Topic 10 Acids, Bases & Salts

Topic 10-Acids, Bases and Salts (ABS) Properties of Acids and Bases Definitions of Acids and Bases a. Arrhenius b. Bronsted-Lowry c. Lewis Strength of Acids and Bases Naming Acids and Bases Reactions with Acids and Bases a. Acids with Metals b. Neutralization I. Strong acid + strong base II. Strong acid + weak base III. Weak acid + strong base IV. Weak acid + weak base c. Titration pH Acid/Base Indicators

Properties of Acids & Bases Donate H+ ion (H3O+ ion) in water React with most metals to produce H2 gas Affect colors of indicators Neutralize bases Sour taste Electrolyte Donate OH- ion in water Affect colors of indicators Neutralize acids Bitter taste Slippery Electrolyte

Tables K & L list some common acids and bases

Definitions of Acids and Bases There are three different definitions of acids/bases 1. Arrhenius (1884) Acids- Are hydrogen containing compounds that ionize to yield hydrogen (H+) ions (also known as hydronium ions (H3O+) in aqueous solutions Bases- are compounds that ionize to yield hydroxide (OH-) ions in aqueous solutions Svante Arrhenius 1859-1927

2. Bronsted-Lowry (1923) Acids- An acid is a hydrogen-ion donor Bases- A base is a hydrogen-ion acceptor NH3(aq) + H2O(l) = NH4+(aq) + OH-(aq) B A A B Johannes Nicolaus Bronsted 1879-1947 Thomas Martin Lowry 1874-1936

3. Lewis (1923) Acids- accept a pair of electrons during a reaction Bases- donate a pair of electrons during a reaction Gilbert N. Lewis 1875-1946

There are five strong acids They are considered strong because they ionize 100% You must memorize the five strong acids HCl HBr HI HNO3 H2SO4

Strong Bases A strong base must be a metal from Group 1 or Group 2 + OH Gp. 1- LiOH, NaOH, KOH, RbOH, CsOH, FrOH Gp. 2- Be(OH)2, Mg(OH)2, Ca(OH)2, Sr(OH)2, Ba(OH)2, Ra(OH)2 If the metal is from any other group, it is a weak base *Be careful…bases MUST be a metal + OH Don’t be fooled…if there is a nonmetal + OH it is an alcohol Ex.: C2H5OH C & H are nonmetals so this is NOT a base but is an alcohol

Naming Acids Binary Acids Made up of H + NM Name starts with hydro Change the ending of the NM to ic and add the word acid Ex: HCl Hydro + Chloric acid Hydrochloric acid Ternary Acids Made up of H + PAI Does not start with word hydro If PAI ends in ate-change it to ic and end with acid If PAI ends in ite-change it to ous and end with acid Ex: H2SO4 SO4 = sulfate So it becomes sulfuric acid

Lets try some: HClO- Hypochlorous acid HF- Hydrofluoric acid HClO2- Chlorous acid H2S- Hydrosulfuric acid HClO3- Chloric acid HNO2- Nitrous acid HClO4- Perchloric acid HNO3- Nitric acid HC2H3O2- Acetic acid HMnO4- Permanganic acid H3P- Hydrophosphoric acid H3PO4- Phosphoric acid

Reactions with Acids 1. Reaction with most metals to produce hydrogen gas These are just single replacement reactions Zn + HCl  H2 + ZnCl2 Mg + H2SO4  H2 + MgSO4 Cu + H2S  no reaction

2. Neutralization A very specific double replacement reaction Acid + base  salt + water HCl + NaOH  NaCl + H2O H2SO4 + Mg(OH)2  MgSO4 + H2O HC2H3O2 + Ni(OH)3  Ni(C2H3O2)3 + H2O

Hydrolysis of a Salt Four scenarios 1. Strong acid + strong base  neutral salt + water 2. Strong acid + weak base  acidic salt + water 3. Weak acid + strong base  basic salt + water Weak acid + weak base  ? Further tests must be performed to determine the type of salt

You must also be able to determine the parent acid and parent base of a salt to determine what type of salt it is FeSO4 The metal Fe comes from the base Fe(OH)2-weak base The nonmetal SO4 comes from the acid  H2SO4-strong acid Therefore…FeSO4 is an acidic salt How about CaCl2… The Ca comes from the base  Ca(OH)2-strong base The nonmetal Cl comes from the acid  HCl-strong acid Therefore…CaCl2 is a neutral salt

What is a salt? A salt is the product (other than water) of a neutralization reaction; an ionic substance consisting of a metallic cation (not H+) and nonmetal anion (not OH-) NaCl FeSO4

4. Titration A process of determining the concentration of an unknown solution by a reaction with a solution of known concentration The formula is on Table T but we must adjust it slightly (#H+)(MA)(VA) = (#OH-)(MB)(VB) One liter of 1 M NaOH will completely neutralize one liter of what concentration of H2SO4? (#H+)(MA)(VA) = (#OH)(MB)(VB) (2)(x)(1) = (1)(1)(1) X = .5 M

HCl titrated against NaOH 1 mole of H+ neutralizes 1 mole of OH- HCl titrated against Ca(OH)2 1 mole of H+ neutralizes .5 mole of Ca(OH)2

If you are just asked concentration, use the Molarity formula When reading a question, if you see the words “neutralize”, “titrate” or “endpoint”, that is your signal to use the titration formula. If you are just asked concentration, use the Molarity formula and if necessary, the moles formula

Acidity and Alkalinity of Solutions When [H+] > [OH-] the solution is acidic (acidity) When [H+] = [OH-] the solution is neutral When [H+] < [OH-] the solution is basic (alkalinity) A scale, called the pH scale, has been developed to express [H+] as a number from 0 to 14. A pH of 0 is strongly acidic, a pH of 7 is neutral and a pH of 14 is strongly basic. The pH scale is logarithmic. Each pH change signifies a tenfold change in the concentration of the hydrogen ion.

Because [H+] and [OH-] are directly related, a pH change one unit represents a tenfold increase or decrease of both the hydrogen ions and hydroxide ion concentration. As the concentration of the hydrogen ion increases, the concentration of the hydroxide ion decreases

As pH changes from 4 to 5, [H+] decreases by a factor of 10 and [OH-] increases by a factor of 10 As pH changes from 6 to 3, [H+] increases by a factor of 1000 and [OH-] decreases by a factor of 1000 If the pH of a solution was 8 and the hydroxide concentration increased a hundredth fold, what is the new pH? 10 If the pH of a solution was 4 and the hydroxide concentration is now 1/10 of the original amount, what is the new pH? 3

the [H+] increases 100 fold. What is the new pH of the lake? If nitric acid is spilled into a lake with an original pH of 5, the [H+] increases 100 fold. What is the new pH of the lake? 3 pH + pOH = 14 [H+][OH-] = 1 x 10-14 [H+] [OH-] pH pOH Acidic or Basic 1 x 10-3 1 x10-11 3 11 acidic 1 x 10-9 1 x 10-5 9 5 basic 1 x 10-8 1 x 10-6 8 6

Acid-Base Indicators An indicator is a substance that changes its color when it gains or loses a proton Each indicator has a unique color change that occurs over a specific pH range See Table M

A solution was yellow in bromthymol blue and blue in bromcresol green. According to Table M, what could be the pH of the solution? Between 5.4 and 6.0 A solution was tested with a pH meter and found to have a pH of 7.8. What color would the solution have if the following indicators were added? Bromthymol blue- b. Thymol blue- blue yellow