Unit 13 Acids and Bases

A. Properties & Examples electrolyte turn litmus red sour taste slippery feel turn litmus blue bitter taste sticky feel electrolyte react with bases to for water and a salt (ionic compound) react with acids to for water and a salt (ionic compound)

Acids Affect Indicators: Blue litmus paper turns red in contact with an acid.

Bases affect indicators: Red litmus paper turns blue in contact with a base. Phenolphthalein turns pink in a base.

ACIDS: Most citrus fruits, tea, battery acid, vinegar, milk, soda, apples. BASES: Common household bases include baking soda, lye, ammonia, soap, and antacids.. A. Properties & Examples

B. Definitions There are 3 definitions used to describe acids and bases: Arrhenius Br Ø nsted-Lowry Lewis The most traditional is Arrhenius acids and bases.

B. Definitions Arrhenius - In aqueous solution…Arrhenius - In aqueous solution… HCl + H 2 O  H + + Cl – –Acids –Acids form hydrogen ions (H + ) H HHHH H Cl OO – + acid Also called hydronium ions (H 3 O + )

B. Definitions Arrhenius - In aqueous solution…Arrhenius - In aqueous solution… –Bases –Bases form hydroxide ions (OH - ) NH 3 + H 2 O  NH OH - H H H H H H N NO O – + H H H H base

B. Definitions Brønsted-LowryBrønsted-Lowry HCl + H 2 O  Cl – + H 3 O + –Acids –Acids are proton (H + ) donors. –Bases –Bases are proton (H + ) acceptors. conjugate acid conjugate base baseacid Amphoteric - can be an acid or a base.Amphoteric - can be an acid or a base. Conjugate acid – particle formed when a base gains a H + Conjugate base – particle that remains when an acid has donated a H + Another common way to refer to hydrogen ions is to call them “protons”

B. Definitions LewisLewis –Acids –Acids are electron pair acceptors. –Bases –Bases are electron pair donors. Lewis base Lewis acid

Practice Questions 1.When you wafted a substance your nose burned. Would this substance be an acid or a base? 2.A hydrogen ion (H + ) can also be called a _________ or ____________. 3.Arrhenius acids are compounds that break up in water to give off _____________. 4.What color litmus paper would you use to test an acid? What color will it turn? 5. If your food tastes bitter, which do you think it could possibly be an acid or a base?

Practice Questions 6. A Br Ø nsted-Lowry base _________ hydrogen ions. 7. Phenolphthalein turns pink when it comes in contact with a(n) _________. 8. Which of the scientists defined the typical acid? 9. If you are eating and it has a sour taste, would that be an acid or a base? 10. If a piece of red litmus paper turns blue than it is a(n) ___________.

C. Strength Strong Acid/BaseStrong Acid/Base –Ionize completely in water –strong electrolyte - + HCl HNO 3 H 2 SO 4 HBr HI HClO 4 NaOH KOH Ca(OH) 2 Ba(OH) 2

C. Strength Weak Acid/BaseWeak Acid/Base –ionize partially in water –weak electrolyte - + HF CH 3 COOH H 3 PO 4 H 2 CO 3 HCN NH 3

C. Strength How strong or how weak an acid or base is depends on it’s degree of ionization

D. Finding the pH of Solutions Self- ionization of water – the simple dissociation of water H 2 O H + + OH - Concentration of each ion in pure water: [H + ] = 1.0 x M + [OH - ] = 1.0 x M Where K w = 1.0 x Ion-product constant for water (K w ), Where K w = 1.0 x K w = [H + ] [OH - ] Acid [H + ] > [OH - ] Base [H + ] < [OH - ] Neutral [H + ] = [OH - ]

[OH - ]pOHpH[H + ] 1 x x x x x x x x x Increasing acidity41 x x x x x x Neutral71 x x x x x x Increasing basicity101 x x x x x x x x x

Calculating [H+] and [OH-] reverse the pH equation The pH of a solution is Find the [H+] and [OH-] and determine whether it is acidic, basic, or neutral. –basic

Example 1. If the [H + ] in a solution is 1.0 x M, is the solution acidic, basic or neutral? 1.0 x M What is the concentration of the [OH - ]? Use the ion-product constant for water (K w ): K w = [H + ] [OH - ] 1.0 x = [1.0 x ] [OH - ] 1.0 x = [OH - ] 1.0 x x 10 -(14-5) pH 5 = acidic 1.0 x OH -

Examples 2. If the pH is 9, what is the concentration of the hydroxide ion? K w = [H + ] [OH - ] 1.0 x = [1.0 x ] [OH - ] 1.0 x = [OH - ] 3. If the pOH is 4, what is the concentration of the hydrogen ion? K w = [H + ] [OH - ] 1.0 x = [H + ] [1.0 x ] 1.0 x = [H + ] 14 = pH + pOH 14 = 9 + pOH 5 = pOH 14 = pH + pOH 14 = pH = pH

Example A solution has a pH of 4. Calculate the pOH, [H+] and [OH-]. Is it acidic, basic, or neutral? 14 = pH + pOH 14 = 4 + pOH 10 = pOH –acidic

Practice Problems: Classify each solution as acidic, basic or neutral. 1. [H + ] = 1.0 x [H + ] = [OH - ] = 1.0 x [OH - ] = 1.0 x Basic pH x acid pH 3 Neutral 14 – 4 = 10 base pH 10

Fill in the chart. [OH - ]pOHpH[H + ] 8 1x x × X X X X X X X X X

pH = -log[H + ] E. pH Scale 0 7 INCREASING ACIDITY NEUTRAL INCREASING BASICITY 14 pouvoir hydrogène (Fr.) “hydrogen power” pH is the negative logarithm of the hydrogen ion concentration

E. pH Scale pH = -log[H + ] pOH = -log[OH - ] pH + pOH = 14

E. The pH Scale

E. pH Scale pH of Common Substances

F. Neutralization Chemical reaction between an acid and a base. Products are a salt (ionic compound) and water.

F. Neutralization ACID + BASE  SALT + WATER HCl + NaOH  NaCl + H 2 O HC 2 H 3 O 2 + NaOH  NaC 2 H 3 O 2 + H 2 O –Salts can be neutral, acidic, or basic. –Neutralization does not mean pH = 7. weak strong neutral basic

G. Titration TitrationTitration –Analytical method in which a standard solution is used to determine the concentration of an unknown solution. standard solution unknown solution

Equivalence point (endpoint)Equivalence point (endpoint) –Point at which equal amounts of H + and OH - have been added. –Determined by… indicator color change G. Titration dramatic change in pH

G. Titration moles H + = moles OH - M  V  n = M  V  n M:Molarity V:volume n:# of H + ions in the acid or OH - ions in the base

G. Titration 42.5 mL of 1.3M KOH are required to neutralize 50.0 mL of H 2 SO 4. Find the molarity of H 2 SO 4. H3O+H3O+ M = ? V = 50.0 mL n = 2 OH - M = 1.3M V = 42.5 mL n = 1 MV# = MV# M(50.0mL)(2)=(1.3M)(42.5mL)(1) M = 0.55M H 2 SO 4

Naming Acids Binary acids –Contains 2 different elements: H and another –Always has “hydro-” prefix –Root of other element’s name –Ending “-ic” –Examples: HI, H 2 S, HBr, HCl

Naming Acids Ternary Acids - Oxyacids –Contains 3 different elements: H, O, and another –No prefix –Name of polyatomic ion –Ending “–ic” for “-ate” and “–ous” for “- ite” 3 –Examples: HClO 3, H 3 PO 4, HNO 2

Practice H 2 SO 3 –Sulfurous acid HF –Hydrofluoric acid H 2 Se –Hydroselenic acid Perchloric acid –HClO 4 Carbonic acid –H 2 CO 3 Hydrobromic acid –HBr

Definitions of Acids and Bases Arrhenius –Most specific/exclusive definition –Created by Svante Arrhenius, Swedish –Acid : compound that creates H + in an aqueous solution –Base : compound that creates OH - in an aqueous solution –HNO 3  H + + NO 3 - –NaOH  Na + + OH -

Definitions of Acids and Bases Bronsted-Lowry –A bit more general than Arrhenius definition –Most commonly used definition –Created by two scientists around the same time (1923) –Acid: Molecule or ion that is a proton (H + ) donor –Base: Molecule or ion that is a proton (H + ) acceptor –HCl + H 2 O  H 3 O + + Cl - –NH 3 + H 2 O ↔ NH OH -

Definitions of Acids and Bases Lewis –The most general definition –Defined by electrons and bonding instead of H + –Created by same scientist who electron-dot diagrams are named after –Acid: atom, ion, or molecule that accepts electron pair to form covalent bond –Base: atom, ion or molecule that donates and electron pair to form covalent bond –NH 3 + Ag +  [Ag(NH 3 ) 2 ] 1+ –BF 3 + F -  BF 4 -