1 Acids, Bases and Salts Version 1.0

2 Acid Properties sour taste change the color of litmus from blue to red. react with –metals such as zinc and magnesium to produce hydrogen gas –hydroxide bases to produce water and an ionic compound (salt) –carbonates to produce carbon dioxide. These properties are due to the release of hydrogen ions, H +, in water solution.

3 Base Properties bitter or caustic taste a slippery, soapy feeling. the ability to change litmus red to blue the ability to interact with acids

4 Uses of acids and bases Many of the things we eat & use today are made up of acids and bases. Examples: n Sulfuric acid-car batteries,acid rain n Hydrochloric acid-stomach acid n Sodium hydrogen carbonate-baking soda and cooking

5 Uses of Acids/ Bases Contd. n, DNA,the building block of life, stores genetic information. n Amino acids, the building blocks of proteins. n Found in movies: Acids in Jurassic Park (DNA) and in Aliens (acidic blood).

6 Arrhenius Acid/Base Definition Svante Arrhenius was a Swedish scientist who lived from In 1884 he advanced a theory of acids and bases.

7 An Arrhenius acid “is a hydrogen- containing substance that dissociates to produce hydrogen ions.” HA → H + + A - Acid

8 An Arrhenius base is a hydroxide- containing substance that dissociates to produce hydroxide ions in aqueous solution. MOH → M + (aq) + OH - (aq) Base

9 An Arrhenius acid solution contains an excess of H + ions because an Arrhenius acid increases H+ concentration, when dissolved in water. An Arrhenius base solution contains an excess of OH - ions because it increases OH- concentration, when dissolved in water.

10 Bronsted and Lowry Definition J.N. Bronsted ( ) was a Danish chemist and T. M. Lowry ( ) was an English chemist. In 1923 they advanced their theory of acids and bases.

11 A Bronsted-Lowry acid is a proton (H + ) donor. A Bronsted-Lowry base is a proton (H + ) acceptor.

12 HCl (aq) + H 2 O(l) → H 3 O + (aq) + Cl - (aq) proton acceptor Bronsted-Lowry Base proton donor Bronsted-Lowry Acid

13 Conjugate acid-base pairs differ by a single proton. 1. Are sulphate and sulfuric acid conjugate acid and base of each other? Why or why not? 2. Write conjugate base of H 3 PO Write conjugate acid of NO No, they differ by 2 protons. 2. H 3 PO HNO 3

14. A strong acid has a weak conjugate base and vice versa. List of strong Acids: HCl, HNO 3, H 2 SO 4, HI, HBr, HClO3, HClO4 List of Strong Bases: All group 1 and 2 metal hydroxides Monoprotic Acids: Have one proton that can be donated. Ex. HCl, HNO 3, H C 2 H 3 O 2 Diprotic Acids: Have two protons that can be donated. H 2 SO 4 Polyprotic Acids: Have more than two protons that can be donated. Ex. H 3 PO 4

15 Compare the strengths of two acids in the following reactions. What does the strength of acid have to do with the direction in which this reaction occurs? (Forward reaction is favored, why?) Base 1 Acid 1 HCl(g)+ → Cl - (aq)+H 3 O + (aq)H 2 O (l) Acid 2 Base 2 If strong acid will completely ionize

16 Lewis Acids and Bases In 1923 G. N. Lewis developed a more comprehensive theory of acids and bases. The Lewis theory deals with the way in which a substance with an unshared pair of electrons reacts in an acid-base type of reaction.

17 A Lewis acid is an electron-pair acceptor. A Lewis base is an electron-pair donor.

18 Lewis Acid Electron Pair Acceptor Lewis Base Electron Pair Donor Electron pair donated to H +

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20 In aqueous solution, the H + or H 3 O + ions are responsible for the characteristic reactions of acids. Reactions of Acids

21 HBr(aq) + KOH(aq) → KBr(aq) + H 2 O(l) Reaction with Bases The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water: 2HNO 3 (aq) + Ca(OH) 2 (aq) → Ca(NO 3 ) 2 (aq) + 2H 2 O(l) acidbasesalt acidbasesalt

22 HBr(aq) + KOH(aq) → KBr(aq) + H 2 O(l) The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water: 2HNO 3 (aq) + Ca(OH) 2 (aq) → Ca(NO 3 ) 2 (aq) + 2H 2 O(l) acidbasesalt acidbasesalt

23 Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH - and O 2- excluded). Chemists use the terms ionic compound and salt interchangeably. Salts are usually crystalline and have high melting and boiling points.

24 NaOHHCl NaCl base acid salt The positive ion of the salt is derived from the base. The negative ion of the salt is derived from the acid. Salt Formation

25 Ionization of Water

26 Water ionizes slightly. baseacid base H 2 O + H 2 O → H 3 O + + OH - → → hydronium ion hydroxide ion Water ionization equilibrium can be expressed more simply as: Kw= [H 3 O + ] [OH - ] = 1.0 x mol/L (This expression can be used to calculate H+ or OH-) [H 3 O + ] or [H + ]= [OH-] = 1.0 x mol/L What is [OH-], if [H+] is 3.0 x ? ( ans: 3.3 X 10 –12 ) Two out of every 1 billion water molecules are ionized.

27 Introduction to pH

28 The pH Scale The pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration. pH= -log [H 3 O + ] The pOH of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration. pOH= -log[OH - ] [H 3 O + ] 1.0 Increasing acidity 1.0x10 -7 Increasing basicity 1.0x10 -14

29 Calculation of pH

30 H+ OH- pH pOH [H+] = 1.0 X 10 ^-14/ [OH-] [OH-] = 1.0 X 10 ^-14/ [H+] pOH= -log [OH-] [OH-]= 10^-pOH pH= -log [H+] [H+]= 10^-pH pH= 14- pOH pOH= 14- pH pH BOX

31 pH = -log[H + ] [H + ] = 1 x when this number is exactly 1 pH = this number without the minus sign. pH = 5

32 pH = -log[H + ] [H + ] = 2 x when this number is between 1 and 10 The number of decimal places of a logarithm is equal to the number of significant figures in the original number. pH is between this number and next lower number (4 and 5). one decimal place one significant figure ph = 4.7

33 What is the pH of a solution with an [H + ] of 1.0 x ? pH = - log(1.0 x ) pH = decimal places 2 significant figures

34 What is the pH of M H 2 SO 4 ? [H + ] = 2 x pH = - log( 2 x ) pH = 2.7

35 1. What is the pH of M NaOH? 2. What is [H+], if pH is 3.4? [OH - ] = 3 x pOH = - log( 3 x ) pOH = = = 4 X 10 -4

36 The pH scale of Acidity and Basicity 15.4

37Neutralization

38 Neutralization: The reaction of an acid and a base to form a salt and water. HCl(aq) + KOH(aq) → KCl(aq) + H 2 O(l) acidbasesalt

39 Titrations

40 titration: The process of measuring the volume of one reagent required to react with a measured mass or volume of another reagent.

mL of M NaOH solution is required to neutralize mL of hydrochloric acid solution. What is the molarity of the acid solution? The equation for the reaction is HCl(aq) + NaOH(aq) → NaCl(aq) + H 2 O(l) acidbasesalt Convert mL of NaOH to liters of NaOH The unit of volume when using molarity is liters. Calculate the moles of NaOH that react. Calculate the liters of NaOH that react.

mL of M NaOH solution is required to neutralize mL of hydrochloric acid solution. What is the molarity of the acid solution? The equation for the reaction is HCl(aq) + NaOH(aq) → NaCl(aq) + H 2 O(l) acidbasesalt The mole ratio of HCl to NaOH is 1:1The moles of NaOH that react equals the moles of HCl that react mol NaOH react mol HCl react. The molarity of the HCl solution is

43 Writing Net Ionic Equations

44 (H + + Cl - ) + (K + + OH - ) → K + + Cl - + H 2 O In the total ionic equation all ions present in solution are written. H + (aq) + OH - (aq) → H 2 O(l) In the net ionic equation only the ions that react are written. HCl(aq) + KOH(aq) → KCl(aq) + H 2 O(l) acidbasesalt In the un-ionized equation all compounds are written using their molecular or formula expressions. K + ion does not react.Cl - ion does not react. Ions that do not participate in a chemical reaction are called spectator ions.