Chemistry Project: Acids and Bases & the pH Scale

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Acids and Bases are two groups of chemical compounds that generally have opposite

characteristics. They have there own unique traits, acids taste sour, turn litmus red while

bases taste bitter and turn litmus blue. The term pH relates to measuring the acidity or

alkalinity of a solution, such as vinegar, or even a damp substance like soul.

The neutral pH is 7, which is essentially water, with lower numbers indicating acidity and

higher numbers indicating alkalinity. Hydronium ions (H3O+) are formed when water

molecules (H2O) bond with hydrogen ions (H+). Hydronium ions are positively charged

because of their extra hydrogen ion. Hydroxide ions (OH-) are produced when water

molecules (H2O) ionize to become hydronium ions (H3O+) and hydroxide ions (OH-).

Substances with a high concentration of hydroxide ions are bases. Bases have a pH rating

of seven or higher. Solutions of ions conduct an electric current, similar in the way that

wire does. Ions can move about in a solution and carry a charge. If they can do carry the

charge they are electrolytes.

The Bronsted-Lowry theory states that an acid is a proton donor and a base a

proton acceptor. Although the acid must still contain hydrogen, the Bronsted-Lowry

theory does not require an aqueous medium. The Bronsted-Lowry definition of acids and

bases also explains why a strong acid displaces a weak acid from its compounds and

likewise for strong and weak bases. In the Lewis theory of acid-base reactions, bases

donate pairs of electrons and acids accept pairs of electrons. A Lewis acid is any

substance, such as the H+ ion, that can accept a pair of nonbonding electrons. Therefore, a

Lewis acid is an electron-pair acceptor. A Lewis base is any substance, such as the OH-

ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an

electron-pair donor.

Svante Arrhenius was a Swedish chemist who helped lay the foundation of

modern day chemistry. When he was a student, he studied the conductive properties of

electrolytic solutions. In his doctoral thesis he made the theory of electrolytic

dissociation. This theory implies that in electrolytic solutions, the dissolved chemical

compounds in the solution are dissociated into ions, even when there is no current

flowing through the solution. Initially, his theory was thought to be wrong, and his thesis

was given the lowest possible passing grade. However, later on Arrhenius' theory of

electrolytic dissociation became generally accepted, and eventually became one of the

principles of modern chemistry.

The pH scale measures the concentration of H+ and OH-. The pH scale was

developed because the concentration of the solution can vary by many factors over time,

and a pH scale was the easiest way to express the variation of the solution. The pH scale

ranges from 0 to 14. The 0 end of the scale is where the concentration is acidic. After 7 the

concentration starts to become more basic as it increases. Most biological fluids are between

pH 6 and pH 8, and there are a few exceptions to this like stomach acid. Each pH unit

represents a tenfold difference of the H+ and OH- concentration. This makes the pH scale so

compact. A solution of pH 2 is not twice as acidic as a solution of pH 4, but a thousand times

more acidic. So when the pH of a solution changes slightly, it actually changes the

concentrations of H+ and OH- in a large way.

Antacids are drugs that diminish abnormal acidity in the digestive tract or in the

other organs. Those that unite directly with free acid in the stomach are known as direct

antacids. "Remote" antacids, such as the acetates, citrates, and tartrates of the alkalies, act

by being changed into carbonates, thus increasing the alkalinity of the blood. Essentially

you are lowering the acidity in your body by adding a base.

The strength of acids and bases depends on their...
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