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 Svante Arrhenius was a Swedish scientist who lived from In 1884 he advanced a theory of acids and bases.

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

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

7 An Arrhenius acid solution contains an excess of H + ions. An Arrhenius base solution contains an excess of OH - ions.

8 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.

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

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

11 hydrogen ion does not exist in water hydrogen ion combines with water a hydronium ion is formed

12 HCl(g) → Cl - (aq) baseacid Conjugate acid-base pairs differ by a proton. When an acid donates a proton it becomes the conjugate base.

13 Conjugate acid-base pairs differ by a proton. When a base accepts a proton it becomes the conjugate acid. H 3 O + (aq)H 2 O (l) → acidbase

14 Conjugate acid-base pairs differ by a proton. baseacid HCl(g)+ → Cl - (aq)+H 3 O + (aq)H 2 O (l) acidbase

15 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.

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

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

18 Lewis Acid Electron Pair Acceptor Lewis Base Electron Pair Donor Electron pair donated to B

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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 Reaction with Metals Acids react with metals that lie above hydrogen in the activity series of elements to produce hydrogen and an ionic compound (salt): 2HCl(aq) + Ca(s) → H 2 (g) + CaCl 2 (aq) acid + metal → hydrogen + ionic compound 2H 2 SO 4 (aq) + Mg(s) → H 2 (g) + MgSO 4 (aq)

22 3Zn(s) + 8HNO 3 (dilute) → 3Zn(NO 3 ) 2 (aq) + 2NO(g) + 4H 2 O(l) Reaction with Metals Oxidizing acids react with metals to produce water instead of hydrogen:

23 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

24 2HCl(aq) + Na 2 O(s) → KBr(aq) + H 2 O(l) Reaction with Metal Oxides In an aqueous solution the products are a salt and water. This type of reaction is closely related to that of an acid with a base: 2H 2 SO 4 (aq) + MgO(s) → MgSO 4 (aq) + H 2 O(l) acidmetal oxidesalt acidsaltmetal oxide

25 Reaction with Carbonates Most acids react with carbonates to produce carbon dioxide, water and an ionic compound: 2HCl(aq) + Na 2 CO 3 (aq) → 2NaCl(aq) + H 2 O(l) + CO 2 (g) acidcarbonatesalt H 2 SO 4 (aq) + MgCO 3 (s) → MgSO 4 (aq) + H 2 O(l) + CO 2 (g) acidcarbonatesalt HCl(aq) + NaHCO 3 (aq) → NaCl(aq) + H 2 O(l) + CO 2 (g) acidcarbonatesalt

26 H 2 CO 3 (aq) → CO 2 (g) + H 2 O(l) Carbonic acid (H 2 CO 3 ) is not the product when an acid reacts with a carbonate because carbonate spontaneously decomposes into carbon dioxide and water.

27 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

28 Amphoteric Hydroxides Hydroxides of certain metals are amphoteric, meaning they are capable of reacting as either an acid or a base: Zn(OH) 2 + 2KOH(aq) → K 2 Zn(OH) 4 (aq) + H 2 O(l) Lewis acidbase Zn(OH) 2 + 2HCl(aq) → ZnCl 2 (aq) + 2H 2 O(l) baseacidsalt

29 Reaction of NaOH and KOH with Certain Metals Some amphoteric metals react directly with the strong bases sodium hydroxide and potassium hydroxide to produce hydrogen: 2NaOH(aq) + Zn(s) + 2H 2 O(l) → Na 2 Zn(OH) 4 (aq) + 3H 2 (g) base + metal + water → salt + hydrogen 2KOH(aq) + 2Al(s) + 6H 2 O(l) → 2KAl(OH) 4 (aq) + 3H 2 (g) Lewis acid

30 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.

31 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

32 Ionization of Water

33 Water ionizes slightly. acidbaseacidbase H 2 O + H 2 O → H 3 O + + OH - → → hydronium ion hydroxide ion H 2 O → H + + OH - → → Water ionization can be expressed more simply as: [H 3 O + ] or [H + ] = 1.0 x mol/L [OH - ] = 1.0 x mol/L Two out of every 1 billion water molecules are ionized.

34 Water ionizes slightly. hydronium ion H 2 O → H + + OH - → → Water ionization can be expressed more simply: [H 3 O + ] or [H + ] = 1.0 x mol/L [OH - ] = 1.0 x mol/L hydroxide ion

35 Introduction to pH

36 pH is the negative logarithm of the hydrogen ion concentration. pH = -log[H + ]

37 Calculation of pH

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

39 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

40 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 the next lower number (between 4 and 5). one significant figure ph = 4.7 one decimal place

41 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

42 What is the pH of a solution with an [H + ] of 6.0 x ? pH = - log[H + ] = -(3.22) = decimal places 2 significant figures log[H + ] = log 6.0 x = -3.22

43 What is the pH of a solution with an [H + ] of 5.47 x ? pH = - log[H + ] = -(7.262) = decimal places 3 significant figures log[H + ] = log 5.47 x =

44 The pH scale of Acidity and Basicity 15.4

45Neutralization

46 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

47 Titrations

48 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

51 Writing Net Ionic Equations

52 (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.