Chapter 14: Acids and Bases and pH

Acids are proton donors (give a hydrogen away) 1) Sour taste 2) Litmus paper (common indicator) changes from blue to red in an acid or red litmus paper stays red. 3) Acids always contain hydrogen. Acids are proton donors (give a hydrogen away) Bronsted-Lowry definition of an acid 4) Acids react with metals to form hydrogen gas and a metal compound called corrosion

HCl(g) + H2O (l) ----- H3O+ (aq) + Cl- (aq) Acids – produce hydronium ions in water. HCl(g) + H2O (l) ----- H3O+ (aq) + Cl- (aq) Also known as Arrhenius Acids When a hydrogen atom is attached to a water molecule. Hydronium ion: H3O+ ion is positively charged. Conduct an electrical current (charged particles). Hydrogen is always written first in an acid. If there is Only one hydrogen – HCl – monoprotic Diprotic (2) and polyprotic (more than 2) Example: H2SO4 – sulfuric acid - diprotic

Note: if hydrogen is not written first – not an acid! BUT not all hydrogen containing compounds are acids. Example: sugar C11H22 O11 Note: if hydrogen is not written first – not an acid!

Bases 1) taste bitter, feel slippery 2) turn litmus paper from red to blue or blue paper stays blue. 3) emulsify (dissolve) fats and oils Arrhenius bases produce hydroxide ion (OH-) when dissolved in water. (need to know name and symbol) 5) Bases are called proton acceptors Proton acceptors- Bronsted – Lowry definition of a base

NaOH (s) ------- Na+ (aq) + OH- (aq) OH- hydroxide ion Common Base - Sodium Hydroxide (NaOH) also known as ‘lye’ common base – very strong. NaOH (s) ------- Na+ (aq) + OH- (aq) OH- hydroxide ion Example: NH3 (g) + H2O (l) --- NH4+ (aq) + OH- (aq) Ammonia – covalent base Water does play a role in this reaction Since NH3 accepts a proton (H+) and is now NH4+ it is considered a base. H2O

14.2 Strengths of Acids and Bases Strong Acids and Bases Completely ionize in water

Common acids – know these Strong: H2SO4 – sulfuric acid HNO3 – nitric acid HCl – hydrochloric acid – highest production of any acid in the United States. Used in the production of paper, fertilizers, petroleum refining and car batteries. used in the production of rubber, plastics, pharmaceuticals, fertilizers and explosives used in the pickling of steel, used to purify magnesium from sea water, correct swimming pool pH, found in your gastric juices (aids in the digestion of proteins) Sold commerically as “Muriatic Acid”

Strong acids : ionize well in water (lose hydrogen quickly) = good electrolytes

Weak acids: HC2H3O2 – acetic acid (acid in vinegar) know this one H2CO3 – carbonic acid (used for carbonating soda) H3PO4 – phosphoric acid (a flavoring agent in soda) H3BO3 – boric acid (eye wash) Weak acids do not ionize well in solution (produce only a few H+ in solution) Poor Electrolytes! Acetic acid

Common Bases – Strong bases ionizes completely in water, produce large # of ions therefore Good Electrolytes. Strong Bases: KOH – battery electrolyte NaOH – used for making soap, Drano; know this one Ca(OH)2 – leather production, making plaster Mg(OH)2 – laxative, antacid

Weak Bases: do not produce large amount of ions, weak electrolytes. NH4OH – ammonium hydroxide (household cleaner) Al(OH)3 – aluminum hydroxide (antacid, deodorant) NH3 Ammonia – household cleaning products know this one

pH scale is used to measure the acidity of solution. Definition: The pH (‘potential of hydrogen’) is a measure of hydronium ion (H3O+)concentration. It is a Mathematical scale 0-14. Logarithmic Scale – based on powers of 10. Example: pH of 3 is 10 times more acidic than a pH 4. pH of 3 is 100 (10 x 10) times more acidic than the pH of 5.

7 = neutral (distilled water) pH less than 7 = acidic pH above 7 = basic 7 = neutral (distilled water) To calculate pH scale = take the negative of the exponent of the hydronium ion concentration = -log [H3O+] Concentrations of hydronium and hydroxide in water: [H3O+] x [OH-] = 1 x 10 -14 Example: If concentration of the hydronium ion [H3O+] is 10-8 M. Then the solution has a pH of 8. Example: If the hydroxide ion [OH-] concentration is 10-5 M, then the pH = 10 -14 /10 -5 = 10 -9 -- pH of 9.

pH of common materials showing the relationship between pH and the hydronium ion concentration. Pure water has a pH of 7.0. show demo Normal rain is slightly acidic because carbon dioxide (CO2) dissolves into it forming weak carbonic acid, giving the resulting mixture a pH of approximately 5.6 at typical atmospheric concentrations of CO2. As of 2000, the most acidic rain falling in the U.S. has a pH of about 4.3.

Neutral Solution: [H3O+] = [OH-] Acid Solution: [H3O+] > [OH-] http://www.explorelearning.com/index.cfm?method=cResource.dspResourcesForCourse&CourseID=309 Gizmo - pH Neutral Solution: [H3O+] = [OH-] Acid Solution: [H3O+] > [OH-]

15.1 Acid and Base Reactions The reaction between an acid and a base is called a Neutralization Reaction. Usually neutralization reactions produce water and a salt. NaOH (aq) + HCl (aq) ----- NaCl (aq) + H2O (l) pH = 7

Salt – Ionic compound formed from the negative part of the acid and the positive part of the base. Neutral substance. NaCl is not the only ionic compounds that are salts. Others include: KCl, KBr, NH4NO3

Indicators are used to test whether a substance is an acid or a base. Phenolphthalein – common indicator, colorless in an acid; pink in a base. pink in a base. colorless in an acid