Acids, Bases & Salts

An acid is a substance that when dissolved in water releases hydrogen ions (H+). The H+ then combines with + water to form hydronium ions (H3O ). This is described in the equation below.

+ + H + H2O  H3O You have probably heard of many types of acids. Hydrochloric acid is found in your stomach and aids in the digestion of food. Vinegar, tomato juice and citrus fruits are also acids. Carbonic acid is found in most sodas.

Carbon dioxide reacts with water to form carbonic acid which breaks down to CO2 and H2O to give soda its fizz.

The symbol for hydrogen is written first in the formula for an acid. It should be noted that not all substances that contain hydrogen (H) are acids. Methane (CH4) and sugar (C12H22O11) are two examples of substances that contain hydrogen but are not acids. Typically, the first word in the name of acid ends in –ic.

Name of Common Acids Formula Binary or Ternary? Hydrofluoric acid HF Binary Hydrochloric acid HCl Binary

Hydrosulfuric acid H2S Binary

Carbonic acid H2CO3 Ternary

Acetic acid (vinegar) HC2H3O2 Ternary

Sulfuric acid H2SO4 Ternary

Acids can be identified by a number of properties which are listed below: 1. tastes sour 2. conduct electricity 3. react with many metals to produce hydrogen gas 4. neutralize bases

A safe method for identifying an acid is with the use of an indicator. An indicator is a substance that changes color in the presence of an acid or base. One common indicator used for acids is blue litmus. A number of common substances are indicators. Tea and purple cabbage change color in acidic solutions. For instance, lemon juice will cause the color of brown tea to become a golden yellow color. In the chemistry lab, methyl orange and bromothymol blue are two indicators for acids.

Acids often react with metals to produce hydrogen gas (H2). The equation below describes the reaction of hydrochloric acid with zinc metal.

Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g) Acids that produce a large number of hydrogen ions (H+) in water are called strong acids. Hydrochloric acid, nitric acid, and sulfuric acid are strong acids. Acetic acid (vinegar) and acetyl salicylic acid (aspirin) are weak acids. Do not confuse the terms strong and weak with the terms dilute and strong. It is possible to have a dilute solution of a strong acid. The hydrochloric acid in our stomachs is one such example.

Bases: A base is a substance that when dissolved in water releases hydroxide ions (OH-). The equation below describes how sodium hydroxide (NaOH) does this. NaOH  Na+ + OH-

You have probably heard of many kinds of bases. Many are found at home. Household ammonia (NH4OH), milk of magnesia (Mg(OH)2) and lye (NaOH), the active ingredient in Drano. The hydroxide radical (OH-) is always written last in the formula of a base. It should be noted that all substances whose formula contain OH are not bases. Methyl alcohol has the formula CH3OH and it is not a base. The table below gives the names and formulas of some common bases.

Names & Formulas of Common Bases Sodium Hydroxide NaOH

Ammonium Hydroxide NH4OH

Bismuth Hydroxide (peptobismal) Bi(OH)3 Potassium Hydroxide KOH

Bases can be identified by a number of properties which are listed below: 1. tastes bitter 2. conducts electricity 3. feels slippery 4. neutralize acids

As with acids, a safe method for identifying a base is to use an indicator. Red litmus and red cabbage are two common indicators for bases. The snowball bush or hydrangea can be made to have pink or blue flowers depending on whether the soil it is growing in is acidic or basic. In the chemistry lab, phenolphthalein is an indicator that is often to determine whether a solution is a base. It turns a pinkish/purple in basic solutions.

It was mentioned that bases neutralize acids. This means that when proper amounts of an acid are mixed with a base, the hydrogen ion (H+) of the acid reacts with the hydroxide ion (OH-) of the base to form neutral water and salt. The equation below describes this reaction:

NaOH + HCl  NaCl + H2O + - + - + - Na OH + H Cl  Na Cl + H2O Notice that the reaction produces ordinary table salt, sodium chloride, like you might sprinkle on French fries.

Bases that produce large numbers of hydroxide ions in water are strong bases. Sodium hydroxide is an example of a strong base. Again it is possible to have a dilute solution of a strong base.

The pH of a solution tells you how acidic or basic a solution is. For our purposes, the pH scale ranges from 0 to 14. A pH of 0 means that a solution is strongly acidic. A pH of 14 means that the solution is strongly basic. Pure water is neutral and has a pH of 7.

In the lab, the pH of a solution can be found by using Hydrion paper (pH paper). When the paper is moistened with a solution, the paper changes color. The color of the test paper is compared to a color chart. When the colors match, the pH number can be read from the color chart. The chart below gives the pH of some common solutions. Approximate pH values of some common solutions Ocean water 8.5 Egg white 8.0 Milk 6.5 Blood 7.4 Rain water 5.6 Human saliva 6.6

Investigate: What color does red litmus paper turn when it interacts with an acid? A base? What color does blue litmus paper turn when it interacts with an acid? A base? Design a simple experiment to find out. Available materials are: several acidic solutions, several basic solutions, red litmus paper, blue litmus paper, and Hydrion paper (pH paper). Create a procedure and data table. Get both approved by your instructor before proceeding. When you are finished, fill in the red and blue litmus paper rows on the Venn diagram.