Unit 8: Acids and Bases Who is Arrhenius?

Arrhenius Acids Svante Arrhenius: scientist who proposed a theory to explain the properties of acids and bases Arrhenius Acid: any substance that gives up a hydrogen ion (H+ or proton) in solution

Characteristic of Acids To be an acid, it must be dissolved in water (aq) When acids dissolve in water, they break apart to form FREELY MOVING IONS. Ionization: when a covalent compound breaks into ions in water due to the high polarity (ex) HCl Dissociation: when an ionic compound breaks into ions in water (ex) HNO3 Any compound that dissolves in water to form ions will conduct electricity or is called an electrolyte.

Characteristic of Acids Acids react with metals (those above H2 on Table J) to produce hyrodgen gas (single replacement reaction) (ex) Mg(s) + 2HCl (aq)  MgCl2 (aq) + H2 (g) (ex) Al (s) + 2 HBr (aq)  Acids taste sour like citric acid and vinegar

Practice with Particle Diagrams Identify the acids in the following reactions: (ex) HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) Reason: HCl is the acid because it gives up a H+ (ex) H2CO3(g) + H2O(l)  H3O+(aq) + (HCO3)-1(aq) H2CO3 is the acid because it gives up a H+ (ex) HF(g) + H2O(l)  H3O+(aq) + F-(aq) HF is the acid because it gives up a H+ H2SO4 is a diprotic acid: this means that when it completely dissociates it produces twice as much H+.

Strong Acids What product is always present when acid is mixed with water? Strong Acids: These are acids that completely ionize or dissociate into ions in water. HNO3, H2SO4, HClO4, HCl, HBr, HI Weak Acids: These acids do not completely break into ions in water. SOME of the acid stays together in compound form All other acids Organic acids: are weak acids that end in –COOH (ex) CH3CH2COOH H3O+ or hydronium (aka a hydrated H+) It is the final H that ionizes in water

Strong Acids Any strong acid is also a strong electrolyte because it means that there are more ions in solution to conduct electricity. Strong Acid Weak Acid HNO3 HC2H3O2

Arrhenius Bases Arrhenius Base: any substance that gives up a hydroxide ion (OH)- in solution Characteristics of Bases: To be a base, it must be dissolved in water (aq) All bases are ionic and therefore dissociate in water to form FREELY MOVING IONS.

Characteristics of Bases Bases are electrolytes. Solutions of bases feel slippery like soap and cleaners. Bases taste bitter like soap and cleaners. Identify the bases in the following reactions: (ex) NaOH(s) + H2O(l)  Na+(aq) + OH-(aq) Reason: NaOH because it forms OH- when with water (ex) Ca(OH)2(s) + H2O(l)  Ca+2(aq) + 2OH-(aq) Ca(OH)2 because it forms OH- when with water **(ex) NH3(g) + H2O(l)  NH4+(aq) + OH-(aq) NH3 because it forms OH- when with water

Strong Bases Strong Bases: those bases that completely dissociate in water. Bases formed from group 1 and 2 metals. (LiOH, NaOH, Mg(OH)2) Weak Bases: those bases that do not completely break up in water. all other metals bonded to (OH)- (Al(OH)3, NH4OH)

Naming Acids Binary Acids: Name the hydrogen in the acid hydro- Name the anion and change the ending of the name to –ic acid (ex) HCl(aq) (ex) HI (aq) (ex) HBr (aq) (ex) H2S (aq) Hydrochloric acid Hydroiodic acid Hydrobromic acid Hydrosulfuric acid

Naming Acids Ternary Acids (with PAI’s): Go to Table E and name the PAI DO NOT use the prefix hydro- If the PAI ends in -ate it changes to -ic acid -ite it changes to -ous acid (ex) H2CO3(aq) (ex) H3PO4(aq) (ex) H2SO4(aq) (ex) H2SO3(aq) Carbonic acid  Phosphoric acid Sulfuric acid   Sulfurous acid

Naming Bases Bases: bases are all ionic compounds therefore they are named just like ionic compounds. Name 1st element Use roman numeral if the metal has more than one charge listed 2nd half of the name will always be hydroxide. (ex) NaOH(aq) (ex) Ca(OH)2(aq) (ex) Fe(OH)3(aq) Sodium hydroxide Calcium hydroxide Iron (III) hydroxide

Indicators Indicator: a substance that changes color if its in an acid or a base ** Most commonly used indicators: Acid Base Litmus Phenolphthalein (phth) Universal indicator Table M Red Blue Clear Pink BIV ROY G

pH and Indicators pH scale: Methyl orange Bromthymol blue (btb) Phth 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Litmus Bromcresol green Thymol blue red yellow red blue yellow blue yellow blue colorless pink yellow blue

pH pH: a value used to describe the acidity or alkalinity of an (aq) solution by indicating the [H+] ions. If the [H+] ions goes up, pH goes down pH = -log [H+] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acid [H+]>[OH-] Base [H+]<[OH-] Neutral [H+]=[OH-]

pH and Molarity pH and Molarity: For strong acids and bases you can convert the exponent of the [ ] directly into pH (n) if the [ ] is 1x 10-n. pH [H+] in Molarity [H+] in decimal 5 4 3 2 1 pH [H+] in Molarity [H+] in decimal 5 4 3 2 1 0.00001 1 x 10-5 1 x 10-4 0.0001 1 x 10-3 0.001 Increasing acidity 1 x 10-2 0.01 1 x 10-1 0.1

pH and Molarity cont’d (ex) Calculate the pH of a .0001 M HCl (aq) solution. Is this an acid or base? (ex) Calculate the pH of a solution whose concentration of H+ is 1 x 10-10. (ex) Calculate the pH of a solution whose concentration of H+ is 1 x 10-1.

pOH pOH: a value used to describe the acidity or alkalinity of an (aq) solution by indicating the [OH-] ions. If the [OH-] ions goes up, pOH goes down pOH = -log [OH-] 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Acid [H+]>[OH-] Base [H+]<[OH-] Neutral [H+]=[OH-]

pOH and Molarity pOH and Molarity: For strong acids and bases you can convert the exponent of the [ ] directly into pOH (n) if the [ ] is 1x 10-n. pOH [OH-] in Molarity [OH-] in decimal 5 4 3 2 1 0.00001 1 x 10-5 1 x 10-4 0.0001 1 x 10-3 0.001 Increasingly basic 1 x 10-2 0.01 1 x 10-1 0.1

pOH and Molarity cont’d (ex) Calculate the pOH of a .0001 M NaOH (aq) solution. Is this an acid or a base? (ex) Calculate the pOH of a solution whose concentration of OH- is 1 x 10-10. (ex) Calculate the pOH of a solution whose concentration of OH- is 1 x 10-1.

pH and pOH 14 11 7  pH + pOH always equals____________ (ex) If the pH of a solution is 3, the pOH is ________________. (ex) If the pOH of a solution is 7, the pH is ________________. 11 7 [H+] pH [OH-] pOH Acid, base or neutral? 0.0001 M neutral 1.0 x 10-3 M 8 9 4 1.0 x 10-10 M 10 acid 1.0 x 10-7 M 7 1.0 x 10-7 M 7 1.0 x 10-11 M 11 3 base 1.0 x 10-6 M 6 1.0 x 10-8 M acid 1.0 x 10-9 M 1.0 x 10-5 M 5 base

Diprotic acids/dihydroxy bases and [ ] (ex) Calculate the pH of a 0.0005 M H2SO4 (aq) solution. (ex) How many times more concentrated is a pH of 2 compared to a pH of 4?

Kw: Ionization Constant for Water Water is a substance that is very polar. This means that water will ionize if the collisions between the water molecules have enough energy and the right orientation. Water molecule + Water molecule  Hydroxide ion + Hydronium ion 3D Model: -1 +1 

Kw cont’d  Water self ionizes. It does not need to be dissolved in anything else.  The ionization of pure water occurs to a very small extent (it means it doesn’t happen very much). We can write a Kw expression to show how much water actually breaks apart  this is called the ionization constant for water. At STP, Kw =  We can use the Kw to calculate the [H+] or [OH-]. [H+][OH-] = 1 x 10 -14

Kw cont’d  Therefore, in pure water at 273K, the [H3O+] and [OH-] are each 1 x 10-7 M. **this is because pure water is neutral, therefore [H3O+]=[OH-].  Remember, Kw means that there is an equilibrium. That means if the [ ] of one thing changes, everything else also changes. ** As [H3O+] goes up, [OH-] goes down.

Bronsted-Lowry Theory This theory DOES NOT replace the Arrhenius theory, it only broadens it to include more substances as bases. THE DEFINITION OF AN ACID IS EXACTLY THE SAME!! For example, NH3 (aq) and Na2CO3 (aq) are two compounds that act like bases, however they do not contain OH- ions. Instead they steal a H+ from water to FORM an OH-.

B-L cont’d **With Bronsted and Lowry it’s all about the H+ (proton). And we always look at the reverse reaction as well. B-L Acid: B-L Base: (ex) HCl (aq) + H2O  H3O+ (aq) + Cl- (aq) (ex) NH3 (aq) + H2O  NH4+ (aq) + OH- (aq) Conjugate Acid/Base Pair: two substances that relate to each other by the gain/loss of a proton (ex) NH3 / NH4+ (ex) Cl- / HCl Any substance that donates an H+ Any substance that accepts (steals) an H+

Conjugate Acids and Bases the particle formed when a base gains an H+ ion. Conjugate Base: the particle formed when an acid loses an H+ ion. Conjugate acid = H+ + Conjugate base  An acid on the reactant side becomes a conjugate base on the product side.  A base on the reactant side becomes a conjugate acid on the product side.  An acid and its conjugate base are always on opposite sides of the reaction.  A base and its conjugate acid are always on opposite sides of the reaction.

B-L Practice Acids Bases (ex) NH3 (aq) + H2O  NH4+ (aq) + OH- (aq) (ex) HNO2 (aq) + H2O  H3O+ (aq) + NO2- (aq) (ex) HS- (aq) + NH3 (aq)  NH4+ (aq) + S-2 (aq)

Acid/Base Neutralization When equal molar quantities of an acid and a base are mixed, a neutral sol’n is produced. *For every 1 mole of OH- ions there needs to be 1 mole of H+ ions. Products from mixing an acid and a base are always water and a salt. Salt: any ionic cmpd that is NOT an acid or base The products of a strong acid and strong base neutralization always have a pH of 7 and [OH-] and [H+] are equal.

Practice with Neutralization **Neutralization rxns are double replacement rxns. If the reactants are equal molar quantities of a strong acid and a strong base  If the reactants are equal molar quantities of a strong acid and a weak base  If the reactants are equal molar quantities of a weak acid and a strong base  (ex) HCl (aq) + NaOH (aq)  pH (ex) CH3COOH (aq) + NaOH (aq)  (ex) HNO3 (aq) + KOH (aq)  (ex) HCl (aq) + Al(OH)3 (aq)  pH = 7 pH < 7 pH > 7

Acid/Base Titrations Titration: a method used in the lab to determine the [ ] of an unknown acid or base by neutralizing. A solution of known [ ] (standard sol’n) is added to a solution of unknown [ ] until it is completely neutral. The point at which neutralization occurs is called the endpoint. The endpoint can be found by adding an indicator to the unknown.

Titrations Titration Equation: Look on Table _____ MAVA = MBVB T moles H+ = moles OH- T

Titration Practice (ex) What volume of 2.0M HNO3 is needed to neutralize 40. mL of 5.0M NaOH? (ex) You need 20 mL of 2M HCl, however the stock solution is 12M. How many mL of the stock solution do you need to make your final solution? (ex) There is 3 moles of HBr in a solution. How many mL of 2.5 M NaOH need to be added to neutralize the solution?