Acid-Base Chemistry

MUHAMMAD FAHAD ANSARI 12IEEM 14

• Centuries ago chemists began to classify substances by grouping them into elements, compounds, and mixtures.

• Then the elements were classifies further into metals and nonmetals. Likewise, compounds were divided into organic and inorganic.

• The organic compounds were eventually grouped into smaller classes such as alcohol, hydrocarbons, ketones, ethers, and so on.

• The inorganic compounds were classified on the basis of their properties such as atomic structure and the bonding these were further classified as acids, bases, slats and so on.

Chemical Substances in Environment

Major Groups (Classes) of Chemical Substances

Inorganic Compounds

Acids, Bases and Buffers

Importance

Acids, bases, and buffers are important to the functioning of the human body and are also of tremendous importance to industry and commerce.

Many foods we eat either contain acids or yield acids as they are digested.

Yet the acid base balance of your body blood must be maintained with very narrow limits, or you will die. The concentration of H+ (acidity) of the blood should be approximately 4X10-8 M.

• If it increases to approximately 6X10-8 M• Or decreases to approximately 2.5X10-8 M death results

So that, blood acidity is maintained at the proper level.

• Theories, • Properties and• Their Composition

What are the Acids and Bases ?

Theories about Acids

Santé Arrhenius (1859-1927) Swedish chemist explains why water solutions of certain substances conduct electricity.

Arrhenius proposed the theory of ionization (Electrolytes).

• He suggested that these substances, which are called electrolytes, dissociate in water to produce charged particles (ions), ions conduct electricity. So that Acids are electrolytes. And when Acid react with metals to yield hydrogen gas (H2).

Arrhenius defined acids as substances that ionize in water to yield hydrogen ions (H+)

• The thing common to all acids is their ability to yield hydrogen ions (H+) in water.

• For example:

• HCl in H2O Yields H+ + Cl-

• HF in H2O H+ + F-

• HBr in H2O H+ + Br-

Bronsted-Lowry Concept about Acids:According to this theory, acids are defined simply as proton donors.

The hydrogen ion is a proton: the hydrogen atom minus its electron.

So acid-base reactions are not limited to reactions between water solutions, as defined by Arrhenius. Lowry; defines any substance which gives up a proton (hydrogen ion H+) in any reaction is an acid. This includes all the substances those are acids according to the Arrhenius concept and many others.

Properties of Acids

Physical StateThe acids occur in all three physical states (gases, liquids, and solids)

• Hydrochloric acid as a gas, • Acetic acid as a liquid and • Boric acid as a solid

• Acids have a sour taste. For example, the sour taste of lemons and other citrus fruits is to due to citric acid, one of the organic acids.

• Acids react with active metals to yield hydrogen. Sodium (Na), potassium (K), calcium (Ca), zinc (Zn), and other active metals react with acids such as hydrochloric and sulfuric to yield hydrogen gas.

• Acids react with bases to yield a salt and water. Bases and salts are two other major classes of inorganic compounds. Hydrochloric acid (HCl) reacts with the base sodium hydroxide (NaOH) to yield ordinary table salt, which is sodium chloride (NaCl), and water.

• Acids are electrolytes; they conduct electricity when dissolved in water. However, in the liquid state pure acid compounds such as HCl do not conduct electricity.

• Acids turn blue litmus red. Litmus is an organic dye that is used as an indicator. It becomes red when exposed to acids and blue when exposed to bases, so it is a convenient way to distinguish between acids and bases.

Acids Composition (Elemental)

• In terms of composition, acids consist of the nonmetallic element, hydrogen covalently bonded to other nonmetallic element.

• The system of naming, the acids centers around the number of oxygen atoms present.

• The most common oxygen containing acids of the nonmetal has three oxygen atoms include halogens (Cl, Br, I) nitrogen (N), and carbon (C).

For Example: HClO3 chloric acid, HBrO3 bromic acid, HIO3 iodic acid, HNO3 nitric acid and H2CO3 carbonic acid.

• Acids of sulfur ( S ) and phosphorous ( P ) contain four oxygen atoms H2SO4 sulfuric acid and H3PO4 phosphoric acid.

• Only sulfur and phosphorous contain four oxygen atoms the rest contain three oxygen atoms.

• The number of hydrogen atoms is the same in all the acids of a given nonmetal.

• Acids of phosphorous contain three hydrogen atoms. The acids of sulfur and carbon contain two hydrogen atoms, all the rest contain only one hydrogen atom.

• Theories,• Composition and • Properties

Bases

Arrhenius considered bases to be substances that ionize in water to yield hydroxide ions (OH-)

• The common bases are metallic hydroxides such as NaOH sodium hydroxide, calcium hydroxide Ca(OH-)2. The metallic hydroxide bases are solids that will conduct electricity in molten state-ionically bonded.

• NaOH in water Na+ + OH-

• Ca (OH-)2 in water Ca2+ + 2OH-

• NH3 + H2O NH4OH NH4+ + OH-

(nonmetallic hydroxide)

Lowry, defines bases as protons (H+) acceptors.

Water acts as a base in the presence of an acid. It accepts a proton (H+) from HCl and becomes a hydronium ion (H3O+).

HCl + H2O H3O+ + Cl-Hydronium ion can give up the proton (H+) and the chloride ion (Cl-) can accept a proton, they are also an acid and base, respectively.

NH3 + H2O = ( ) = NH4+ + OH-

Composition of Bases (Elemental)

• The bases are named by simply naming the metal and adding the word hydroxide, such as sodium hydroxide (NaOH), calcium hydroxide Ca (OH-)2, and aluminum hydroxide Al(OH)3, are the more common bases of the non-transition metals.

• Lowry Concept: the solvent enters into the reaction, and the acids and bases occur in solution are called conjugate pairs. The hydronium ion is the conjugate acid of the base water, and the chloride ion is the conjugate base of the acid HCl.

• Many transition metals may lose varying number of electrons as they react to form compounds.

• Metals may have more then one oxidation number.

• For example, copper (Cu) may lose one or two electrons, forming two different ions: Cu1+, Cu2+. [Cu OH and Cu (OH-)2] are possible.

Salts

Much of the earth’s crust consists of salts. Acids react with bases to form salts and water.

HCl + NaOH NaCl + H2O

Composition and Properties of Salts

• In general, most inorganic salts consist of a metallic element ionically bonded to the nonmetallic element or one of the oxygen containing ions (SO4

2-, CO32-, NO3

- and so on) of the nonmetallic element.

• The properties of the salts are essentially the same as those of the ionically bonded compounds.

• The salts are crystalline solids that have high melting and boiling points, and they are electrolytes. They are generally more soluble in water and more stable to heat than the organic compounds.

• In general binary salts are more stable to heat than the ternary salts.

• The N-to-H bonds in the ammonium ions (NH4+) are covalent, as are the bonds between oxygen and other nonmetals.

Acid-Base Reactions

Acid-Base and Oxidation-Reduction Reactions

• An acid-base reaction is characterized by the exchange of protons (H+) between reactants. One substance the acid, gives up protons; another substance, the base, gains the protons.

• In oxidation-reduction reaction is characterized by the exchange of electron between reactants, one substance loses electrons (or share them more freely) and another substance gains the electrons (or increase its share of them)

Acids and Bases in Water

• Na+OH- + H+NO3- Na+NO3- + H2O(aq) (aq) (aq)base acid salt water

• NH3 + HCl NH4+Cl- (gas) (gas) (solid)base acid salt

Solutions in water are called aqueous solution.

• HCl (in water) H+ + Cl-

• Na+OH- (in water) Na+ + OH-

• H2O + HCl H3O+ + Cl-base acid acid base

The hydronium ion (H3O+) is capable of giving up the proton (to the base) and becoming a water molecule again, it is an acid. Thus the hydronium ion is the conjugate acid of the base water.

Substances other than metallic hydroxides that are bases when dissolved in water

• NH3 + H2O <==> NH4+ + OH-base acid acid base

Acids of Halogens and Other Elements

The acids of Chlorine, Iodine, Fluorine, and Bromine• HClO4Perchloric acid• HClO3Chloric acid• HClO2Chlorous acid• HClO Hypochlorous acid• HCl Hydrochloric acid• HI Hydroiodic acid• HF Hydrofluoric acid• HBr Hydrobromic acid

Acids of Nitrogen• HNO3 Nitric acid• HNO2 Nitrous acid

Acids of Carbon• H2CO3 Carbonic acid

Acids of Sulfur• H2SO4 Sulfuric acid• H2SO3 Sulfurous acid

Acids of Phosphorous• H3PO4 Phosphoric acid• H3PO3 Phosphorous acid

Bases

Bases of non-transition elements• Li, Na, K (OH-)• Ba, Ca, Mg (OH-)2 • Al (OH-)3

Bases of transition elements• Cu1+OH- • Cu2+(OH-)2 • Fe2+ (OH-)2 • Fe3+ (OH-)3

Oxides• Oxygen is a special element when combined with hydrogen; it forms the

very important compound water (hydrogen oxide).

• If one hydrogen of water is displaced by a metallic element, the hydroxide (OH-) bases result.

• Oxygen also combines with both the metallic and nonmetallic elements to form other binary (two-element) compounds.

• Many of these compounds are salts (compounds of metal and nonmetal), however, because of oxygen special role they are often classified as oxides.

Metallic Oxides

• Oxygen readily combines with the metallic elements to form compounds, most of which are ionically bonded.

Properties of Metallic OxidesThe metallic oxides have the same general properties as other ionically bonded compounds. They are solids with high melting and boiling points and high heat stability.

• Na2O + H2O 2NaOH

• CaO + H2O Ca (OH-)2

Nonmetallic Oxides

• Oxygen bonds covalently with the other nonmetallic elements to form oxides.

• A given nonmetallic element may form more than one oxide, partly because oxygen may bond to the element by both covalent and co-ordinate covalent bonds.

• System of naming oxides of the nonmetallic elements is as following:

• CO carbon monoxide CO2 carbon dioxide

• SiO2 silicon dioxide SO2 sulfur dioxide

• SO3 sulfur trioxide N2O3 dinitrogen trioxide

• P2O5 diphosphrous Pentoxide

Properties of Nonmetallic Oxides

• The nonmetallic oxides may be considered to be anhydrides of acids. They form acid in water, the soluble nonmetallic oxides are electrolytes.

• CO2 + H2O = H2CO3 in (H2O) = H3O+ + HCO3-

• SO2 + H2O = H2SO3 in (H2O) = H3O+ + HSO3-