Name ‘Em! HI (aq) HCl (aq) H2SO3 HNO3 HIO4

Acid and Bases

Acid and Bases

Acid and Bases

Properties ACIDS BASES electrolytes electrolytes sour taste bitter taste turn litmus red turn litmus blue react with metals to form H2 gas slippery feel vinegar, milk, soda, apples, citrus fruits ammonia, lye, antacid, baking soda ChemASAP

Properties of acids and bases Acids – Sour taste – Turns blue litmus paper red – Reacts with some metals to produce H2 – Dissolves carbonate salts, releasing CO2 Bases – Bitter taste – Turns red litmus paper blue – Slippery to the touch Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Common Acids and Bases Strong Acids (strong electrolytes) Strong Bases (strong electrolytes) NaOH sodium hydroxide KOH potassium hydroxide Ca(OH)2 calcium hydroxide HCl hydrochloric acid HNO3 nitric acid HClO4 perchloric acid H2SO4 sulfuric acid Phosphoric acid, H3PO4, is another acid commonly found in the laboratory. It is on the borderline between a strong and weak acid. Weak Acids (weak electrolytes) CH3COOH acetic acid H2CO3 carbonic Weak Base (weak electrolyte) NH3 ammonia NH3 + H2O  NH4OH Kotz, Purcell, Chemistry & Chemical Reactivity 1991, page 145

Acid Nomenclature Review No Oxygen w/Oxygen An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

Acid Nomenclature Review HBr (aq) H2CO3 H2SO3  hydrobromic acid  carbonic acid  sulfurous acid

Common Acids Sulfuric Acid H2SO4 Nitric Acid HNO3 Phosphoric Acid H3PO4 Hydrochloric Acid HCl Acetic Acid CH3COOH Carbonic Acid H2CO3 Battery acid Used to make fertilizers and explosives Food flavoring Stomach acid Vinegar Carbonated water

Common Bases Name Formula Common Name OH1- hydroxide ion Name Formula Common Name Sodium hydroxide NaOH lye or caustic soda Potassium hydroxide KOH lye or caustic potash Magnesium hydroxide Mg(OH)2 milk of magnesia Calcium hydroxide Ca(OH) 2 slaked lime Ammonia water NH3 H2O household ammonia Bases – Bases are ionic compounds that contain the hydroxide ion and a metal cation and have the general formula M(OH)n . – When a base reacts with an acid, it accepts a proton (H+) and is therefore called a proton acceptor. – Aqueous ammonia solution is also a common base. – Replacing a hydrogen atom of NH3 with an alkyl group results in an amine (RNH2), which is also a base. Amines have pungent odors. . NH4OH NH41+ + OH1- ammonium hydroxide

Acid/Base definitions Definition #1: Arrhenius (traditional) Acids – produce H+ ions (or hydronium ions H3O+) Bases – produce OH- ions (problem: some bases don’t have hydroxide ions!)

Arrhenius acid is a substance that produces H+ (H3O+) in water Arrhenius base is a substance that produces OH- in water

Acid/Base Definitions Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor conjugate acid conjugate base base acid

ACID-BASE THEORIES The Brønsted definition means NH3 is a BASE in water — and water is itself an ACID

The pH scale is a way of expressing the strength of acids and bases The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion. Under 7 = acid 7 = neutral Over 7 = base

Titration standard solution unknown solution Titration Analytical method in which a standard solution is used to determine the concentration of an unknown solution. Quantitative analysis — used to determine the amounts or concentrations of substances present in a sample by using a combination of chemical reactions and stoichiometric calculations Titration – A method in which a measured volume of a solution of known concentration, called the titrant, is added to a measured volume of a solution containing a compound whose concentration is to be determined (the unknown) – Reaction must be fast, complete, and specific (only the compound of interest should react with the titrant) – Equivalence point — point at which exactly enough reactant has been added for the reaction to go to completion Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Buret stopcock Erlenmeyer flask

Titration Vocabulary Titrant The substance added to the analyte in a titration (reagent solution) Analyte The substance being analyzed Equivalence point The point in a titration at which the quantity of titrant is exactly sufficient for stoichiometric reaction with the analyte.

Acid-Base Titration Analyte Titrant If the concentration of the titrant is known, then the concentration of the unknown can be determined. Titrant In acid-base titrations, a buret is used to deliver measured volumes of an acid or base solution of known titration (the titrant) to a flask that contains a solution of a base or an acid, respectively, of unknown concentration (the unknown). If the concentration of the titrant is known, then the concentration of the unknown can be determined. Plotting the pH changes that occur during an acid-base titration against the amount of acid or base added produces a titration curve; the shape of the curve provides important information about what is occurring in solution during the titration. Before addition of any strong base, the initial [H3O+] equals the concentration of the strong acid. Addition of strong base before the equivalence point, the point at which the number of moles of base (or acid) added equals the number of moles of acid (or base) originally present in the solution, decreases the [H3O+] because added base neutralizes some of the H3O+ present. Addition of strong base at the equivalence point neutralizes all the acid initially present and pH = 7.00; the solution contains water and a salt derived from a strong base and a strong acid. Addition of a strong base after the equivalence causes an excess of OH– and produces a rapid increase in pH. A pH titration curve shows a sharp increase in pH in the region near the equivalence point and produces an S-shaped curve; the shape depends only on the concentration of the acid and base, not on their identity. For the titration of a monoprotic strong acid with a monobasic strong base, the volume of base needed to reach the equivalence point can be calculated from the following relationship: moles of base = moles of acid (volume)b (molarity)b = (volume)a (molarity)a VbMb = VaMa Analyte

Buret Reading

Why do chemists use titrations?? Quantitative analysis — used to determine the amounts or concentrations of substances present in a sample by using a combination of chemical reactions and stoichiometric calculations

Acidic, basic, or neutral??

The “perfect pink” for a titration with phenolphthalein

Plotting the pH changes against the amount of acid or base added produces a titration curve Equivalence point point at which exactly enough reactant has been added for the reaction to go to completion

Indicator - changes color to indicate pH change pink Example… phenolphthalein is colorless in acid and pink in basic solution endpoint 7 colorless Volume base added

Titration Equivalence point (endpoint) Point at which equal amounts of H+ and OH- have been added. Determined by… indicator color change Most common acids and bases are not intensely colored – Rely on an indicator Endpoint — point at which a color change is observed, which is close to the equivalence point in an acid-base titration dramatic change in pH Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

moles H+ = moles OH- Titration M: Molarity V: volume At endpoint... Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Titration calculation: Calculate the molarity of an acetic acid solution if 34.57 mL of this solution are needed to neutralize 25.19 mL of 0.1025 M sodium hydroxide.