Chapter 11 Acids, Bases, and Salts

Chapter 11: Acids, Bases, and Salts Definitions and Properties Acids 1. 2. 3. 4. 5. Water (aqueous) solutions of acids conduct electricity. The degree of conduction depends on the acid’s degree of ionization. A few acids ionize almost completely, while others ionize to only a slight degree. Acids will react w/ metals that are more active than hydrogen ions to liberate hydrogen. Some acids are also strong oxidizing agents and will not release hydrogen Acids have the ability to change the color of indicators. Acids react w/ bases so that the properties of both are lost to form water and a salt. ACID + BASE → SALT + WATER Acids react w/ carbonates to release carbon dioxide. - The Arrhenius Theory states that an acid is a substance that yields hydrogen ions in aqueous solution. - Although they are not really not separate ions but become attached to the oxygen of the polar water molecule to form the 𝐻3 𝑂+ ion (the hydronium ion). Ex: The general reaction for the dissociation of an acid, HX, is commonly written as 𝐻𝑋 ⇆ 𝐻 + + 𝑋 − To show the formation of the hydronium ion, the complete equation is: 𝐻𝑋 + 𝐻2 𝑂 ⇆ 𝐻3 𝑂+ + 𝑋 − Bases 1. 2. 3. 4. 5. - Bases are conductors of electricity in an aqueous solution. Their degrees of conduction depend on their degrees of ionization. Bases cause a color change in indicators. Bases react w/ acids to neutralize each other and form salt and water. Bases react w/ fats to form a class of compounds called soaps. Aqueous solutions of bases feel slippery, and the stronger bases are very caustic to the skin. The Arrhenius Theory defines a base as a substance that yields hydroxide ions (𝑂𝐻 − ) in an aqueous solution. - The Bronsted-Lowry Theory defines acids as proton donors and bases as proton acceptors. Ex: 𝐻𝐶𝑙(𝑔) + 𝑁𝐻3 (𝑔) → 𝑁𝐻 + 4 (𝑠) + 𝐶𝑙 − (𝑠) The HCl is the proton donor or acid, and the ammonia is a Bronsted-Lowry base that accepts the proton. Conjugate Acids and Bases In an acid-base reaction, the original acid gives up its proton to become a conjugate base. After losing its proton, the remaining ion is capable of gaining a proton, thus qualifying as a base. The original base accepts a proton, so it's now classified as a conjugate acid since it can release this newly acquired proton and behave like an acid. Acid Concentration Expressed as pH - pH can be defined as −𝑙𝑜𝑔[𝐻 + ]is the concentration of hydrogen ions expressed in moles per liter. - 100 = 102 so logarithm of 100, base 10 = 2 - 10,000 = 104 so logarithm of 10,000, base 10 = 4 - 0.01 =10−2 so logarithm of 0.01, base 10 = -2 Ex: Find the pH of a 0.1 molar solution of HCl. Step 1: Because HCl ionizes almost completely into 𝐻 + and 𝐶𝑙 − , [𝐻 + ] = 0.1 mole/liter. Step 2: pH = −𝑙𝑜𝑔[𝐻 + ] so pH = −𝑙𝑜𝑔[10−1 ] Step 3: The logarithm of 10−1 is -1 so pH = -(-1) Step 4: The pH = 1. B/c water has a normal 𝐻 + concentration of 10−7 mole/liter b/c of the slight ionization of water molecules, the water pH is 7 when the water is neither acidic or basic. - The pOH is the negative logarithm of the hydroxide ion concentration: pOH = −𝑙𝑜𝑔[𝑂𝐻 − ] Ex: If the concentration of the hydroxide ion is 10−9 M, then the pOH of the solutionis +9. [𝐻 + ][𝑂𝐻 − ] =1.0× 10−14 AT 298 K The following relationship can be devised: pH + pOH = 14.00 - In other words, the sum of the pH and pOH of an aqueous solution at 298 K must always equal 14.00. - TITRATION - The use of volume measurement in problems to determine the concentrations of “unknown” solutions or solids is called titration. - A common example uses acid-base reactions. Ex: If you are given a base of known concentration, 0.10 M NaOH and you want to determine the concentration of an HCl solution. - First, introduce a measured quantity, 25,0 mL of the NaOH into a flask by using a pipette. - Next, introduce 2 drops of a suitable indicator. b/c NaOH and HCl are considered a strong base and acid, an indicator that changes color in the middle pH range would be appropriate. Litmus solution could be used as its blue in basic solution but changes to red in acidic. - Slowly introduce HCl until the color change occurs, this is called the end point. - The point at which enough acid is added to neutralize all the standard solution in the flask is called the equivalence point. SALTS - A salt is an ionic compound containing positive ions other than hydrogen ions and negative ions other than hydroxide ions. - Five methods of preparing a salt are: 1. Neutralization reaction. - 2𝐻𝐶𝑙 (𝑎𝑞) + 𝐶𝑎(𝑂𝐻)2 (𝑎𝑞) → 𝐶𝑎𝐶𝑙2 (𝑎𝑞) + 2𝐻2 𝑂(𝑙) - ACID + BASE → SALT + WATER 2. Single replacement reaction. - An active metal replaces hydrogen in an acid. - 𝑀𝑔(𝑠) + 𝐻2 𝑆𝑂4 (𝑎𝑞) → 𝑀𝑔𝑆𝑂4 (𝑎𝑞) + 𝐻2 (𝑔) 3. Direct combination of elements. - 𝐹𝑒(𝑠) + 𝑆(𝑠) → 𝐹𝑒𝑆(𝑠) 4. Double Replacement 5. - When solutions of 2 soluble salts are mixed, they form an insoluble salt compound 𝐴𝑔𝑁𝑂3 (𝑎𝑞) + 𝑁𝑎𝐶𝑙(𝑎𝑞) → 𝑁𝑎𝑁𝑂3 (𝑎𝑞) + 𝐴𝑔𝐶𝑙(𝑠) Reaction of a metallic oxide w/ a nonmetallic oxide. 𝑀𝑔𝑂(𝑠) + 𝑆𝑖𝑂2 (𝑠) → 𝑀𝑔𝑆𝑖𝑂3 (𝑠)