Seminar:Chemistry of

Acids and Bases

Freddie Arocho-PerezKaplan UniversitySC155: Introduction to Chemistry

Acids

An acid is a substance that produces hydrogen ions, H+, when dissolved in water.

Example: HCl (Hydrochloric acid) in water.

Acids

The strength of an acid is based on the concentration of H+ ions in the solution.

The more H+ ions, the stronger is the acid.

Acids

Examples:– Sulfuric acid, H2SO4, is manufactured in greater

quantity than any other industrial chemical. It is the acid found in automobile batteries.

– Hydrochloric acid, HCl, is “stomach acid” in the digestive systems of most mammals.

– Phosphoric acid, H3PO4, is used to manufacture phosphate fertilizers. The tart taste of many soft drinks is due to the presence of phosphoric acid.

Bases

A base is a substance that produces hydroxide ions, OH-, when dissolved in water.

Example: NaOH (Sodium hydroxide) in water.

Bases

The strength of a base is determined by the concentration of hydroxide ions (OH-).

The greater the concentration of OH- ions, the stronger is the base.

Mixtures containing bases are often called alkaline.

Bases

Examples:– Sodium hydroxide, NaOH, or lye, is used in the

production of aluminum, glass, and soap. Drain cleaners often contain NaOH because it reacts with the fats and proteins found in grease and hair.

– Calcium hydroxide, Ca(OH)2 , or slaked lime, is made industrially by treating lime (CaO) with water. It is used in mortars and cements.

– Magnesium hydroxide, Mg(OH)2, or milk of magnesia, is an additive in foods, toothpaste, and many over-the-counter medications. Many antacids contain magnesium hydroxide.

Neutralization Reaction

When solutions (mixtures) of an acid and a base are combined, the products are a salt and water.

Acids and bases react to neutralize each other:

HCl + NaOH --> NaCl + H2O

Example:

HBr + KOH --> KBr + H2O

Neutralization Reaction

Observe the reaction between Milk of Magnesia, Mg(OH)2, and HCl.

Milk of magnesia is a mixture of magnesium hydroxide, Mg(OH)2, in water.

The magnesium hydroxide dissolves upon the addition of the acid.

Neutralization Reaction

pH Scale

The strength of an acid or base in a solution is measured on a scale called the “pH scale”.

pH, or “potential of Hydrogen”, is the scale that measures the relative acidity or alkalinity (basic) of a solution.

Solutions are measured from 0 (totally acid) to 14 (totally alkaline or basic), and 7 is neutral.– Acidic solution: pH < 7– Neutral solution: pH = 7– Basic solution: pH > 7

pH Scale

pH Scale

An acid-base indicator is a dye that changes color depending on the pH of the solution.

pH Scale

For more accurate measurements, a pH meter can be used, which measures the voltage in the solution.

pH in Biological Systems

All living things are water-based systems, which mean that they depend heavily on aqueous equilibria, especially acid-base equilibria.

Acid-base and pH concepts are extremely important to Biochemistry, which is the study of the chemistry of biological systems.

pH in Biological Systems

Reasons why we should be concerned about pH in biological systems:– It gives a qualitative measure for many problems in

cell biology and related fields.– The cell environment is always buffered at

approximately pH = 7 (water).– Enzymes are sensitive to pH. The optimal pH for

most enzymes fall in the range of 6 to 8.– Pepsin, a digestive enzyme in the stomach, works

best at pH = 2.

pH and Blood

The optimum blood pH in a healthy body is slightly alkaline and falls within the narrow range of 7.35 and 7.45.

The human body is made of about 75% water, which is necessary for the transportation of nutrients, oxygen, and other biochemical substances.

It is important for this water-based medium to be pH balanced.

pH and Blood

The normal pH of blood running through arteries (large elastic-walled blood vessels that carry blood from the heart to other parts of the body) is 7.45.

The pH of blood in the veins (vessels that transports blood to the heart) is about 7.35.

A variety of factors affect blood pH including what is ingested, vomiting, diarrhea, lung function, endocrine function, kidney function, and urinary tract infection.

pH in Urine, Saliva, Stomach

Normal urine pH averages about 6.0.

Saliva has a pH between 6.0 and 7.4.

Normal stomach pH is between 1.0 and 2.0.

Acids and the Stomach

A peptic ulcer, or lesion in the stomach wall. Ulcers occur when the protective mucosal lining is

penetrated and gastric acid begins to dissolve the stomach.

Acids and the Stomach

Common over-the-counter antacid remedies are bases:– Gaviscon: Al(OH)3

– Maalox: Al(OH)3 and Mg(OH)2

– Mylanta: Al(OH)3 and Mg(OH)2

– Milk of magnesia: Mg(OH)2

Acids and the Stomach

Dissolution testing is a test for measuring the performance of a drug product.

Tablets or capsules taken orally remain one of the most effective means of treatment available.

The effectiveness of such dosage forms relies on the drug dissolving in the fluids of the gastrointestinal tract prior to absorption.

Acid Rain

Sulfur oxide, SO3, is a by-product of the burning of coal or oil.

It reacts with moisture in the air to form sulfuric acid, H2SO4.

It is primarily responsible for acid rain. Statue adorning the Rheims

Cathedral in France has been severely eroded by

acid rain.

Acid Rain

pH Values from freshwater sites across the United States, 2007.

Acid Rain

High acidity in rainfall causes corrosion in building materials.

Marble and limestone (calcium carbonate) react with the acid; structures made from them erode.

This statue at the Field Museum in Chicago shows the effects of corrosion from acid rain and atmospheric pollutants (a).

The same statue after restoration (b).

Practice Exercises

A solution of which pH is acidic?

– 2– 7– 8– 10

Practice Exercises

A solution of which pH is acidic?

–2– 7– 8– 10

Practice Exercises

The pH of a solution is 9.3. This solution is _____.

– Acidic– Basic– Neutral– None of the above

Practice Exercises

The pH of a solution is 9.3. This solution is _____.

– Acidic

–Basic– Neutral– None of the above

Practice Exercises

In a neutralization reaction, the products are _______.

– Salts– A salt and water– A salt and acid– An acid and a base

Practice Exercises

In a neutralization reaction, the products are _______.

– Salts

–A salt and water– A salt and acid– An acid and a base