acid

Slide 1: 

Bases Acids and

Earlier concept of acid & base : 

Earlier concept of acid & base An acid may be defined as any substance which has a sour taste and its aqueous solution turns blue litmus red. A base may be defined as any substance which has a bitter taste & its aqueous solution turns red litmus blue.

Slide 3: 

An acid may be defined as any sub. Which gives H+ ions in aqueous solution. A base may be defined as any sub. Which gives OH- ions in aqueous solution. HCl  H+ + Cl– NaOH  Na+ + OH–

Limitations : 

Limitations The definitions of acid & base are only in terms of aqueous solutions and not in terms of substance. The theory is not able to explain acidic and basic properties of substances in non-aqueous solvents. E.g. NH4NO3 in liquid NH3 acts as an acid, though it does not give H+ ions. The neutralization of acid and base in absence of solvent could not be explained. The basic substance which do not contain hydroxide ion would not be explained by the theory. Many organic substances and NH3 which do not have OH- ions at all are actually known to show basic characters. It can’t explain the acidic character of certain salts such as AlCl3 in aqueous solution.

Slide 5: 

An acid may be defined as any hydrogen containing material (molecule, anion or cation) that is capable of donation a proton H+ to any other substance. A base may be defined as any sub. (molecule, anion or cation) that can accept a proton from any other substance. HCl  H+ + Cl– NH4 + H+ + NH3 OH– + H+  H2O

Slide 7: 

The acid base pairs, the members of which can be formed from each other mutually by the gain or loss of proton are called conjugate acid-base pairs.

Slide 9: 

HCl +H2O  H3O+ + Cl– NH3 +H2O  NH4+ + OH–

A strong acid is one which readily donates its proton to a base, so the conjugate base of such an acid must necessarily be weak. General rule is that strong acids have weak conjugated bases and strong bases have weak conjugated acids. : 

A strong acid is one which readily donates its proton to a base, so the conjugate base of such an acid must necessarily be weak. General rule is that strong acids have weak conjugated bases and strong bases have weak conjugated acids.

Limitations : 

Limitations The concept lays excessive emphasis on the proton-transfer. Although it is true that most common acids are protonic in nature, yet there are many which are not. A large number of acid-base reactions are known in which no proton transfer can take place, E.g. Thus the protonic definition can’t be used to explain the rxns occuring in non-protonic solvents, such as COCl2, SO2, N2O4. SO2+SO2  SO2+ + SO32-

Lewis concept (Electron-donor-acceptor system) : 

Lewis concept (Electron-donor-acceptor system) Explain the terms along with the formation of coordinate bond. Acid may be defined as any species that can accept an electron pair to form a coordinate bond. Base may be defined as any species that can donate an electron pair to the formation of coordinate bond. Thus, acid-electron pair acceptor base- electron pair donor

Bronsted acid, i.e. the proton is also a lewis acid but all lewis acids are not bronsted acids. Similar in the case of bronsted bases and lewis bases. : 

Bronsted acid, i.e. the proton is also a lewis acid but all lewis acids are not bronsted acids. Similar in the case of bronsted bases and lewis bases.

Limitations : 

Limitations Lewis acid & base found to depend on the type of rxn, it is not possible to arrange them in any order of their relative strength. This rxn involves electron, they are expected to be very fast rxn. However there are many lewis acid-base rxns which are slow.

Relative strength of acid & base : 

Relative strength of acid & base With respect to strength , two general classes Strong & Weak

Strong acids and bases are ones which are almost completely dissociated in dilute aqueous media.Weak acids and bases are ones which are only partially dissociated in dilute aqueous media. : 

Strong acids and bases are ones which are almost completely dissociated in dilute aqueous media.Weak acids and bases are ones which are only partially dissociated in dilute aqueous media.

The strength of an acid and base is most frequently determined by the dissociation constant K. : 

The strength of an acid and base is most frequently determined by the dissociation constant K.

Slide 19: 

If H2O is a strong base it will have high affinity for H+ and so H3O+ is a weak acid. If H2O is a weak base it will have low affinity for H+ and so H3O+ is a strong conjugated acid.

Slide 20: 

As the dissociation constant Ka value increases, the acidity of substance means acid strength increases, it becomes strong acid. As the dissociation constant Ka value decreases, the acidity of substance means acid strength decreases, it becomes weak acid. So, if Ka value decreases, it becomes base.

Importance of acid-base in pharmacy : 

Importance of acid-base in pharmacy Acid base neutralization rxn find use in preparative procedures for the preparation of suitable salts, and for conversion of certain salts into more suitable forms, specific acid-base system is used for preparing effervescent mixtures. Acid bases are used in analytical procedures which are involving acid-base titrations. Acid and base find use as therapeutic agents in the control of and adjustment of the pH of the gastrointestinal tract, body fluids and urine. The conjugate pairs of acids or bases are used as buffers, e.g. buffer acid as a proton donor and buffer base as a proton acceptor.

Safety Precautions : 

Safety Precautions Inadequate closures give rise to vapourization and loss of gaseous components and to exposure to moisture, oxygen and carbon dioxide. Oxygen may be able to oxidize acids or bases Carbon dioxide can react with bases such as sodium hydroxide, potassium hydroxide, sodalime and lime water. Some hygroscopic substances like NaOH are able to absorb moisture on exposure to air and become liquids showing deliquescent property Dehydrating agents like concentrated sulphuric acid and quick lime have to be protected from air by tight closures.

Hydrogen ion concentration : 

Hydrogen ion concentration

pH scale : 

pH scale

Calculate the pH of a solution in which the hydrogen ion concentration is 4.2x10-4 mol dm-3.calculate the hydrogen ion concentration in a solution of pH 8.32. : 

Calculate the pH of a solution in which the hydrogen ion concentration is 4.2x10-4 mol dm-3.calculate the hydrogen ion concentration in a solution of pH 8.32.

Mechanism of maintaining pH of blood : 

Mechanism of maintaining pH of blood Human body requires ―› oxygen for normal metabolic demands. If hemoglobin is not present in the blood, the solubility of oxygen in blood is very slight. Hb functions as a reversible oxygen carrier, picking up oxygen in the lungs and releasing it in tissues for use in cellular metabolism. The maintenance of a relative constancy of 7.4 of blood pH is vital for oxygen transport.