Acids and Bases Chapter 19
Dr. Walker Properties of Acids and Bases Neutralization Reactions
HX + MOH H2O + MX Organizer Common Bases
NaOH Sodium Lye Hydroxide KOH Potassium Liquid Soaps Hydroxide
Mg(OH)2 Magnesium Milk of Hydroxide Magnesia (antacid)
Al(OH)3 Aluminum Maalox Hydroxide (antacid) Common Acids Common Acids Write text Defining Acids and Bases
• Arrhenius Acid/Base + + – Arrhenius Acid: Increases H3O (aka H , proton) concentration + - • HCl + H2O H3O + Cl
Write all Defining Acids and Bases
– Arrhenius Base: Increases OH- concentration • NaOH Na+ + OH-
– Problem • Some bases don’t have OH-!
Write all Defining Acids and Bases
• Bronsted-Lowry
– Acids: Proton Donor
– Bases: Proton Acceptor
– Proton: Hydrogen atom that has lost it’s electron (H+) Bronsted-Lowry + - NH3 + H2O NH4 + OH Base Acid Acid Base
• According to the Bronsted-Lowry definition, water acts as an acid because it gives up a proton! Strong and Weak Acids/Bases Strong and Weak Acids/Bases Strong Acid – dissociates completely in solution -Notice the HCl completely breaks apart -Tends to be smaller molecules
Weak Acid – dissociates partially in solution Notice the acetic acid stays mostly intact -Tends to be larger, organic molecules Electrolytes
• Solutions that can conduct electricity – Requires ions in solution (H+, Na+, Cl- , etc.) – Strong electrolytes • High ion content • Dissociate completely in solution (strong acids/bases) – Weak electrolytes • Lower ion content • Dissociate partially in solution (weak acids/bases) – Non-electrolytes • No dissocation, hence no ions in solution • Organic molecules Amphoteric
• Amphoteric – has properties of an acid and a base. Can act as either depending on situation
+ - • NH3 + H2O NH4 + OH – Water is the acid
+ - • H2O + HCl H3O + Cl – Water is the base
Self-Ionization of Water
+ - • H2O H + OH
– This happens in every glass of water
– This occurs in low enough concentration that it is not noticeable
– [H+] = [OH-] = 1.0 x 10-7 M
– [H+][OH-]= 1.0 x 10-14 M
Concentration
• Concentration is expressed in Molarity (M = moles/liter)
• Concentration is shown with [ ] brackets
• 0.1 = [HCl] – The HCl concentration is 0.1 M The pH Scale
• pH = power of Hydrogen • pH measures hydrogen ion concentration • The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the molarity of the H+ ion.
The pH Scale
• pH < 7 – Acidic • pH = 7 – Neutral • pH > 7 – Basic Calculating pH
• Works on powers of 10
• Scientific Notation
• Entering problems into the Calculator – Number Do not hit the multiply – EE (Ti-30) or exp ($ 1/Casio) button!!!!! It will mess you – Exponent up! – Solve by hitting “log”, “+/-”
Calculating pH
+ • pH = - log [H3O ]
Example: -5 [H3O] = 1.0 x 10 Note: This number is a molarity (or concentration!!) You’re given this most of the time, but you could have to calculate it! log [1.0 x 10-5] = -5 -log [1.0 x 10-5] = 5 pH = 5 Other Examples
• What is the pH of a 5.0 x 10-6 solution of sulfuric acid?
• What is the pH of a 1.4 x 10-10 solution of hydrochloric acid?
• What is the pH of a solution of HCl containing 0.1 moles and 2.5 L total volume? Other Examples • What is the pH of a 5.0 x 10-6 solution of sulfuric acid? – 5.0, ee/exp, 6, (+/-) – Log, (+/-) = 5.30 • What is the pH of a 1.4 x 10-10 solution of hydrochloric acid? = 9.85 • What is the pH of a solution of HCl containing 0.1 moles and 2.5 L total volume? – Find molarity, take – log of that – (-log [0.1/2.5]) = 1.40
+ Finding [H3O ] from pH
+ • You can perform the reverse and determine [H3O ] from p + -pH [H3O ] = 10
• What is the hydronium concentration of a solution with pH = 9.7 ?
+ -pH • [H3O ] = 10 + -9.7 • [H3O ] = 10 + -10 • [H3O ] = 1.99 x 10
Fighting the Calculator
• What is the hydronium concentration of a solution with pH = 9.7 ?
+ -pH • [H3O ] = 10 + -9.7 • [H3O ] = 10 – pH, (+/-), 2nd function, log + -10 • [H3O ] = 1.99 x 10
Examples
• What is the hydronium concentration of a solution with pH = 11.2?
• What is the hydronium concentration of a solution with pH = 1.9? Examples
• What is the hydronium concentration of a solution with pH = 11.2? 11.2, (+/-), 2nd function, log = 6.31 x 10-12
• What is the hydronium concentration of a solution with pH = 1.9? = 0.013 or 1.3 x 10-2 Note: For decimals with only a few zeros, the calculator won’t convert to scientific notation for you. pOH
• Measures Hydroxide (OH-) concentration • pOH = -log [OH-]
• pH + pOH = 14
• What is the pOH of a solution with a pH = 6.7? – pH + pOH = 14 – 6.7 + pOH = 14 – pOH = 7.3 pH Testing
• There are several ways to test pH – Blue litmus paper (red = acid) – Red litmus paper (blue = basic) – pH paper (multi-colored) – pH meter (7 is neutral, <7 acid, >7 base) – Universal indicator (multi-colored) – Indicators like phenolphthalein – Natural indicators like red cabbage, radishes
pH Indicators
• Indicators are dyes that can be added that will change color in the presence of an acid or base. • Some indicators only work in a specific range of pH • Once the drops are added, the sample is ruined • Some dyes are natural, like radish skin, red cabbage, and beets Common Chemical Indicators Indicators Indicator Questions • What is the pH of solution if bromothymol blue turns blue and thymol blue turns yellow? • A) 5.5 • B) 7.3 • C) 7.8 D) 8.7 Indicator Questions • Notice – bromothymol blue is blue above 7.6
• Thymol blue is yellow below 8.0
• The only choice that qualifies is c) 7.8
Titrations
• Titration: A method used to determine the unknown concentration of a substance in solution
– A buret is used for this
• Math involves a dilution calculation
– Remember, M1V1 = M2V2
Titrations
• Titrations use stoichiometry to determine endpoint of reactions (no I won’t make you do it)
• Equivalence point – # moles acid = # moles base in a titration
– If the proper indicator is chosen, the end point and equivalence point should be the same. Titrations
• How could you tell when a titration is finished? – Take the pH at given volume points with pH paper – Indicators: you need to use an indicator that turns color when your titration is complete. – End Point: Point in a titration where a color change takes place
Skills To Master
• Differentiating between acids and bases given specific properties • Calculating pH, [H+], and pOH given one of these values • Evaluating the proper indicator for a given pH range • Evaluating the pH given colorimetric results from indicators