Chemistry ch 15:  ACIDS and BASES

Operational definitions - properties

1.  Acids

        a.  tastes sour

        b.  changes the color of certain organic dyes called indicators

        c.  neutralizes basic solutions producing salt and water

d.    produces hydrogen gas when reacting with certain active metals

e.     electrolyte

        f.  corrosive

2.  Bases

        a.  tastes bitter

        b.  feels slippery

        c.  changes the color of certain organic dyes called indicators

        d.  neutralizes acidic solutions producing salt and water

f.      reacts with salts of heavy metals to form an insoluble hydroxide

g.    electrolyte

        h.  often referred to as an alkaloid or alkaline solution

        i.  caustic

Electrolyte:  a substance whose water solution conducts an electric current due to the presence of ions (dissociation)

Naming acids and bases

1. binary acids:  contain two elements only

                hydro- (stem) -ic acid   (exception:  HCN)

2.  ternary acids:  contain three elements; hydrogen, usually oxygen, and a third element (usually a nonmetal);  the third element

and oxygen are usually combined as a polyatomic ion;  also called oxyacids

a.     if the polyatomic ion that is combined with the hydrogen ends in -ate, the acid formed will end with –ic 

(stem)-ic acid

b.    if the polyatomic ion that is combined with the hydrogen ends in -ite, the acid formed will end with –ous 

(stem)-ous acid

        c.  exception:  HCN is named like a binary acid, and most organic acids

        d.  follow trends of the other acids formed from groups of the periodic table

3.        bases:  add "hydroxide "  to end of positive ion name  (if more than one form of positive ion, you must identify with         Roman numerals); except ammonia and organic bases

                                                                                                           O

4.        organic acids contain the carboxyl group (–COOH or  –C–OH);  the –OH is called a hydroxyl group is NOT the same as the hydroxide ion;  it is this hydrogen that is the acidic hydrogen

5.        organic bases can be derivatives of ammonia and contain the amine group (–NH2)

Theories

1.  Arrhenius:  explains why conduct in water solutions;  acids produce H+1, bases produce OH–1

2.  Brønsted-Lowry:  new theory due to increased knowledge of catalysts and non aqueous solutions;  acids donate proton               (p+1), bases accept a proton (p+1)

        a.  a proton (p+1) is a hydrogen ion (H+1)

        b. a bare proton is rarely found free in nature, it combines with a water molecule to make a hydronium ion, H3O+1

        c.  Acid/Conjugate Base and Base/Conjugate Acid:

                1.  an acid donates a proton (H+1):  the remainder becomes the conjugate base (acid minus p+1 = conj. base)

                2.  a base accepts a proton  (H+1) :  the result becomes the conjugate acid  (base plus p+1 = conj. acid)

        d.  therefore acid-base reactions are:  acid + base = conjugate acid + conjugate base

3.  Lewis:  about same time as Brønsted-Lowry; broader theory, used a lot in organic chemistry; acids are electron-pair

        acceptors, bases are electron-pair donators;  need to determine the electron dot diagram:

        a.  an empty space means it can accept a pair of electrons, therefore it is a Lewis acid

        b.  an unshared pair of electrons means it can donate a pair of electrons, therefore it is a Lewis base

Strength of acids and bases: based on how much they ionize

1.  ionization: the dissociation of a substance into positive and negative ions in a water solution

2.  strong acids and bases: ionize almost completely in water solution to form positive and negative ions

        a. acids:  HCl, HBr, HI, HNO3, H2SO4, HClO4 and usually HClO3

        b.  bases:  Group IA and IIA metal hydroxides (except beryllium and magnesium)

3.  weak acids and bases: ionize only slightly in water solutions

        a.  acids:  HCN, H2S, H2CO3, HNO2, CH3COOH, HClO, any not mentioned above and organic acids

  1. bases:  any not mentioned above, NH3 and organic bases

4.     the stronger an acid is, the weaker its conjugate base;  the stronger a base it, the weaker its conjugate acid

Polyprotic acids

1.  acids that have more than one ionizable hydrogen ion; diprotic: two H+1, triprotic: three H+1

2.        the hydrogen ions dissociate in steps, one at a time, get weaker acid with each hydrogen ion dissociating

Acid-base behavior

1.  elements with a high electronegativity:  found on the right side of the chart, nonmetals,  pulls electrons towards self Õ  acid

2.  elements with a low electronegativity:  found on the left side of the chart,  metals,  electrons pulled away from it Õ  base

6.     elements with intermediate electronegativities:  can be either an acid or a base, depending on the other substance it is reacting

with,  these are called amphoteric, 

4.  water is an example of an amphoteric substance

        a.  with a H+1 donor, acts as a base

        b.  with a H+1 acceptor, acts as an acid

Acidic and Basic Oxides (also called anhydrides):  anhydride means without water, they absorb water readily

1.        acid anhydride:  an oxygen containing compound, a nonmetallic oxide, that produces an acid when dissolved in water, these compounds are environmentally important because the burning of fossil fuels produces acidic oxides, when these

combine with water vapor in the air or rain it forms "acid rain"

2.  basic anhydride:  an oxygen containing compound, a metallic oxide, that produces an base when dissolved in water 

Salts and neutralization

1.  neutral: not acidic or basic

2.  neutralization reaction:  acid + base  Õ water + salt;   an acid is (H+1)-nonmetal,  a base is metal-(OH-1),  so the reaction is

        (H+1)-nonmetal + metal-(OH-1) Õ HOH + metal-nonmetal

3.  neutralization doesn’t mean neutral,  it means equal numbers of H+1 and OH-1

4.        salt: crystalline compound composed of the anion (negative nonmetal ion) from an acid and the cation (positive metal ion)

from a base

Four Basic Neutralization Reactions

1.   acid + base Õ salt + water

2.   acid anhydride + base Õ salt + water

3.   acid + base anhydride Õ salt + water

4.   acid anhydride + base anhydride Õ salt

Net ionic equations

1.  ions are written as ions (Does it dissociate? Is it a strong acid or strong base?  Is it a soluble salt?)

2.  molecules are written as molecules

3.  only those species that participate in the "reaction" are written, the spectator ions are omitted

Hydrolysis of a Salt: Acidic or basic salts: produce ionizable H+1 or OH-1 after reacting wth water

Hydrolysis is the reaction of a substance with the water that it is dissolved in.  Sometimes a salt will react with water to form an acidic or basic salt.  This is due to the fact that water does ionize to some degree and therefore there are H3O+1  and OH–1 for the salt ions to react with leaving left-overs that change the pH of the solution.  When acids and bases react, what do they produce?

1.  If a strong acid reacts with a strong base, the resulting salt is a neutral salt because the acid and base ionize completely and all

of the ions stay as ions.

3.        If a weak acid reacts with a strong base, the resulting salt is a basic salt because the weak acid only ionizes slightly and the

strong base ionizes completely.  This leaves left-over OH–1 in solution indicating a basic solution.  

4.        If a strong acid reacts with a weak base, the resulting salt is an acidic salt because the strong acid ionizes completely and the

weak base only ionizes slightly.  This leaves left-over H3O+1 in solution indicating a acidic solution.  

5.        If a weak acid reacts with a weak base, the resulting salt could be neutral, acidic or basic depending on how weak the acid and base are in relation to each other.

You can tell if a salt is neutral, acidic or basic by looking at the acid and base that reacted to form the salt.  Remember that a salt is made from the positive metal ion of a base and the negative nonmetal ion of an acid.