C. W. BAKER HIGH SCHOOL Chemistry - Acids, Bases, Salts
General Terms
Electrolytes	Solutes which dissolve to form charged particles (ions) in solution. Electrolytes can be further subdivided into: · acids · bases · salts
Arrhenius Definition of an Acids	Solutes which dissolve in water to form hydronium ions (H3O^+). Examples of acids and their ionization in water are: 1. Hydrochloric Acid HCl + H20 ----->H3O^+(aq) + Cl^-(aq) 2. Nitric Acid HNO3 + H2O ----> H3O^+(aq) + NO3^- (aq) 3. Acetic Acid     HC2H3O2 + H2O ----> H3O^+(aq) + C2H3O2^- (aq) Acids tend to have similar properties because they all contain hydronium ions.
Arrhenius Definition of a Bases	Solutes which dissolve in water to form hydroxide ion (OH^-). Examples of bases and their ionization in water are: 1. Sodium Hydroxide NaOH (s) ----> Na^+(aq) + OH^-(aq) 2. Ammonia      NH3 + H20 -----> NH4^+(aq) + OH^-(aq) Bases tend to have similar properties because they all contain hydroxide ions.
Salts	Ionic substances which dissolve in water to form primarily ions other than hydronium or hydroxide. Examples of salts are: 1. Sodium Chloride NaCl (s) ------> Na^+ (aq) + Cl^- (aq) 2. Barium chloride BaCl2 (s) -----> Ba^+ (aq) + 2 Cl^- (aq)
Properties of Acids	Solutes which dissolve in water to form hydronium ions (H3O^+). Due to the fact that all acids produce the same ion in solution they have many common properties. Among these are: · Acids have a sour taste · Acids react with active metals to produce hydrogen gas and a salt. · Acids have a pH value less than 7. · Acids affect indicators (turn litmus paper red) · Acids neutralize bases (an acid + a base yields a salt + water)
Properties of Bases	Solutes which dissolve in water to form hydroxide ions (OH^-). Due to the fact that all acids produce the same ion in solution they have many common properties. Among these are: · Bases have a bitter taste. · Bases react with fats to produce soap in the saponification reaction. · Bases have a pH value greater than 7. · Bases affect indicators (turn litmus blue and phenylphthlein pink. · Bases neutralize acids.
Formation of Acids and Bases
Acid Anhydrides	Oxides of non-metals that react with water to form acids. · SO2   +   H2O    --->   H2SO3  (sulfurous acid)  *** · NOx    +   H2O   --->   HNO3   (nitric acid)        *** · CO2    +    H2O   --->   H2CO3  (carbonic acid)      *** These acid anhydrides are responsible for acid rain
Basic Anhydrides	Oxides of metals that react with water to form bases. · CaO   +   H2O   --->  Ca^2+(aq)    +    2 OH^-(aq) · Na2O  +   H2O   --->  2 Na^+(aq)   +   2 OH^-(aq)
The pH Scale
Definition and Calculation of pH	The term pH stands for the power of Hydrogen. However, the word power refers to the mathematical use of the word, that is, the exponent of the Hydrogen (or hydronium) ion concentration. The mathematical definition of pH is the negative logarithm of the hydronium ion concentration. The mathematical formula which expresses this relationship is: pH = - log [H3O^+] Examples: (Do you see why pH is the "power of hydrogen?) 1. If the [H3O^+] = 1 x 10^-5 then pH = 5 2. If the [H3O^+] = 1 x 10^-9 then pH = 9 3. If the [H3O^+] = 1 x 10^-7 then pH = 7 Note: A decrease of one pH unit indicates that the concentration of the hydronium ion increases 10x. (That is, an acid with a pH of 3 is ten times more acidic than an acid with a pH of 4, and 100 times more acidic than an acid with a pH of 5.
Self-Ionization of Water	In a sample of water, water molecules can react with each other to produce both hydronium ions and hydroxide ions according to the following reaction: H20 + H2O -----> H3O^+ + OH^- In this case, since water produces both the hydronium ions and hydroxide ions, water can be categorized as being both an acid and a base. Substances which can act as both an acid and a base are said to be amphiprotic or amphoteric. It may be helpful to think of a "see-saw" in trying to understand the relationship between the concentrations of hydronium and hydroxide ions. In pure water, the concentrations are equal, and so the "see-saw" is balanced. [H3O^+]  =  [OH^-] In an acidic solution, the concentration of hydronium becomes larger, while the concentration of hydroxide decreases: [H3O^+]   >  [OH^-] In a basic solution, the concentration of hydronium becomes smaller, while the concentration of hydroxide increases: [H3O^+] <  [OH^-]
pH of Acids	Since acids react with water to form hydronium ions, the concentration of hydronium ion in any acid will always be greater than the hydronium ion concentration in pure water: [H3O^+]acid > 1 x 10^-7M For this reason, the pH of any acid will always be less than 7. (Note: It's important to remember that the smaller the negative exponent, the greater the concentration. A concentration of 1 x 10^-4 is greater than a concentration of 1 x 10^-7)
pH of Bases	Since bases react with water to form hydroxide ions, which results in a decreases in the concentration of hydronium ion, the concentration of hydronium ions in base will always be less than the hydronium ion concentration in pure water. [H3O^+]base < 1 x 10^-7M For this reason, the pH of any base will always be greater than 7.
pH of Salts	Although salt primarily dissolve in water to form ions other than hydronium or hydroxide, they may (but don’t all) undergo secondary reactions which form either hydronium or hydroxide ions.  For this reason, some salt solutions will be neutral (pH=7), some may be acidic (pH<7), and some may be basic (pH>7).  The type of salt may be determined experimentally by testing the salt solution with litmus paper or universal pH paper.
Bronsted-Lowry Definition of Acids and Bases
Acid	An acid is defined as a substance which is a proton (H^+) donor.  Since all Arrhenius acids donate a proton to a water molecule in forming the hydronium ion, all Arrhenius acids would also qualify as Bronsted-Lowry acids.
Base	A base is defined as a substance which is a proton acceptor.  All Arrhenius bases also qualify as Bronsted-Lowry bases.