Chapter 6 Ions: Charged Particles in Solution 97 characteristics of either an acid or a base. That is because in pure water the hydronium and hydroxide ions are always in balance. A base has a pH of 7.1 to 14.0. Blood has a pH of 7.4 and is therefore slightly basic. Ammonia, a common household cleaner, has a pH of 11.0. Sodium hydroxide (NaOH) drain cleaner, which is commonly called lye, has a pH of 14.0. It is a very concentrated base. See 6-6. It is important to understand the difference between strength and concentration of acids and bases. The stronger an acid or base is, the more completely it reacts with water to form ions. A pure acid or base is concentrated. The more water you add, the more dilute the acid or base becomes. Hydrochloric acid is a strong acid whether it is concentrated or diluted with water. In summary, the greater the hydrogen or hydronium ion concentration is, the more concentrated the acid and the lower the pH will be. The greater the hydroxide ion concentration is, the more concentrated the base and the higher the pH will be. See 6-7. It is important to remember that very strong acids and very strong bases will cause severe burns. That is why you need to wear splash goggles whenever you A small difference can determine whether harmful bacteria will be able to grow in a food product. The pH scale was developed to express the degree of concentration of hydrogen or hydronium ions present in a solution. The larger the number of hydronium ions in a solution, the more concentrated the acid will be. A food scientist at a beverage bottling plant developed the pH scale. He was responsible for monitoring the acid level of the beverage during production. He found using the number representing the power of the hydronium ions in the mathematical formula would simplify his records. Thus the lower- case p stands for “power of” and the capital H stands for “hydronium ions.” Figure 6-5 shows the relationship between pH scale, hydrogen or hydronium ions, and hydroxide ions. The pH scale is used to show how the acidity or alkalinity of solutions are related. Note that each number in the pH scale represents 10 times greater or fewer hydronium ions. A solution with a pH of 1.0, such as the hydro- chloric acid in the human stomach, is very concentrated. A cup of coffee with a pH of 5.0 is a dilute acid solution. Acids normally have a pH range of 1.0 to 6.9. Water has a pH of 7.0 and is neutral. It does not exhibit Lightning, volcanoes, and decaying plants can lower the pH of rain to 4.5–5.0. What Causes Acid Rain? The main components in acid rain are linked to sulfur and nitrogen oxides. Sources of these acidic compounds are fossil fuels and vehicle exhaust. What Are the Effects of Acid Rain? Acid rain damages materials, corrodes metals, and eats away buildings and statues. It has a possible negative impact on the health of people living in affected areas. It has effects on agricultural and aquatic ecosystems. Some forested areas have lost trees to excessive acid. Entire lakes and streams have become too acidic to support fish life. Research during the 1970s and 1980s has been inconclusive. Balancing the possible dangers caused by acid rain against the economic costs of correcting the problem is difficult. What concerns do you have about acid rain? What role can you play in helping to control it? STEM Matters Acid Rain In 1852, Robert Angus Smith became Britain’s first official Alkali Inspector. In this role, Smith was responsible for monitoring pollution. He reported on the chemistry of the air in Manchester, England, an industrial city. The closer Smith was to the city, the more acidic it was. However, he found that winds could carry acidic particles 100 to 2,000 kilometers from the city. In 1872, Smith coined the term acid rain. He noted that acid rain damaged plants and materials. Smith also observed that people in affected areas had more cases of bronchitis and pneumonia. In 1972, acid rain gained public attention at the United Nations Conference on the Human Environment. What Is Acid Rain? Normal rainfall has a ph of 5.3 to 6.0 depending on the dissolved particles in the rain. Acid rain is precipitation that has elevated levels of hydrogen ions (low pH). Aquatic wildlife, plants, and infrastructure begin to become damaged at pH levels below 5.3. As rain falls to earth, it dissolves pollutants, lowering the pH to harmful levels. Excess dust can raise the pH of rain to a pH of 7.0 or 8.0. Copyright Goodheart-Willcox Co., Inc.