Unit 14: Acids & Bases Chapter 19

Review: Naming an Acid Binary acids (H + nonmetal): hydro ______ic acid Ternary acids (H + polyatomic ion): –ate ions: _________ic acid –ite ions: _________ous acid Name the following acids: HBr H2SO3 H3PO4 Write the formulas for the following acids: Hydrosulfuric acid Nitrous acid Chromic acid

Definition of Bronsted-Lowry Acid A chemical species that is able to lose or "donate" a hydrogen ion (aka proton because the H+ contains no electrons or neutrons)  Acid loses a hydrogen ion

Properties of Acids Taste sour Corrosive Feel watery Are electrolytes: conduct an electrical current by forming H+ ions in solution pH < 7

Review: Naming a Base Formula is name + “hydroxide”: Metal + OH- Ammonium + OH- Name the following bases: NaOH NH3 Ca(OH)2 Write the formulas for the following bases: Magnesium hydroxide Aluminum hydroxide Lithium hydroxide 5

Definition of Bronsted-Lowry Base A chemical species that is able to gain or "accept" a hydrogen ion (aka proton because the H+ contains no electrons or neutrons)  Base gains a hydrogen ion

Properties of Bases Taste bitter Corrosive Feel slippery Are electrolytes: conduct an electrical current by forming OH- ions in solution pH > 7 7

Indicators Indicators: organic substances that change colors in an acid or a base (sometimes paper, sometimes liquids) Acids turn… Litmus paper – red Phenolphthalein – clear Universal indicator – red/orange Bases turn… Litmus paper – blue Phenolphthalein – pink Universal indicator – blue

Household Items & the pH Scale

pH and pOH Scale Measured on a numeric scale from 0-14 This scale number indicates ion concentration of a solution It is much easier to work numbers 0-14 than with than the actual range of 1 to 10–14 (0.00000000000001) In an acidic solution, [H+] > [OH-] In a basic solution, [H+] < [OH-] pH + pOH = 14 pH pOH Stands for “power of hydrogen” Stands for “power of hydroxide” Shows the [H+] in a solution Shows the [OH-] in a solution pH = -log[H+] pOH = -log[OH-]

pH and pOH Scale [H+] and [OH-] are inverses: the exponents always add up to -14 Ex: If [H+] = 1.0x10-3M, then [OH-] = 1.0x10-11M

pH and pOH Calculations Notice the relationship between concentration and the pH / pOH value: Toothpaste has a hydrogen ion concentration of 10–10M, so its pH is 10. pH = -log[10-10] = 10 Pure water, which is neutral, has a pH of 7. That means its hydrogen ion concentration is 10–7M. 7 = -log[H+] ; [H+] = 10-7

pH & pOH Practice In a NaOH solution the pH = 11. What is the [H+] of the solution? If a substance’s pH = 3, what is the pOH? Find the pH and pOH of a 0.1M HNO3 solution. If the [H+] = 1x10-4M, what is the [OH-]? What is the pH and pOH? 11 = -log[H+] ; [H+] = 10-11 M 3 + pOH = 14 ; pOH = 11 pH = -log[0.1] = 1 1 + pOH = 14 ; pOH = 13 1x10-4 + [OH-] = 1x10-14 ; [OH-] = 1x10-10 pH = -log[1x10-4] = 4 & pOH = -log[1x10-10] = 10 (once you get pH, you can just subtract from 14 to get pOH) 13

Strength of Acids and Bases Determined by how much they ionize (dissociate) in water Strong – ionize 100% in water Weak – only partially ionize in water Complete dissociation - all HCl compounds have separated into H+ and Cl- ions Partial dissociation - some HNO2 compounds have separated into H+ and NO2- ions, while some remain together

Strength of Acids and Bases The terms weak and strong are used to compare the strengths of acids and bases The terms dilute and concentrated are used to compare the concentration of solutions They do not mean the same thing! The combination of strength and concentration ultimately determines the behavior of the acid or base.

Strength of Acids and Bases Strong Acids: Only HNO3, HI, HBr, HCl, H2SO4, HClO4 Remember: NO, I Brought Claude SOme ClOthes All other acids are weak, and remain in equilibrium Ex: HNO2 ↔ H+ + NO2- Strong Bases: Group I or II metals Ex: NaOH, Mg(OH)2…etc. All other bases are weak, and remain in equilibrium Ex: NH3 + H2O ↔ NH4+ + OH-

Conjugate Acids & Bases Conjugate acids are formed when a base accepts a proton (H+) Conjugate bases are formed when an acid donates a proton (H+)

Conjugate Strength Example: Strong Acid = weak conjugate base Strong Base = weak conjugate acid Weak Acid = strong conjugate base Weak Base = strong conjugate acid Example: HCl + NH3 → Cl- + NH4+ (strong acid) (weak base) (weak conjugate base) (strong conjugate acid)

Conjugate Practice Label the acid (A), base (B), conjugate acid (CA) & conjugate base (CB). NH3 + HNO3 → NH4+ + NO3- CH3OH + NH2- → CH3O- + NH3 OH- + H3O+ → H2O + H2O NH2- + H2O → NH3 + OH- B A CA CB A B CB CA B A CA CB B A CA CB

Neutralization Neutralization: the reaction of an acid and a base; products are salt and water Example: consuming antacid products, which are basic, neutralizes stomach acid 20

Neutralization Example: sodium hydroxide (base) and hydrochloric acid (acid) react to form sodium chloride (salt) and water.

Neutralization Practice Neutralizations are double displacement reactions! Practice predicting products (always a salt and water): Example #1 __Ca(OH)2 + __H3PO4 → ? Example #2 __Fe(OH)2 + __HBr → ? __Ca(OH)2 + __H3PO4 → __Ca3(PO4)2 + __H2O 3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O __Fe(OH)2 + __HBr → __FeBr2 + __H2O Fe(OH)2 + 2HBr → FeBr2 + 2H2O 22

Titration Titration – determining the concentration of a base by using an acid whose concentration is known. 1. An indicator (phenolphthalein) is added to the standardized acid (acid of known concentration). 2. The unknown base is added until the solution is neutralized and reaches the equivalence point (where [H+] is equal to [OH-]). 3. Adding one more drop of base changes the color of the solution to pink. This is called the endpoint. * The equivalence point is not necessarily the midpoint, or the point where pH = 7

Titration Calculations MaVa(#H+) = MbVb(OH-) M = concentration (molarity) V = volume (L or mL) (#H+ or OH-) = number of ions Example: It took 75mL of NaOH to neutralize 50mL of 2M HCl. What is the concentration of the NaOH? MaVa(#H+) = MbVb(#OH-) (2M)(50mL)(1) = (x)(75mL)(1) x = 1.33M NaOH

Titration Practice Practice: It took 20mL of Ca(OH)2 to neutralize 25mL of 0.05M HCl. What is the concentration of the base? MaVa(#H+) = MbVb(#OH-) (0.05M)(25mL)(1) = (x)(20mL)(2) x = 0.031 M

Definition of Arrhenius’ Acids & Bases Acids/bases are determined by what type of ions they produced Arrhenius Acids produce H+ ions in solution Monoprotic acids – have 1 ionizable hydrogen Diprotic acids – have 2 ionizable hydrogens Triprotic acids – have 3 ionizable hydrogens Arrhenius Bases produce OH- in solution Produces H+ ions in solution Produces OH- ions in solution