and bicarbonates react with acids to form carbon dioxide gas. HCl (aq) + NaHCO 3(aq)  NaCl (aq) + H 2 CO 3(aq)  H 2 O (l) + CO 2 (g) (At normal room temperature and pressure carbonic acid will decompose into water and carbon dioxide.)  Other bases besides hydroxides will react with acids to form salts and gases with low solubility in water.  Sulfides react with acids to form hydrogen sulfide gas. 2HCl (aq) + Na 2 S (aq)  H 2 S (g) + 2NaCl (aq)  Carbonates and bicarbonates react with acids to form carbon dioxide gas. HCl (aq) + NaHCO 3(aq)  NaCl (aq) + H 2 CO 3(aq)  H 2 O (l) + CO 2 (g) (At normal room temperature and pressure carbonic acid will decompose into water and carbon dioxide.)