Acids and Bases (1) PDF

Table of Contents Acids, Bases, and Salts  Acids An acid is a substance that produces hydrogen ions in a water solution. It is the ability to produce these ions that gives acids their characteristic properties.  Properties of Acids What acids have in common, is that th...

Table of Contents Acids, Bases, and Salts  Acids An acid is a substance that produces hydrogen ions in a water solution. It is the ability to produce these ions that gives acids their characteristic properties.  Properties of Acids What acids have in common, is that they contain at least one hydrogen atom that can be removed when the acid is dissolved in water. When an acid dissolves in water, H+ ions interact with water molecules to form H3O+ ions, which are called hydronium ions. Properties of Acids Acids have several common properties including: All acids taste sour, but taste should never be used to test for the presence of acids. Acids are corrosive Although some acids can burn and are dangerous to handle, most acids in foods are safe to eat.  Properties of Acids Acids also react with indicators to produce predictable changes in color. An indicator is an organic compound that changes color in acid and base. For example, the indicator litmus paper turns red in acid.  Common Acids At least four acids (sulfuric, phosphoric, nitric, and hydrochloric) play vital roles in industrial applications. This lists the names and formulas of a few acids, their uses, and some properties.  Bases Any substance that forms hydroxide ions, OH−, in a water solution is a base. In addition, a base is any substance that accepts H+ from acids. Some foods, such as egg whites, are slightly basic. Medicines, such as milk of magnesia and antacids, are basic, too.  Properties of Bases One characteristic of bases is that they feel slippery, like soapy water. Bases are important in many types of cleaning materials. Strong bases are corrosive, and contact with skin can result in severe burns. Therefore, taste and touch never should be used to test for the presence of a base.  Properties of Bases One way to think about bases is as the complements, or opposites, of acids. In the pure, undissolved state, many bases are crystalline solids. In solution, bases feel slippery and have a bitter taste.  Properties of Bases Strong bases are corrosive, and contact with skin can result in severe burns. Therefore, taste and touch never should be used to test for the presence of a base. Bases react with indicators to produce changes in color. The indicator litmus turns blue in bases.  Common Bases You probably are familiar with many common bases because they are found in cleaning products used in the home. This table includes uses and some information about bases.  Common Uses of Bases Some drain cleaners contain NaOH, which dissolves grease and small pieces of aluminum. The aluminum reacts with NaOH, producing hydrogen and dislodging solids, such as hair.  Ionization of Acids Many of the products that rely on the chemistry of acids and bases are solutions, such as the cleaning products and food products mentioned previously. The acid separates into ions and the hydrogen atom combines with a water molecule to form hydronium ions (H3O+), this is called Ionization. When hydrogen chloride dissolves in water, a hydronium ion and a chloride ion are produced.  Dissociation of Bases When bases that contain –OH dissolve in water, the negative areas of nearby water molecules attract the positive ion in the base. The positive areas of nearby water molecules attract the –OH of the base. The base dissociates into a positive ion and a negative ion⎯a hydroxide ion (OH−).  Dissociation of Bases Unlike acid ionization, water molecules do not combine with the ions formed from the base.  Ionization of Bases Ammonia is a base that does not contain –OH. In a water solution ionization takes place when the ammonia molecule attracts a hydrogen ion from a water molecule, forming an ammonium ion (NH4+). This leaves a hydroxide ion (OH−).  Strong and Weak Acids and Bases The strength of an acid or base depends on how many acid or base particles form into ions in water. When a strong acid dissolves in water, nearly all the acid molecules form into ions. When a weak acid dissolves in water, only a small fraction of the molecules dissolve in water.  Strength and Concentration The terms strong and weak are used to classify acids and bases. The terms refer to the ease with which an acid ionizes or base dissociates in solution. Strong acids and bases ionize or dissociate completely; weak acids and bases ionize or dissociate only partially. Strength and Concentration In contrast, the terms dilute and concentrated are used to indicate the concentration of a solution, which is the amount of acid or base dissolved in the solution. Strength and Concentration It is possible to have dilute solutions of strong acids and bases and concentrated solutions of weak acids and bases.  pH of a Solution The pH of a solution is a measure of the concentration of H+ ions in it. The greater the H+ concentration is, the lower the pH is and the more acidic the solution is. The pH measures how acidic or basic a solution is.  pH of a Solution Solutions with a pH lower than 7 are described as acidic. Solutions with a pH greater than 7 are basic. A solution with a pH of exactly 7 indicates that the concentrations of H+ ions and OH¯ ions are equal. These solutions are considered neutral.  pH of a Solution One way to determine pH is by using a universal indicator paper. This paper undergoes a color change in the presence of H3O+ ions and OH‾ ions in solution. The final color of the pH paper is matched with colors in a chart to find the pH.  Blood pH In order to carry out its many functions properly, the pH of blood must remain between 7.0 and 7.8. main reason for this is The that enzymes, cannot work outside this pH range. Your blood contains compounds called buffers that enable small amounts of acids or bases to be absorbed without harmful effects. Buffers are solutions containing ions that react with additional acids or bases to minimize their  Neutralizatio n Neutralization is a chemical reaction between an acid and a base that takes place in a water solution. For example, when HCI is neutralized by NaHCO3, hydronium ions from the acid combine with hydroxide ions from the base to produce sodium chloride, carbon dioxide, and neutral water.  Neutralizatio n A salt is a compound formed when the negative ions from an acid combine with the positive ions from a base.  Acid-Base Reactions The following general equation represents acid- base reactions in water. Another neutralization reaction occurs between HCI, an acid, and Ca(OH)2, a base producing water and the salt CaCl2.  Salts Salt is essential for many animals large and Most small. salts are composed of a positive metal ion and an ion with a negative charge, such as Cl− or CO32−. Ammonium salts contain the ammonium ion, NH4+, rather than a metal.  Soap s Soaps are salts. They have a nonpolar organic chain of carbon atoms on one end and either a sodium or potassium salt of a carboxylic acid (kar bahk SIHL ihk), –COOH, group at the other end.  Soap s To make an effective soap, the acid must contain 12 to 18 carbon atoms. If it contains fewer than 12 atoms, it will not be able to mix well with and clean oily dirt.  Soap s The long hydrocarbon part of a soap molecule mixes well with oily dirt while the ionic end attracts water molecules. Dirt now linked with the soap rinses away as water flows over it.