-a base contains an OH group and ionizes in solutions to produce OH - ions: Neutralization: Hydrogen ions (H + ) in solution form

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1 NOTES Acids, Bases & Salts Arrhenius Theory of Acids & Bases: an acid contains hydrogen and ionizes in solutions to produce H+ ions: a base contains an OH group and ionizes in solutions to produce OH ions: Neutralization: Hydrogen ions (H + ) in solution form BronstedLowry Theory of Acids & Bases: an acid is a base is Examples: Conjugate acidbase pairs differ by one proton (H+) A conjugate acid is the particle formed when a base gains a proton. A conjugate base is the particle that remains when an acid gives off a proton. Examples: In the following reactions, label the conjugate acidbase pairs: a) H 3PO 4 + NO 2 HNO 2 + H 2PO 4 b) CN + HCO 3 HCN + CO 3 2 c) HCN + SO 3 2 HSO 3 + CN d) H 2O + HF F + H 3O + notice that water can act as both an acid and a base according to the Bronsted Lowry theory (depending on what it is reacting with); it is said to be AMPHOTERIC. Properties of Acids and Bases: ACIDS: BASES:

2 Strength of Acids and Bases: a strong acid dissociates completely in sol n: a weak acid dissociates only partly in sol n: a strong base dissociates completely in sol n: a weak base dissociates only partly in sol n: The Lewis Theory of Acids & Bases acid: electron pair. base: electron pair. neutralization: Examples: ionization of NH 3: autoionization of water: reaction of NH 3 with HBr (is a Lewis AND a BronstedLowry acidbase reaction): AcidBase Reactions Neutralization reactions: reactions between acids and metal hydroxide bases which produce. H + ions and OH ions combine to form water molecules:

3 Example: the reaction of HCl and NaOH (there are 3 ways to write the chem. eq.): 1) balanced formula unit equation: 2) total ionic equation: 3) net ionic equation: Example: Write the 3 types of equations for the reaction of hydrobromic acid, HBr, with potassium hydroxide, KOH. 1) 2) 3) Example: Write the 3 types of equations for the reaction of calcium hydroxide, Ca(OH) 2, with nitric acid, HNO 3. 1) 2) 3) Notes: ph and poh Experiments have shown that pure water ionizes very slightly: Measurements show that: Pure water contains equal concentrations of H 3O + and OH, so it is neutral. ph is a measure of the concentration of hydronium ions in a solution: Example: What is the ph of a solution where [H 3O + ] = 1 x 10 7 M? When an acid is added to water, the [H 3O + ] increases, and the ph decreases.

4 Example: What is the ph of a solution where [H 3O + ] = 1 x 10 5 M? When a base is added to a solution, the [H 3O + ] decreases, and the ph increases. Example: What is the ph of a solution where [H 3O + ] = 1 x M? The ph scale: poh is a measure of the concentration of hydroxide ions in solutions: Example: What is the poh of a solution where [OH ] = 1 x 10 5 M? At every ph, the following relationships hold true: 1) What is the ph of a solution where [H 3O + ] = 3.4 x 10 5 M? 2) The ph of a solution is measured to be What is the [H 3O + ] in this solution? 3) What is the ph of a solution where [H 3O + ] = 5.4 x 10 6 M? 4) What is the [OH ] and poh for the solution in #3?

5 Acids & Bases: Titrations The amount of acid or base in a solution is determined by carrying out a neutralization reaction; an appropriate acidbase indicator (changes color in specific ph range) must be used to show when the neutralization is completed. This process is called a TITRATION: the addition of a known amount of solution to determine the volume or concentration of another solution. 3 steps: 1) add a measured amount of an acid of unknown concentration to a flask. 2) add an appropriate indicator to the flask (i.e. phenolphthalein) 3) Add measured amounts of a base of known concentration using a buret. Continue until the indicator shows that neutralization has occurred. This is called the end point of the titration. Example: A 25 ml solution of H 2SO 4 is neutralized by 18 ml of 1.0 M NaOH using phenolphthalein as an indicator. What is the concentration of the H 2SO 4 solution? Equation: H 2SO 4 + 2NaOH Na 2SO 4 + 2H 2O 1) How many mol of NaOH are needed for neutralization? 2) How many moles of H 2SO 4 were neutralized? 3) Calculate the concentration of the acid: Titration Curve: a graph showing how the ph changes as a function of the amount of added titrant in a titration. data for the graph is obtained by titrating a solution and measuring the ph after every drop of added titrant. Sample titration curve:

6 **Equivalence point = the point on the curve where the moles of acid equal the moles of base; the midpoint of the steepest part of the curve (the most abrupt change in ph) is a good approximation of the equivalence point. knowledge of the equivalence point can then be used to choose a suitable indicator for a given titration; the indicator must change color at a ph that corresponds to the equivalence point. Calculations of Titrations: 1) The Mole Method & Molarity Calculate the molarity of a sulfuric acid solution if 23.2 ml of it reacts with g of Na 2CO 3. Na 2CO 3 + H 2SO 4 Na 2SO 4 + CO 2 + H 2O 2) Normality the normality (N) of a solution is defined as the molarity x the total positive oxidation number of the solute. Examples: HCl H + + Cl H 2SO 4 2H + + SO 4 2 NaOH Na + + OH Ba(OH) 2 Ba OH Example: Calculate the molarity and normality of a solution that contains 34.2 g of Ba(OH) 2 in 8.00 L of solution. **1 equivalent of an acid reacts with 1 equivalent of a base, so in titration problems, you can use this equation: N av a = N bv b (norm. acid)(vol. acid) = (norm. base)(vol. base) Example: 30.0 ml of N HNO 3 required 22.5 ml of Ca(OH) 2 for neutralization. Calculate the normality and molarity of the Ca(OH) 2 solution. 2HNO 3 + Ca(OH) 2 Ca(NO 3) 2 + 2H 2O