Acids & Bases Honors Chemistry Mrs. Partridge

Definition of pH pH comes from the French word “pouvior hydrogene” which means hydrogen POWER! So therefore, pH is a measure of the hydrogen concentration in solution

Properties of Acids Acids taste sour Acids effect indicators Blue litmus turns red Methyl orange turns red Acids have a pH lower than 7 Acids are proton (hydrogen ion, H+) donors Acids react with certain active metals, produce H2 (g) and an ionic compound Aqueous solutions are electrolytes – can conduct electricity Acids react with carbonates Acids neutralize bases

Names & Formulas Acids – compounds that produce hydrogen ions when dissolved in water Chemical formula will be HX where X is either a monatomic or polyatomic ion Anion Ending Example Acid Name -ide Cl-, chloride Hydro – (stem)- ic acid Hydro-chloric acid -ate NO3-, nitrate (stem) –ic acid Nitric acid -ite SO32-, sulfite (stem) – ous acid Sulfurous acid

Acids you must know: Strong Acids Weak Acids Sulfuric acid, H2SO4 Phosphoric acid, H3PO4 Hydrochloric acid, HCl Acetic acid, HC2H3O2 Nitric acid, HNO3

Sulfuric Acid Used in the production of paper Highest volume production of any chemical in the U.S. Used in the production of paper Used in production of fertilizers Used in petroleum refining

Nitric Acid Used in the production of fertilizers Used in the production of explosives Nitric acid is a volatile acid – its reactive components evaporate easily Stains proteins (including skin!)

Hydrochloric Acid Used in the pickling of steel Used to purify magnesium from sea water Part of gastric juice, it aids in the digestion of protein Sold commercially as “Muriatic acid”

Phosphoric Acid A flavoring agent in sodas Used in the manufacture of detergents Used in the manufacture of fertilizers Not a common laboratory reagent

Acetic Acid Used in the manufacture of plastics Used in making pharmaceuticals Acetic acid is the acid present in vinegar

Acids are Proton Donors Monoprotic acids Diprotic acids Triprotic acids H3PO4 HCl H2SO4 HC2H3O2 H2CO3 HNO3 Monoprotic – containing 1 ionizable H Diprotic – containing 2 ionizable H Triprotic – containing 3 ionizable H Polyprotic – acids that include both diprotic & triprotic

Ionization of HCl and formation of hydronium ion, H3O+ H2O + HCl  H3O+ + Cl- Proton acceptor Proton donor

Strong Acids vs. Weak Acids Strong acids are assumed to be 100% ionized in solution (good proton donors). HCl H2SO4 HNO3 Weak acids are usually less than 5% ionized in solution (poor proton donors). H3PO4 HC2H3O2 Organic acids

Strong Acid Dissociation

Weak Acid Dissociation

Organic Acids Organic acids all contain the “carboxyl” group, sometimes several of them. The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.

Examples of Organic Acids Citric acid in citrus fruit Malic acid in sour apples Deoxyribonucleic acid, DNA Amino acids, the building blocks of protein Lactic acid in sour milk and sore muscles Butyric acid in rancid butter

Acids Effect Indicators Blue litmus paper turns red in contact with an acid.

Acids Have a pH less than 7

Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl2 + H2(g)

Acids React with Carbonates 2HC2H3O2 + Na2CO3 2 NaC2H3O2 + H2O + CO2

Products of Neutralization HCl + NaOH  NaCl + H2O H2SO4 + Ca(OH)2  CaSO4 + 2 H2O HNO3 + KOH  KNO3 + H2O The products of neutralization are always a ______ and _______. salt water

Acids Neutralize Bases HCl + NaOH  NaCl + H2O Neutralization reactions ALWAYS produce a salt and water.

Effects of Acid Rain on Marble (calcium carbonate) George Washington: BEFORE George Washington: AFTER

Properties of Bases Bases effect indicators Red litmus turns blue Bases taste bitter Bases effect indicators Red litmus turns blue Phenolphthalein turns purple Bases have a pH greater than 7 Bases are proton (hydrogen ion, H+) acceptors Solutions of bases feel slippery Bases neutralize acids

Examples of Bases Sodium hydroxide (lye), NaOH Potassium hydroxide, KOH Magnesium hydroxide, Mg(OH)2 Calcium hydroxide (lime), Ca(OH)2

Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple in a base.

Bases have a pH greater than 7

Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O

Inequalities An acid solution is one in which [H+] is GREATER THAN the [OH-] A basic solution is one in which the [OH-] is greater than [H+] Basic solutions are also known as alkaline solutions

Neutral Solutions The [OH-] is equal to the [H+] pH = 7 Neutralization: An acid and base react in an aqueous solutions to produce a salt and water Double Replacement Reaction HCl + NaOH  NaCl + HOH (H2O) One mole of H+ reacts with one mole of OH-. This stoichiometric ratio means that one mole of acid will neutralize one mole of base

Amphoteric Substances Substances that can act as either an acid or a base Example: water

Acidic and Basic Anhydrides The term anhydrous means without water An acidic anhydride is an acid which has had the water removed Example: HNO3  N2O5 A basic anhydride is a base which has had the water removed Example: LiOH  Li2O

Concentrated vs Dilute Molarity is often used to express the concentration of an acid or base Molarity (M) = moles (mol) / volume in liters (v) Note: strong acids and weaks acids have the capability of being concentrated or dilute!

Indicators A weak acid or base that undergoes dissociation in a known pH range Indicators respond (change colors) to pH changes over a specific range

Net Ionic Equations for Acids and Bases When writing the net ionic equation for a neutralization reaction, strong acids and bases are broken up into their ions, while weak acids and bases are kept as a complete molecule.

Net Ionic Equations for Acids and Bases There are 7 rules to decide whether a substance should be written as an ion or a complete molecule: Binary acids – HCl, HBr, and HI are strong. All other binary acids and HCN are weak. Ternary acids – if the number of oxygen atoms exceeds the number of hydrogen atoms by 2 or more, the acid is strong. Examples: Strong: HClO3, H2SO4 Weak: HClO, H2CO3

Net Ionic Equations for Acids and Bases Polyprotic acids – in the second and subsequent ionizations, acids are ALWAYS weak. Bases – Hydroxides of alkali and alkaline earth metals, except Be, are STRONG bases. All others are weak. Salts – written in ionic form if soluble, and undissociated form if insoluble Oxides – always written in molecular form Gases – always written in molecular form

pH Concept Expressing [H+] in molarity is cumbersome, so Sorensen proposed the pH scale Range: 0 – 14

Calculating pH pH is the negative logarithm of the [H+] pH = -log[H+] pOH is the negative logarithm of the [OH-]. pOH = -log [OH-] Neutral solution has a pOH of 7 and a pH of 7 For all solutions, pOH + pH = 14

Calculating Molarity Molarity can be calculated from a pH or pOH [OH-] = 10-pOH [H+] = 10-pH Use the 10^ or 2nd log button on the calculator

Equivalents An equivalent is the amount of acid (or base) that will give one mole of H+ (or OH-) 1 mole of HCl produces 1 mole of H+ 1 mole of H2SO4 produces 2 moles of H+

Normality (N) Concentration expressed as the number of equivalents of H+ or OH- times the molarity of the solution N = (eq)M Example: 0.2 M H2SO4  0.4 N H2SO4 0.15 M H3PO4  0.45 N H3PO4

Titration Method used to determine the concentration of a solution

Titration A solution of known concentration (the standard) is added to a measured amount of the solution of unknown concentration until an indicator signals the end point The point of neutralization is called the equivalence point – the point in which the number of equivalents of acid and base are equal

Calculations with Titrations Equivalents of Acid = NA x VA Equivalents of Base = NB X VB At equivalence point Equivalents of Acid = Equivalents of Base NA x VA = NB x VB

Buffers Solutions in which the pH remains relatively constant when small amounts of acid or base are added Made up of a weak acid and its conjugate base or a weak base and its conjugate acid

Buffers Buffer capacity is the amount of acid or base that can be added to a buffer solution before a significant change in pH occurs 2 buffer systems are found in blood and are crucial in maintaining the pH of the body