ACIDS AND BASES Dr. Althea R. Arenajo

Conncepts:1. Arrhenius concept (classical) acids- subs which contain H and

when dissolved in water will furnish H1+

base – subs which contain OH group and when dissolved in water, will furnish OH1-

2. Bronsted-Lowry Concept (protonic concept of acidity)

ACIDS and BASES

acids- subs, molecule, ion capable of

giving up a proton to another subs

base – subs, molecule, ion capable of

combining with a proton 3. Lewis concept acid- any specie that can accept a a

pair of electrons base – any specie that can donate a

pair of electron

ACIDS and BASES

Lewis acids are often termed electrophilic because the acidic property maybe looked upon as a ‘seeking’ of electrons from the electron donating base

Hyrogen-ion cocentration or pH H+ = hydrogen ion, a symbol representing the loss of the one and only electron

Strictly speaking, H is a proton Responsible for the acidic nature of subs

ACIDS and BASES

Aprotonic solvents – subs that do not

accept proton, do not behave as acids

Hydroxide ion (OH-) – a radical composed

of a hydrogen atom, an oxygen atom and

an electron giving it a neagtive charge

Responsible for the chemical properites

of alkali Amphoteric subs – subs that may act as

acid or base

ACIDS and BASES

Pure water is always neutral, it contains

same hydronium and dhydroxide ions

Hydronium ion conc – represents the actual acidic intensity of a sol’n Expression of H3O+ conc in aq sol’n is

considered as being limited by the

ionization constant of water to a range

of bet 1x100 and 1X1014 Nornal limit of pH are given as 0 to 14

ACIDS and BASES

Classification of acids: a. Strong acids- are highly ionized ex: HCl, HNO3, H2SO4, b. Weak acids- ionized only slightly ex: HCN, H3BO3, organic acidsThree methods for the det of H3O+conc:

1. Colorometric method - utilizes reagents

called indicators

ACIDS and BASES

Indicators – are weak organic acids or bases in which the undissociated

molecule has one color and the anion

or cation produced by dissociation has

another color Indicators Acid Base

bromophenol blue yellow blue

bromocresol green yellow blue

ACIDS and BASES

methyl orange red yellow methyl red red yellow phenol red yellow red cresol red yellow red phenolphthalein colorless red thymol blue colorless blue2. Potentiometric – based upon measuring the voltage developed when electrode is immersed in solution

ACIDS and BASES

This method is preffered by the USP because of its accuracy, rapidity, and flexibility that can be used in turbid and jelly-like solutions and those contg pigments and proteins

3. Chemical method – is only for scientific interest and not used practically as a method for determining pH

ACIDS and BASES

A variation of the colorimetric method which is more practical includes strips of paper impregnated with an indicator◦Merely dipping the paper in the unknown sol’n produces a color on the paper which can be compared with charts supplied by the manufacture

◦This is of value to diabetic patients for testing the actual acidity of the urine

ACIDS and BASES

Examples of these paper: a. Nitrazine paper (Squibb) b. pHydrion paper (Central Scientific Co.)

c. Alkacid test ribbon ( Fisher Scientific)

d. Accutint paper ( E.H. Sargent & Co)

e. Special pH paper Paul Frank N.Y.) f. Universal pH Indicator paper (Braun-

Knecht-heimann Co) g. Oxyphen paper(J. Einstein Co)

ACIDS and BASES

Buffer – a pair of chemical compound which control a change in pH of sol’n

Factors that cause variation in H+ conc:

a. Alkali in the Glass from cheap bottles

b. Gases as CO2, Cl2 and NH3 in the air

c. Dust particles d. Oxidation e. Introduction of medicinal agents

ACIDS and BASES

Controlling pH is impt in the ff: a. Collyria d. Vit prep b. Oral penicillin e. Alkaloidal sol’n

c. Milk of magnesia f. Parenteral sol’n

A buffer mixture (or buffer pair) is a sol’n composed of weak acid and a salt of the weak acid or a weak base and its salt

A buffer sol’n will resist any great change

in pH

ACIDS and BASES

Buffer system in common use: a. Feldsman’s buffer (pH range 7.0-8.2)

H3BO3 & Na2B4O7 b. Atkins and Pantin Buffer (7.6-11.0)

H3BO3,Na2CO3 & NaCl – useful in the

alkaline range for contact lens sol’n

- introduced the best buffer system

c. Gifford’s buffer (pH range 6.0-7.8)

- slight modification of Atkins/Patin

ACIDS and BASES

Replaced potassium chloride for sodium

chloride and arranged the volumes on a

basis of 30 mL Borate buffers have a buffer range of

from Ph 5 to 11 with greatest capacity at

pH 9 Suitable for ophthalmic, nasal, and exteral application but not for parenteral

ACIDS and BASES

d. Sorensen Phosphate Buffer (pH range

4.5 -8.0) has a greatest capacity at 6.7

- valuable buffer system for the eyes,

pH includes the isohydric point of

tears (pH 7.4) Buffers are used in numeral ways in pharmaceuticals: antacids, ointments

and lotions

ACIDS and BASES

Official Inorganic Compounds1. Boric Acid – Sal Sedativum

Hombergi Free Boric acid is found in sea water,

certain plants, and nearly all fruits Found in th emarket in three forms: a. Transparent, odorless, colorless pearly scales having a smooth

feel b. Six sided triclinic crystals c. White odorless bulky powder

ACIDS and BASES

Test for Identity: a. Turmeric paper turns bownish-red b. Burns with a gree-bordered flamePharmcology: a. Low antseptic property b. Toxic when taken internally c. Toxic when applied to denuded areas

Principal symptoms: depression of the

circulation, vomiting and diarhhea

ACIDS and BASES

followed by shock and coma Associated with scarlatiniform rash giving the appearance of a “boiled lobster”

Preparations:a. Boric acid sol’n –Boracic acid use as eye wash at 3.5% sol’n b. Boric acid ointment - Borofax iontment

c. Boroglycerine Glycerite – suppository

base

ACIDS and BASES

2. Hydroiodic acid - a colorless gas with a penetrating odor

Pharmacologic action: - same with Lugols sol’n, it has systemic

effect becuase the iodine is conveted to

iodide in the GIT Iodides are utilized rather than the free

I2, once absorbed distribute itself uniformly in the extracellular fluid

ACIDS and BASES

Iodide in the body is a source of I2 for the synthesis of triiodothyronine and thyroxin

The daily requirement of I2 is 200 mcg

Lack of sufficient I2 in the diet results in:

a. Enlarge ment of the thyroid gland b. Simple or colloidal goiter I2 in the diet may be insured by the use of iodized salt which contains 0.01% KI

ACIDS and BASES

Lack of sufficient I2 in the diet may result to: enlagrement of the thyroid gland and simple or colloidal goiter

I2 may be supplied using iodized table

salt contg 0.01% KI I2 is an essential component of the

thyroid hormone - goitrous gland has lesser iodine

and amino acid content than normal glands

ACIDS and BASES

Thyrotropine – is the hormone excreted by

the anterior pituitary gland - has bearing on the conversion of I2 to

the iodinated amino acids - controls the release of thyroid hormone

to the circulation, its absence none is

released

ACIDS and BASES

I2 is an essential constituent of the thyroid hormone being present in Mino acids, thyroxin and triiodothyronine

In comparing goitrous gland with normal glands, there is lesser I2 and amino acid content in the former

Therapeutic uses of Iodides:a. Prevention of colloidal goiterb. Ameliorating agent in

hyperthyroidism

ACIDS and BASES

c. Fibrolytic agent in syphylis, leprosy, sporotrichosis, blastomycosis and actinomycosis

d. Expectorant e. Alternative I2 therapy in hyperthyroidism, results to:

a. Drop in metabolic level (6 mg dosage)

b. Involution of the gland As expectorant, have been used in

asthma, chronic and acute bronchitis

ACIDS and BASES

As alternative, in excess of a ceratin level in the body may bring certain irritative phenomena known as “iodism” which is manifested by rashes, headache, conjunctivitis, laryngitis, and the like

Contraindication to I2 therapy:a. Acneb. Tubercolosis, which flare up even in

dormant cases

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3. Hyrochloric Acid Occurs in active volcanoes Pure gastric juice contains from 0.4- 0.5% of free HCl - this conc does not persist in any lenght of time since the acid is neutrlized by the saliva, mucus, and the return flow of the content of the duodenum

ACIDS and BASES

HCl is necessary to the principal digestive function of the gastric juice, its action is upon protein

Sodum chloride is the source of all commercial HCl

HCl is a colorless gas having an acrid irritating odor and acid taste

It is very soluble in water and conducts electricity

ACIDS and BASES

Pharmacologic action of Chloride ion: - together with Na ions is necessary for the osmotic function which they perform

The exracellualr fluid contains about 0.175 of dissociated Na ions

Acidosis- caused by an excess of the chloride ion in the body

Achlorhydria – lack of HCl in the gastric juice

ACIDS abd BASES

4. Phosphoric acid A clear, colorless , and odorless sol’n

Phosphorite (calcium phosphate) – “phosphate rock”, is the largest source

of phosphates for fertilizer Phosphates are found in soil and are essential in the dev’t of fruits and seeds

Metaphosphoric acid constitutes the ‘glacial phosphoric acid’ of commerce

ACIDS and BASES

Pharmacolgic Action of phosphate ion:1. Acts as buffer systems for

maintaining acid-base balance2. Integral part in the metabolism of

carbohydrates3. In combination with calcium to form

calcium phosphate for bone formation

4. Regulates calcium metabolism and calcium level in the blood

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5. Plays a role in the regulation of body

pH because it guards the alkali reserve

When blood calcium is high, the phosphate is low There is a deficiency of calcium in connection with leg cramps occuring in

pregnant women Phosphates are best absorbed from an acid condition in the bowel

ACIDS and BASES

Alkaline condition an dconditions with excess calcium in the intestine will retard the absorption of phosphate

The admin of substantial amounts of sodium biphosphate will result to acid urine

Uses of phosphoric acid: a. Aids in the formation of peptones b. Treatment of lead posoning

ACIDS and BASES

- since it lowers the pH of the blood; it promotes decalfication of the bones and the associated excretion of lead from the bones at the same time

5. Nitric acid Also known as “eau forte” (strong water)

It exists to a slight extent in some waters, the air after a thunderstorm, and in the humus of the soil

ACIDS and BASES

Ammonia results from decomposiiton of vegetable and animal matter

Bacteria oxidizes ammonia to nitric acid and reacts with the constituents of the soil to form nitrates

An azeotropic mixture with water is formed, only up to 68% acid is produced

It is exceedingly hygroscopic and corrosive

ACIDS and BASES

Acts on subs high in protein and stain them yellow, producing a nitro cmpd known as xanthoprotein

Pharmacology of the nitrate ion:1. It has no specific action in the body2. Potassium nitrate is a neutral salt

but is the most potent diuretic of all the salts

it acts by upsetting th eionic balance of the blood and tissue fluids

ACIDS and BASES

6. Sulfuric Acid Is a non-volatile acid commonly known as “oil of vitriol”

Colorless, odorless liquid of oily conssitency and when strongly heated gives off dense, white fumes of SO3

A viscous liquid called “oleum” also known as Nordhausen acid, a fuming sulfuric acid obtained by dissolving SO3 with H2SO4

ACIDS and BASES

Pharmacology of the Sufate ion: 1. Sulfates are not absorbed from the GIT, oral administration does not have a systemic effect

2. The administration in hypertonic sol’n draws water into the lumen and provokes the intestinal contents to peristalsis with consequent movement of the vowel, being a saline cathartic

ACIDS and BASES

3. Injection of sulfates, sod sulfate, brings about diuresis due to the impermeability of the renal tubule cells to the sulfate ion.

This keeps the sulfate in the tubule and preserve it osmotic action which diminishes the re-absorption of water thus promotes diuresis

ACIDS and BASES