Acids & Bases Acids and Bases OBJECTIVES 1- Identify the physical and chemical behaviors of acids and bases. 2-Define acids and bases according to the Arrhenius, and Bronsted-Lowry theories. 3- Describe neutrality and relative acidity and alkalinity in terms of pH measured using Universal Indicator paper. 4- Relate hydrogen ion concentrations to the pH scale and to acidic, basic, and neutral solutions. 5- Distinguish between strong and weak acids and bases in terms of the extent of dissociation, reaction with water and electrical conductivity. 6- Describe the characteristic properties of acids as reactions with metals, bases, carbonates and effect on litmus and methyl orange. 7- Describe the characteristic properties of bases as reactions with acids and with ammonium salts and effect on litmus and methyl orange. Gloves must be worn all the time Corrosive Corrosive Gloves must be worn all the time Several types of acids and where they are found: • Hydrochloric acid: Stomach acid – Sour taste • Acetic acid: An ingredient in vinegar • Citric acid: Citrus fruit like: Lemons, oranges and grapefruit. • Lactic acid: Sour milk, sour cream, yogurt, … Several types of bases and how they are used: • Ammonia: (NH3) Used in household cleaning materials and in fertilizers • Calcium hydroxide: ( Ca(OH)2) It helps to neutralize acidic soil • Sodium hydroxide: (NaOH) One of the strongest bases, used in oven and drain cleaners. • From the vinegar in your kitchen cabinet to the soap in your shower, acids and bases are everywhere! • But what does it mean to say that something is acidic or basic? In order to answer this question, we need to examine some of the theories describing acids and bases. Arrhenius , Bronsted-Lowry, and Lewis Theories Self-Ionization of Water Acids - Arrhenius definition • An acid is any substance that, when added to water, increases the hydronium ion (H3O+) + HCl H + Cl Acids - Arrhenius definition • A strong acid ionizes completely in a solvent HNO3 + H2O H+ + NO3• A weak acid releases few hydrogen ions in aqueous solution HOCl + H2O H3O+ + ClO- https://www.youtube.com/watch?v=DupXDD87oHc Practice Which of the following is a weak acid? A. HCl + H2O H3O+ + Cl- B. CH3COOH + H2O H3O+ + CH3COOC. H2SO4 + H2O H3O+ + HSO4- D. HBr + H2O H3O+ + Br- Bases – Arrhenius definition • A base is any substance that, when added to water, increases the hydroxide ion (OH-) Practice 1. What ion is characteristic of aqueous solutions of all acids? 2. Complete the following equations A. HBr + _______ _______ + BrB. KOH + _______ OH- + _______ C. H2SO3 + H2 O H3O+ + _______ Drawbacks of Arrhenius Definition • Limited to aqueous solutions only • E.g HCl should be considered an acid in aqueous or gaseous form • Cannot classify substances that can act both as an acid and a base Acid – Brønsted-Lowry • A substance that donates a proton (H+) to another substance • All Arrhenius acids are Brønsted-Lowry acids https://www.youtube.com/watch?v=ZiokqP0aZ1E Base - Brønsted-Lowry • A substance that accepts a proton (H+) • All Arrhenius bases are Brønsted-Lowry bases Donates an H+ NH3 + HCl NH4+ + Cl- Accepts an H+ Conjugate Acids and Bases https://www.youtube.com/watch?v=ZiokqP0aZ1E Conjugate Acids and Bases Conjugate Acids and Bases Practice: identify the acid, base and their conjugates H2SO4 + SO32- HSO4- + HSO3- Determine the acid, base, conjugate acid and conjugate base for each of the following Amphoteric Species • Describes a substance that has the properties of an acid and also a base HCO3- + NH3 CO32- + NH4+ HCO3- + H3O+ H2CO3 + H2O Strength of Acids and Bases • A strong acid or base ionizes completely in a solvent HCl H+ + Cl• A weak acid or base releases few ions in aqueous solution CHCOOH + H2O CHCOO- + H3O+ Practice • Compare a strong, dilute acid with a weak, concentrated acid • Identify the conjugate acid base pair: NH3 + H2O OH- + NH4+ H2SO4 + SO32- HSO4- + HSO3• Define amphoteric and give one example • Compare bronsted-lowry definition with Arrhenius definition of an acid and base Common Strong Acids and Bases Common Weak Acids and Bases Reactions of Acids 1. 2. 3. 4. 5. Metals Metal Oxides/Metal Hydroxides Carbonates Litmus Methyl Orange Reaction of Metals with Acids Metal + Acid Salt + Hydrogen For example 2HCl(aq) + Mg(s) MgCl2(aq) + H2(g) Hydrochloric + Magnesium Acid Magnesium + Hydrogen Chloride Metal Reactivity Series To react with an acid the metal needs to be higher than hydrogen in the reactivity series. Reactions of Acids - Metals • E.g. Complete the following reactions: Zn + H2SO4 ________ + ________ Na + HCl _________ + ________ Salts from Acids Remember: Hydrochloric acid (HCl) makes chlorides (Cl-). Sulfuric acid H2SO4 makes sulfates (SO42-) Nitric acid (HNO3) makes nitrates (NO3-) Practice 1. 2. 3. 4. 5. 6. Mg + HCl H2SO4 + Fe HNO3 + K Na + CH3COOH Ca + HF HBr + Fe Reactions of Acids – Metal Oxides/Metal Hydroxides Metal Oxide + Acid Water + Metal Salt Metal Hydroxide + Acid Water + Metal Salt • E.g. Complete the following reactions: NaOH + H2SO4 ________ + ________ KOH + HCl _________ + ________ CaO + HNO3 _______ + ________ Practice 1. Ca(OH)2 + HCl 2. H2SO4 + KOH 3. HNO3 + FeO Reactions of Acids - Carbonates Metal Carbonate + Acid Carbon Dioxide + Metal Salt + Water • E.g. Complete the following reactions: MgCO3 + H2SO4 ________ + ________ ZnCO3 + HCl _________ + ________ Practice 1. Na2CO3 + HCl 2. H2SO4 + (NH4)2CO3 3. HNO3 + CuCO3 Reactions with Acids - Indicators • Litmus – Turns blue Litmus red • Methyl Orange – turns from orange to pinky red Reactions of Bases 1. Ammonium Salts 2. Litmus 3. Methyl Orange Reactions of Bases – Ammonium Salts Ammonium Salt + Base Water + Metal Salt + NH3 • E.g. Complete the following reactions: NH4Cl + NaOH ________ + ________ NH4Br + Ca(OH)2 _________ + ________ Practice 1. Na2CO3 + HCl 2. H2SO4 + (NH4)2CO3 3. HNO3 + CuCO3 Reactions with Bases - Indicators • Litmus – Turns red Litmus blue • Methyl Orange – turns from orange to yellow Practice – Write a word equation and balanced symbol equation for: • The reaction of copper (II) oxide and sulfuric acid. • The reaction of zinc and hydrochloric acid. • The reaction of magnesium and nitric acid. • The reaction of calcium oxide and sulfuric acid. Summary Acid Base Litmus Blue Red Red Blue Methyl Orange Orange Yellow Orange Pink Carbonates Metal Carbonate + Acid CO2 + Salt + H2O Oxides Metal Oxide + Acid H2O + Salt Hydroxides Metal Hydroxide + Acid H2O + Salt Ammonium Salt + Base H2O + Metal Salt + NH3 Ammonium Salts Metals Metal + Acid Salt + H2 Electrical Conductivity and Strength of Acid and Base • Acids and bases are electrolytes • The more a substance dissociates, the more electrically conductive it becomes Electrical Conductivity and Strength of Acid and Base • A strong acid or base completely dissociates • Strong electrolytes • More ions in solution • Therefore more electrical conductivity Electrical Conductivity and Strength of Acid and Base • A weak acid or base partially dissociates • Weak electrolytes • Less ions in solution • Less electrical conductivity