Reactions of Acids and Bases

Strength of Conjugate Acids and Bases The extent of the reaction between a Bronsted-Lowry acid and base depends on the strength of the acids and bases involved. The stronger an acid is, the weaker its conjugate base; the stronger a base is, the weaker its conjugate acid.

Predicting Reactions Using Acid Strength Example: Remember, that all four of the above acids and bases are all present at once in solution. Strong acids and strong bases are looking for each other. Since HClO4 is a very strong acid, ClO4- is a very weak base. For this reason, it cannot compete with the H2O for remaining HClO4’s. The reaction will continue exactly as it was originally drawn.

Example 2 In this situation we started with two relatively weak reactants. The CH3COOH will react with the H2O at first however, the acid and base produced H3O+ and CH3COO- are much stronger acids and bases. For this reason, the reaction is more likely to happen in the backwards direction. If the CH3COOH and the H2O do react, to form H3O+ and CH3COO- , the H3O+ and CH3COO- will react to go back as they began.

PROTON TRANSFER REACTIONS FAVOR THE PRODUCTION OF THE WEAKER ACID AND THE WEAKER BASE

Examples Is the forward or reverse reaction more favorable for the following reactions? Place either a forward or a backward arrow in your reaction to reflect your answer. Hydroiodic acid reacts with ammonia to form an ammonium ion and and iodide ion. Hydrosulfuric acid reacts with a chlorate ion to form chloric acid and a hydrosulfide ion. Water molecules react with other water molecules to produce hydronium ions and hydroxide ions.

Amphoteric Substances Any species that can act as both an acid or a base are described as amphoteric. Water is a common example of this. H2SO4(aq) + H2O(l)  H3O+(aq) + HSO4-(aq) NH3(g) + H2O(l) --> NH4+(aq) + OH-(aq) Which is water acting as a base? Which is water acting as an acid?

Strong Acid-Strong Base Neutralization Example: Hydrochloric acid and sodium hydroxide are both dissolved in separate beakers of water and then combined together. Analyze the products. Ionization of HCl in water: HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq) Dissociation of NaCl in water: NaOH(aq)  Na+(aq) + OH-(aq) H2O

Strong Acid-Strong Base Neutralization Cntd. HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq) and NaOH(aq)  Na+(aq) + OH-(aq) Once combined we now have a beaker with all four of the ions: H3O+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) --> Na+(aq) + Cl-(aq) + 2H2O(l) What are our spectator ions? H3O+(aq) + OH-(aq) --> 2H2O(l)

So what was produced in the neutralization reaction? Once combined we now have a beaker with all four of the ions: H3O+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) --> Na+(aq) + Cl-(aq) + 2H2O(l) H3O+(aq) + OH-(aq) --> 2H2O(l) Water was the first substance formed from the hydronium and hydroxide ions. A salt was also formed (NaCl). A salt is an ionic compound composed of a cation from a base and an anion from an acid.

Example In the reaction of chloric acid and magnesium hydroxide, a strong acid is neutralized with a strong base. What are the products formed? Was a salt produced?