Unit 10: Acids, Bases, Neutralization Reactions and pH.

Unit 10: Power Point Index Naming Acids…Slide 3 Acids, Bases and Neutralization Reactions …Slide 8 Calculation of pH…Slide 14 Strength of Acids and Bases …Slide 23

Naming Acids C.7.A name, acids using International Union of Pure and Applied Chemistry (IUPAC) nomenclature rules

Naming Acids without Oxygen Acids without Oxygen are named with the prefix “Hydro” and end in “-ic” Examples: HCl Hydrochloric Acid HF Hydrofluoric Acid HBr Hydrobromic Acid

Naming Acids with Oxygen For acids with oxygen in several forms, prefixes are used with the regular “-ic” and “-ous” endings. The “-ic” or regular ending for an acid comes from the polyatomic ion with the “-ate” ending. This gives the regular count for the oxygen for this type of acid. Example: H2SO4 SO4 is Sulfate so this acid is called Sulfuric Acid

Once you know the “-ic” ending, count the number of oxygens in the other forms to find the name of the acid. (REMEMBER: The regular “-ic” form comes from the polyatomic ion that ends with “-ate”) Two less oxygen Hypo ________ “-ous” Acid One less oxygen ________ “-ous” Acid Regular “-ic” form ________ “-ic” Acid One more oxygen Per ________ “-ic” Acid

The other names for the acids will come from the count based from the “regular acid name” H2SO4 “-ate” ending so it is Sulfuric Acid H2SO3 “-ite” ending so it is Sulfurous Acid H2SO2 two less oxygen will have a prefix and “-ous”ending. Hyposulfurous Acid. H2SO5 one more oxygen will have a prefix “Per” and the regular “-ic” ending. Persulfuric Acid

Acid Base Reactions C.10.G define acids and bases and distinguish between Arrhenius and Bronsted‐Lowry definitions and predict products in acid‐base reactions that form water C.10.H understand and differentiate among acid‐base reactions, precipitation reactions, and oxidation reduction reactions

Acids: General Information Acid: a substance which when added to water produces hydrogen ions [H+]. Properties: Acids: react with zinc, magnesium, or aluminum and form hydrogen gas (H2). react with compounds containing CO32- and form carbon dioxide and water. turn litmus red. taste sour (lemons contain citric acid, for example). DO NOT TASTE ACIDS IN THE LABORATORY!!

Bases Base: a substance which when added to water produces hydroxide ions [OH-]. Bases: feel soapy or slippery turn litmus blue they react with most cations to precipitate hydroxides taste bitter (ever get soap in your mouth?) DO NOT TASTE BASES IN THE LABORATORY!!

Arrhenius Model Basis for the model--action in water acid definition: produces H+ in water solution base definition: produces OH- in water solution

Bronsted-Lowry Model Basis for the model-- proton transfer acid definition: donates a proton base definition: accepts a proton conjugate acid definition: the acid becomes the conjugate base after it donates the proton because it can now accept it back. conjugate base definition: the base becomes the conjugate acid after it accepts the proton because it can now donate it back.

Acid-Base Reactions Strong acid + strong base: HCl + NaOH → NaCl + H2O net ionic reaction:  H+ + OH-  →   H2O Strong acid + weak base: example:  write the net ionic equation for the reaction between hydrochloric acid, HCl, and aqueous ammonia, NH3. · Strong base + weak acid: example:  write the net ionic equation for the reaction between citric acid (H3C6H507) and sodium hydroxide. NH3(aq) + HCl(aq) --> NH4Cl(aq) ; NH3 + H + Cl --> NH4 + Cl ; So that ends up being NH3 + H+ --> NH4 3NaOH + H3C6H5O7--------->Na3C6H5O7 + 3H2O ; 3OH- + 3H+ --> 3H20 ; OH- + H+ --> H20

Calculation Of pH C.10.I define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution

Water Dissociation: Water dissociation: H2O(l) → H+(aq) + OH-(aq) equilibrium constant, KW = [H+][OH-] / [H2O] Note:  water is not involved in the equilibrium expression because it is a pure liquid, also, the amount of water not dissociated is so large compared to that dissociated that we consider it a constant Value for Kw = [H+][OH-] = 1.0 x 10-14 [H+] for pure water = 1 x 10-7 [OH-] for pure water = 1 x 10-7 Note: The reverse reaction, H+(aq) + OH-(aq)  →   H2O(l) is not equal to 1 x 10-14

Definitions of acidic, basic, and neutral solutions based on [H+] acidic: if [H+] is greater than 1 x 10-7 M basic: if [H+] is less than 1 x 10-7 M neutral: if [H+] if equal to 1 x 10-7 M

Example 1: What is the [H+] of a sample of lake water with [OH-] of 4.0 x 10-9 M? Is the lake acidic, basic, or neutral? Solution: [H+] = 1 x 10-14 / 4 x 10-9 = 2.5 x 10-6 M Therefore the lake is slightly acidic Remember: the smaller the negative exponent, the larger the number is. Therefore: acid solutions have exponents of [H+] from 0 to -6. basic solutions have exponents of [H+] from -8 to -14.

Example 2: What is the [H+] of human saliva if its [OH-] is 4 x 10-8 M? Is human saliva acidic, basic, or neutral? Solution: [H+] = 1.0 x 10-14 / 4 x 10-8 = 2.5 x 10-7 M The saliva is pretty neutral.

pH relationship between [H+] and pH pH = -log10[H+] Definition of acidic, basic, and neutral solutions based on pH acidic: if pH is less than 7 basic: if pH is greater than 7 neutral: if pH is equal to 7

The [H+] can be calculated from the pH by taking the antilog of the negative pH or 10-pH. Example 3:  calculate the [OH-] of a solution of baking soda with a pH of 8.5. Solution:  First calculate the [H+] at pH 8.5, the antilog of -8.5 (or 10-8.5) is 3.2 x 10-9. Thus the [H+] is 3.2 x 10-9 M Next calculate the [OH-] 1.0 x 10-14 / 3.2 x 10-9 = 3.1 x 10-6 M

Example 4:  Calculate the pH of a solution of household ammonia whose [OH-] is 7.93 x 10-3 M. Solution:  This time you first calculate the [H+] from the [OH-] 7.93 x 10-3 M OH- = 1.26 x 10-12 M H+ Then find the pH -log[1.26 x 10-12] = 11.9

Now you try a few by yourself. Practice #1. What is the pH of a solution of NaOH that has a [OH-] of 3.5 x 10-3 M? Practice #2. The H+ of vinegar that has a pH of 3.2 is what? Practice #3. What is the pH of a 0.001 M HCl solution? #1 pH = 11.5 #2 [H+] = 6.3 x 10-4 #3 pH = 3

Strength of Acids and Bases C.10.J distinguish between degrees of dissociation for strong and weak acids and bases

Strong Acids: completely dissociate in water, forming H+ and an anion. example: HNO3 dissociates completely in water to form H+ and N031-. The reaction is HNO3  →   H+ + NO31- A 0.01 M solution of nitric acid contains 0.01 M of H+ and 0.01 M NO3- ions and almost no HNO3 molecules. The pH of the solution would be 2.0.

There are only 6 strong acids: You must learn them There are only 6 strong acids: You must learn them. The remainder of the acids therefore are considered weak acids. HCl H2SO4 HNO3 HClO4 HBr HI

Note: when a strong acid dissociates only one H+ ion is removed Note: when a strong acid dissociates only one H+ ion is removed. H2SO4 dissociates giving H+ and HSO4- ions. H2SO4  →   H+ + HSO41- A 0.01 M solution of sulfuric acid would contain 0.01 M H+ and 0.01 M HSO41- (bisulfate or hydrogen sulfate ion)

Weak acids: a weak acid only partially dissociates in water to give H+ and the anion for example, HF dissociates in water to give H+ and F-. It is a weak acid. with a dissociation equation that is HF  ↔   H+ + F- Note the use of the double arrow with the weak acid. That is because an equilibrium exists between the dissociated ions and the undissociated molecule. In the case of a strong acid dissociating, only one arrow (  →  ) is required since the reaction goes virtually to completion. An equilibrium expression can be written for this system: Ka = [ H+][F-] / [HF]

Which are the weak acids Which are the weak acids?   Anything that dissociates in water to produce H+ and is not one of the 6 strong acids. Molecules containing an ionizable proton. (If the formula starts with H then it is a prime candidate for being an acid.) Also: organic acids have at least one carboxyl group, -COOH, with the H being ionizable. Anions that contain an ionizable proton. HSO41-  →   H+ + SO42- Cations:  (transition metal cations and heavy metal cations with high charge) also NH4+ dissociates into NH3 + H+

Strong Bases: They dissociate 100% into the cation and OH- (hydroxide ion). example:  NaOH  →   Na+ + OH- a. 0.010 M NaOH solution will contain 0.010 M OH- ions (as well as 0.010 M Na+ ions) and have a pH of 12. Which are the strong bases? The hydroxides of Groups I and II.

Note: the hydroxides of Group II metals produce 2 mol of OH- ions for every mole of base that dissociates. These hydroxides are not very soluble, but what amount that does dissolve completely dissociates into ions. exampIe: Ba(OH)2  →   Ba2+ + 2OH- a. 0.000100 M Ba(OH)2 solution will be 0.000200 M in OH- ions (as well as 0.00100 M in Ba2+ ions) and will have a pH of 10.3.

Weak Bases: What compounds are considered to be weak bases? Most weak bases are anions of weak acids. Weak bases do not furnish OH- ions by dissociation. They react with water to furnish the OH- ions. Note that like weak acids, this reaction is shown to be at equilibrium, unlike the dissociation of a strong base which is shown to go to completion.

When a weak base reacts with water the OH- comes from the water and the remaining H+ attaches itself to the weak base, giving a weak acid as one of the products. You may think of it as a two-step reaction similar to the hydrolysis of water by cations to give acid solutions. examples: NH3 + H2O  →   NH4+ + OH- methylamine: CH3NH2+ H2O  →   CH3NH3+ + OH- acetate ion: C2H3O2- + H2O  →  HC2H3O2 + OH- General reaction: weak base + H2O → weak acid + OH- Since the reaction does not go to completion relatively few OH- ions are formed.