Acids and bases are common substances found in many every day items, from fruit juices and soft drinks to soap. In this unit we'll exam what the properties are of acids and bases, and learn about the chemical nature of these important compounds. You'll learn what pH is and how to calculate the pH of a solution. 14.1: Sour Patch Kids and International Spy Movies Sour Patch Kids are a soft candy with a coating of invert sugar and sour sugar (a combination of citric acid, tartaric acid and sugar). Its slogan, "Sour. Sweet. Gone.", refers to the sour-to-sweet taste of the candy. 14.2: Acids- Properties and Examples Acids are very common in some of the foods that we eat. Citrus fruits such as oranges and lemons contain citric acid and ascorbic acid, which is better known as vitamin C. Carbonated sodas contain phosphoric acid. Vinegar contains acetic acid. Your own stomach utilizes hydrochloric acid to digest food. Acids are a distinct class of compounds because of the properties of their aqueous solutions. 14.3: Bases- Properties and Examples A base is thought of as a substance which can accept protons or any chemical compound that yields hydroxide ions (OH-) in solution. It is also commonly referred to as any substance that can react with an acid to decrease or neutralize its acidic properties, change the color of indicators (e.g. turn red litmus paper blue), feel slippery to the touch when in solution, taste bitter, react with acids to form salts, and promote certain chemical reactions (e.g. base catalysis). 14.4: Molecular Definitions of Acids and Bases Although the properties of acids and bases had been recognized for a long time, it was Svante Arrhenius in the 1880's who determined that: the properties of acids were due to the presence of hydrogen ions, and the properties of bases were due to the presence of hydroxide ions. 14.5: Reactions of Acids and Bases When an acid and a base are combined, water and a salt are the products. Salts are ionic compounds containing a positive ion other than H+ and a negative ion other than the hydroxide ion, OH-. Double displacement reactions of this type are called neutralization reactions. Salt solutions do not always have a pH of 7, however. Through a process known as hydrolysis, the ions produced when an acid and base combine may react with the water to produce slightly acidic or basic solutions. 14.6: Acid–Base Titration- A Way to Quantify the Amount of Acid or Base in a Solution Acid-base titrations are lab procedures used to determine the concentration of a solution. One of the standard laboratory exercises in General Chemistry is an acid-base titration. During an acid-base titration, an acid with a known concentration (a standard solution) is slowly added to a base with an unknown concentration (or vice versa). A few drops of indicator solution are added to the base. The indicator will signal, by color change, when the base has been neutralized (when [H+] = [OH-]). 14.7: Strong and Weak Acids and Bases Acids are classified as either strong or weak, based on their ionization in water. A strong acid is an acid which is completely ionized in an aqueous solution. A weak acid is an acid that ionizes only slightly in an aqueous solution. Acetic acid (found in vinegar) is a very common weak acid. 14.8: Water- Acid and Base in One Water is an interesting compound in many respects. Here, we will consider its ability to behave as an acid or a base. In some circumstances, a water molecule will accept a proton and thus act as a Brønsted-Lowry base. 14.9: The pH and pOH Scales- Ways to Express Acidity and Basicity pH and pOH are defined as the negative log of hydrogen ion concentration and hydroxide concentration, respectively. Knowledge of ether can be used to calculate either [H+] of [OH-]. pOH is related to pH and can be easily calculated from pH. 14.10: Buffers- Solutions That Resist pH Change A buffer is a solution that resists dramatic changes in pH. Buffers do so by being composed of certain pairs of solutes: either a weak acid plus a salt derived from that weak acid or a weak base plus a salt of that weak base.