ACIDS and BASES

Acid – Base theoriesNaming acids and basesOxidesReactions and properties of acids and basesStrengths of acids and bases

Acid and Base Theories1) Arrhenius Theory

• An acid is a substance that gives H+ ion, when dissolved in water.

For example, hydrochloric acid reacts with water to form hydrogen ions which are transferred to a water molecule to form a hydronium ion (H3O+).

But simply the reaction is: HCl H+ + Cl-

Acids which have one ionizable hydrogen atom per molecule are called monoprotic acids.

Example: HNO3 H+ + NO3

-

Acids which have two ionizable hydrogen atom per molecule are called diprotic acids.

Example: H2SO4 H+ + HSO4

−

HSO4− H⇌ + + SO4

2−

Acids which have three ionizable hydrogen atom per molecule are called triprotic acids.

Example:H3PO4   H⇌ + + H2PO4

–

H2PO4– H⇌ + + HPO4

2–       HPO4

2– H⇌ + +  PO43–       

• A base is a substance that gives OH- ion, when dissolved in water.

NaOH → Na+ + OH−

Ca(OH)2 → Ca2+ + 2OH-

Reaction of NH3 produce OH-:

NH3 + H2O → NH4+ + OH-

so it is a base.

Limitations of the Arrhenius theory

ONLY FOR AQUEOUS SOLUTIONS!!!!!

Acid and Base Theories2) Bronsted-Lowry Theory

• An acid is a proton (hydrogen ion, H+) donor.

• A base is a proton (hydrogen ion, H+) acceptor.

HCO3- and H2CO3

HOH and OH-

are conjugate acid-base pairs.

Conjugate acid-base pairs

• have only got 1 H+ difference in their structures.

To determine whether a substance is an acid or a base,

• count the hydrogens on each substance before and after the reaction.

• If the number of hydrogens has decreased that substance is the acid (donates hydrogen ions).

• If the number of hydrogens has increased that substance is the base (accepts hydrogen ions)

• A- becomes conjugate base of HA and in the reverse reaction it accepts a H from HZ to recreate HA.

• HZ+ becomes a conjugate acid of Z and in the reverse reaction it donates a H to A- recreating Z

• Which pairs are conjugate acid-base pairs?

Example

1) What are the formulae for the conjugate acid of the following species?

• HS-

• CO32-

• NH3

Example

2) What are the formulae for the conjugate base of the following species?

• HS-

• CO32-

• NH3

• H2SO4

Acid and Base Theories2) Bronsted-Lowry Theory

The Bronsted-Lowry theory doesn't go against the Arrhenius theory in any way - it just adds to it.

Naming Acids and BasesA. Naming Acids:

The name of the acid is determined based on the name of the anion, specifically, based on the ending of the anion name.  The three possibilities are listed here:

Anion Name

Acid Name

-ide Hydro-ic acid

-ite -ous acid

-ate -ic acid

Fluoride F-

Chloride Cl-

Bromide Br-

Iodide I-

Sulfide S2-

Cyanide CN-

Sulfite SO32-

Nitrite NO2-

Phosphate PO43-

Nitrate NO3-

Sulfate SO42-

Perchlorate ClO4-

Chlorate ClO3-

Carbonate CO32-

Common Anions

B. Naming Bases

Simply use the normal rules for naming compounds; ionic or covalent depending on the elements in the compound.

Example:

NaOH: Sodium hydroxide

Ca(OH)2: Calcium hydroxide

NH3: Ammonia

Example:

a) Name the following acids and bases:

NaOH:

H2SO3:

H2S :

H3PO4:

NH3:HCN:

Ca(OH)2:

H3P:

Sodium hydroxide

Sulfurous acid

Hydrosulfuric acid

Phosphoric acid

Ammonia

Hydrocyanic acid

Calcium hydroxide

Hydrophosphoric acid

b) Write the formulas of the following acids and bases:

Hydrofluoric acid:

Carbonic acid: Lithium hydroxide: Nitrous acid:

Sulfuric acid: Beryllium hydroxide: Hydrobromic acid:

HF

H2CO3

LiOH

HNO2

H2SO4

Be(OH)2

HBr

Some common acids

Sulfuric acid:

Nitric acid (kezzap):

Hydrochloric acid(tuz ruhu)

Acetic acid/ethanoic acid/ vinegaric acid

Formic acid/methanoic acid» (in ants’ saliva)

H2SO4

HNO3

HCl

CH3COOH

HCOOH

Some common bases/alkalis

Sodium hydroxide(caustic soda):

Potassium hydroxide:

Magnesium hydroxide (milk of magnesia)

Calcium hydroxide

Ammonia

NaOH

KOH

Mg(OH)2

NH3

Ca(OH)2

Oxides

Nonmetal Oxides

Metal Oxides

CO2, SO2, SO3 etc. show acidic properties(acid anhydride)

CO, NO, N2O are neutral(have 1 oxygen atom in the formula)

Na2O, BaO etc. show basic properties(basic anhydrides)

Amphoteric metals show both basic and acidic properties such as Al and Zn

Acidic Property of Nonmetal Oxides• The oxides of nonmetals are usually acidic except NO,

N2O and CO (They are neutral)• When acidic oxides of nonmetals dissolve in water, they

form acidic solutions.

CO2 + H2O H2CO3

SO3 + H2O H2SO4

N2O5 + H2O 2HNO3

P4O10 + H2O 4H3PO4

• Acidic nonmetal oxides react with bases to form salts.

SO3 + 2KOH K2SO4 + H2O

ACIDIC OXIDES When sulfur dioxide (SO2) is dissolved in

water, sulfurous acid is formed.

SO2 + H2O H2SO3

When sulfur trioxide (SO3) is dissolved in water, some sulfuric acid is formed.

SO3 + H2O H2SO4

ACIDIC OXIDES

• Carbon dioxide dissolved in water is in equilibrium with carbonic acid:CO2 + H2O H⇌ 2CO3 (the equilibrium rxn happens

in our blood)

NEUTRAL OXIDES

• They don’t react with water, acids, and bases.

Basic Properties of Metal Oxides• Oxides of metals are usually basic.

Na2O + H2O 2NaOH

BaO + H2O Ba(OH)2

• Basic oxides react with acids to form salts.

CaO + H2SO4 CaSO4 + H2O

BASIC OXIDES

If sodium oxide (Na2O) is added to water,

sodium hydroxide, a base, is formed.

Na2O + H2O 2 NaOH

Amphoteric Oxides

Oxides amphoteric metals are also amphoteric.

Al2O3 + HCl AlCl3 + H2O

Al2O3 + 2NaOH + 3H2O 2NaAl(OH)4

(sodium tetrahydroxoaluminate)

Properties and Reactions of

Acids and Bases

A.Properties of Acids:• Are corrosive• They taste sour• They form solutions w/ pH less than 7 at 25°C.• They turn litmus dye from blue to red• They conduct electricity (electrolyte)

• They react with active metals to form salt and H2 gas.

Mg + 2HCl MgCl2 + H2

• The acids which do not contain oxygen in their structures can not react with semi noble metals Cu, Hg, Ag.The oxy acids (ACIDS HAVING OXYGEN IN THEIR STRUCTURES)react with these metals producing gases other than H2.

Cu + 2H2SO4 CuSO4 + SO2 + 2H2O

3Ag + 4HNO3 3AgNO3 + NO + 2H2O

• They react with metal carbonates and hydrogen carbonates(bicarbonate ion) to give a salt, water and carbon dioxide, which appears as effervescence (bubbles).

Na2CO3 + 2HCl NaCl + H2O + CO2

CH3COOH (aq)+NaHCO3 (aq)NaCH3COO(aq) +H2O (l) + CO2

ethanoic acid metal hydrogen salt water carbon carbonate dioxide

• They react with bases to form salts and water.

HCl + NaOH NaCl + H2O (neutralization)

H+ (aq) + OH- (aq) H2O(l) (net ionic equation)

B. Properties of Bases• They have bitter taste• Aqueous solutions of bases, known as alkali, have

a slippery feel.• They turn the litmus dye from red to blue• They react with fats in the skin to form soaps• They conduct electricity (electrolyte)• The most common bases are the oxides,

hydroxides and carbonates of metals, but a number of other compounds, such as ammonia also acts as a base.

• They only react with amphoteric metals: Zn, Al

Zn + 2NaOH Na2ZnO2 + H2

2Al + 6 NaOH 2Na3AlO3 + 3H2

• If they are soluble in water they give a solution with pH>7 (at 25 oC).

• They react with acids to form a salt. • CaO (s) + 2 HCl (aq) CaCl2 (aq) + H2O (l) base acid salt water

• Amphoteric metals can react with both acids and bases, such as Al, Zn, Sn, Pb, Cr

Al + 6HCl AlCl3 + 3H2

2Al + 6NaOH 2Na3AlO3 + 3H2

• Oxides and hydroxides of amphoteric metals are also amphoteric.

Al2O3 + HCl AlCl3 + H2O

Al2O3 + 2NaOH + 3H2O 2NaAl(OH)4

ZnO + 2 HCl ZnCl2 + H2O

ZnO + 2NaOH + H2O Na2Zn(OH)4

Neutralization

Examples of Acids & Bases

Acids

HCl

H2SO4

HNO3

Juices, Soda

NaOHCa(OH)2

KOHSoap, Ammonia, Baking Soda

Bases

Relative Strengths of acids and Bases

The strength of an acid depends on how easily the proton, H+ is lost or removed from an acid

Two factors determine the acidic strength:

1. The polarity of the bond with H atom: The more polarized the bond is, the more easily the proton is removed and greater the acidic strength.

2. The size of the atom X (in HX): The greater the atom X, the weaker is the bond and greater the acidic strength.

• Periodic Trends for Binary Acids:Down a group: Sizes of the atoms increase.HFHCl Acidic strength increasesHBrHI

Across a period: Polarity of the bond increases.

CH4 NH3 H2O HF

Acidic strength inreases.

• Oxyacids:

HOF

HOCl Acidic strength decreases. H-O HOBr bond ionizes HOI more easily when

the oxygen atom is

bonded to a

more electronegative atom.

• For a series of oxyacids:

HClO HClO2 HClO3 HClO4

Acidity increases

As the number of oxygen atoms increases,The oxidation number of central atom (Cl) increases. This increases the ionization ofO-H bond. Therefore, acidic strength increases.

• Polyprotic Acids and Their Anions:

H3PO4 H2PO4- HPO4

2-

H2CO3 HCO3- Acidity decreases

H2SO4 HSO4-

Organic Acids

Organic acids have carboxyl group (COOH). They are weak acids.

Example:

HCOOH: Formic acid

CH3COOH: Acetic acid

Basic strength

• As the volume of the metal increases, it becomes easier to ionize the OH- ion and the basic strength increases.

• LiOH

• NaOH

• KOH

Basic strength increases