Acids and Bases

Acids and Bases Definitions Demo – Intro to Acids and Bases What is an indicator? Universal indicator changes from green to _____ in the presence of acid. Universal indicator changes from green to _____ in the presence of base. What do acids and bases make when they neutralize each other? __________ & __________ Chemical that changes color for an acid or base RED BLUE Salt Water

Acids and Bases Definitions Review Naming Acids and Bases from formula H2CO3 ________________ Ca(OH)2 ________________ H3N ________________ HC2H3O2 ________________ Review Writing formulas from names: Hydrofluoric acid ________ Copper (II) hydroxide ________ Magnesium hydroxide ________ d. Sulfurous acid ________ e. Phosphoric acid ________ Carbonic Acid Calcium Hydroxide Hydronitric Acid Acetic Acid HF Cu(OH)2 Mg(OH)2 H2SO3 H3PO4

Arrhenius Model of Acids and Bases What are acids and bases? Arrhenius model (1887) Acid – Contains H+ and produces H+ in solution Base – Contains OH- and produces OH- in solution Ex: HCl(g)  H+(aq) + Cl –(aq)   Ex: NaOH(s)  Na+(aq) + OH-(aq) ** What was the problem with Arrhenius’s model? Ex. NH3 + H2O  NH4+ + OH- Ammonia (base) __________________________________________ H+ Cl- Cl- H+ Acids and bases both dissociate into ions when dissolved in water Na+ OH- OH- Na+ Arrhenius didn’t include all bases

Bronstead Lowry Model of Acids and Bases Bronsted-Lowry Model (includes ALL Bases – based on how acids and bases act) Acid – Donates H+ Base – Accepts H+ HX(aq) + H2O(l)   H3O+(aq) + X-(aq) Ex: HF + H2O   H3O+ + F – Ex. NH3(aq) + H2O(l)   NH4+(aq) + OH-(aq) Look at the products! A B A B B A

Summary Are all Arrhenius acids also Bronsted-Lowry acids? ___ Why? __________________ Are all Bronsted-Lowry acids also Arrhenius acids? ____ Are all Arrhenius bases also Bronstead-Lowry bases? __ Why? ___________________ Are all Bronstead-Lowry bases also Arrhenius bases? ____ Why? _______________________________ Yes Donates H+ Yes Contains H+ Yes Accepts H+ No Some don’t contain OH- (like NH3)

Stations Notes Characteristics Acids Bases Blue Litmus - b. c. Taste   Reaction with metals Conductivity Texture More H+ or OH- ? pH range Indicators: a. Litmus paper b. Phenolphthalein (base indicator) c. Universal Indicator  a.Red Litmus – Blue Litmus - b. c. Examples - Acids and bases are common in both the laboratory and the home: Laboratory: Home:

Stations Notes Characteristics Acids Bases Blue Litmus - Turns Red Taste  Sour Bitter Reaction with metals Yes No Conductivity  Yes Texture Like Water Slippery More H+ or OH- ? More H+ More OH- pH range Less than 7  More than 7 Indicators: a. Litmus paper b. Phenolphthalein (base indicator) c. Universal Indicator  a.Red Litmus – Stays Red Blue Litmus - Turns Red b. No change c. Red    a.Red Litmus – Turns Blue Blue Litmus – Stays Blue b. Turns hot pink c. Blue Examples - Acids and bases are common in both the laboratory and the home: Laboratory: Home:

Acid-Base Reactions

DEMO: MOM Rainbow DEMO (MOM rainbow) – Neutralization reaction of an Antacid. When do we take antacids? How do antacids work in your stomach? What is the formula of Milk of Magnesia? What type of substance is an antacid? ________How do you know? Give another example of an antacid. Why is it called “antacid”? What is the scientific name for stomach acid? What is the formula?   Write the equation for magnesium hydroxide (antacid) neutralizing a stomach acid. Predict and name the products. Balance the equation: _________ + ________ _________ + ________ Acid Reflux They neutralize the stomach acid Mg(OH)2 Base It can neutralize the acid It is anti – acid, does the opposite Hydrochliric Acid HCl HCl Mg(OH)2 MgCl2 H2O Product Names: Magnesium Chloride and Water

Salt - Ionic compound made up a cation from a metal and an anion from an non-metal What type of reaction is acid-base neutralization? Double Replacement Reaction

Acid Base Neutralization Reaction An acid base neutralization reaction is a double replacement reaction that results in a salt and water (pH = 7) Ex: Hydrochloric acid is neutralized by calcium hydroxide. HCl + Ca(OH)2  ________ + _________ CaCl2 H2O Product Names: Calcium Chloride and Water Now its time for you to work on the practice! Use your notes to help you answer the questions!

pH Scale

pH Scale Tenfold Potential of Hydrogen [H+] = [OH-] neutral (pH = 7) Molarity (M) [H+] represents the molar concentration {____________} of the hydrogen ions. [H+] 1x 100M 1 x 10-14M pH scale: 0 7 14 **A change of one pH unit represents a ____________change in ion concentration. What does pH stand for? ______________________  A pH of 4 is ___________________ than a pH of 5 A pH of 10 is _________________________ than a pH of 5 Tenfold Potential of Hydrogen [H+] = [OH-] neutral (pH = 7) [H+] < [OH-] base (pH above 7) [H+] > [OH-] acid (pH below 7) 10 times stronger 100,000 times weaker

To find pH if you know the Hydrogen ion concentration, use the following formula: pH = -log[ H+ ] Calculate the pH of each solution: Solution 1 has a [H+] equal to 1x10-7M Solution 2 has a [H+] equal to 3.6 x 10-9M pH = 7 pH = -log(1E-7) Answer: ________________ Is the solution an Acid , Base , or Neutral ? pH = -log(3.6E-9) pH = 8.44 Answer: ________________ Is the solution an Acid , Base , or Neutral ?

To find the H+ concentration when given the pH use: [H+] = 2nd log (-pH) Calculate the [H+] (concentration) for each solution. Solution 1 has a pH of 4.0 Solution 2 has a pH of 11.5 1 x 10-4 M Answer: ________________ [H+] = 2nd log (-4) Is the solution an Acid , Base , or Neutral ? 3.16 x 10-12 M Answer: ________________ [H+] = 2nd log (-11.5) Is the solution an Acid , Base , or Neutral ?

To find hydroxide concentration (or the [H+] if not given the pH) To find hydroxide concentration (or the [H+] if not given the pH). Use the following formula: Kw = [H+][OH-] = 1 x 10-14 At 298K, the [OH-] is 1.0 x 10-11M. Find the [H+] in the solution and determine whether the solution is acidic, basic, or neutral. Formula: Work: Answer: __________________ Kw = [H+][OH-] 1E-14 = [H+](1E-11) .001 M or 1 x 10-3 M Is the solution an Acid , Base , or Neutral ?

To find pH if you know the hydroxide ion concentration To find pH if you know the hydroxide ion concentration. Use the following formulas: Kw = [H+][OH-] = 1 x 10-14 & pH = -log[ H+ ] At 298K, the [OH-] is 1.0 x 10-10M. Find the pH of the solution and determine whether the solution is acidic, basic, or neutral. Formulas: Work: Answer: _______ Kw = [H+][OH-] = 1 x 10-14 & pH = -log[ H+ ] 1 x 10-14 = [H+](1E-10) [H+] = pH = -log [ H+ ] pH = -log( ) 1E-4 M 1E-4 M pH = 4 Is the solution an Acid , Base , or Neutral ?

Strengths of Acids and Bases Weak Strong

Acid Strength Acids that dissociate into ions (ionize) completely in aqueous solutions are called _________ acids; produce the __________ number of ions, so they are______conductors of electricity and therefore strong acids are _______ electrolytes. Examples: HCl, HNO3, HI, H2SO4   Acids that ___________ ionize in aqueous solutions are called ________ acids; cannot conduct electricity as efficiently and therefore, weak acids are ______ electrolytes. Examples: HC2H3O2, HF, HCN, H2CO3 STRONG maximum good STRONG partially WEAK WEAK

Base Strength completely 1. Bases that ionize ____________in aqueous solutions into metal ions and __________ ions are called _________ bases. Base must contain _____ to be a strong base. Examples: NaOH, KOH, RbOH, CsOH, Ca(OH)2 2. Bases that ____________ ionize in solutions are called ________ bases. Examples: NH3, CH3NH2 (methylamine) hydroxide STRONG OH- partially WEAK

Summary 100 Strong acids and bases dissociate ____% into ions in solution. Weak acids and bases dissociate about __% into ions in solution. 1

Difference between Strength and Concentration Concentration (dilute or concentrated) refers to the ____________of the acid or base molecules dissolved in a volume of solution (molarity = M). Strength (weak or strong) refers to the degree of ____________, which means how easily the acid or base separates into _____. Example: 0.6 M HCl or 6 M HC2H3O2   Which more concentrated?______ Which is stronger? _________ Which acid has a higher pH?_____ How do you know? Which acid has a lower pH? ________ How do you know? amount dissociation ions HC2H3O2 HC2H3O2 HCl Strong Acid HC2H3O2 Weak Acid

The degrees of dissociation into ions for HCl and HC2H3O2 1% dissociation (ionization) Both, HC2O3H2 molecules & ions are in a solution. Molecules > Ions 100% dissociation (ionization) No HCl molecules, just ions Molecules < Ions