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Acids, Bases and Salts Version 1.0 1 Acid Properties • sour taste • change the color of litmus from blue to red. These properties are due to the release • react with of hydrogen ions, H+, in water solution. – 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. 2 Base Properties • bitter or caustic taste • a slippery, soapy feeling. • the ability to change litmus red to blue • the ability to interact with acids 3 Uses of acids and bases Many of the things we eat & use today are made up of acids and bases. Examples: Sulfuric acid-car batteries,acid rain Hydrochloric acid-stomach acid Sodium hydrogen carbonate-baking soda and cooking 4 Uses of Acids/ Bases Contd. , DNA,the building block of life, stores genetic information. Amino acids, the building blocks of proteins. Found in movies: Acids in Jurassic Park (DNA) and in Aliens (acidic blood). 5 Arrhenius Acid/Base Definition • Svante Arrhenius was a Swedish scientist who lived from 1859-1927. • In 1884 he advanced a theory of acids and bases. 6 An Arrhenius acid “is a hydrogencontaining substance that dissociates to produce hydrogen ions.” HA → H+ + AAcid 7 An Arrhenius base is a hydroxidecontaining substance that dissociates to produce hydroxide ions in aqueous solution. MOH → M+(aq) + OH-(aq) Base 8 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. 9 Bronsted and Lowry Definition • J.N. Bronsted (1897-1947) was a Danish chemist and T. M. Lowry (1847-1936) was an English chemist. • In 1923 they advanced their theory of acids and bases. 10 A Bronsted-Lowry acid is a proton (H+) donor. A Bronsted-Lowry base is a proton (H+) acceptor. 11 proton acceptor Bronsted-Lowry Acid Bronsted-Lowry Base proton donor HCl (aq) + H2O(l) → H3O+(aq) + Cl-(aq) 12 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 H3PO4. 3. Write conjugate acid of NO3- 1. No, they differ by 2 protons. 2. H3PO4. 3. HNO3 13 . A strong acid has a weak conjugate base and vice versa. List of strong Acids: HCl, HNO3, H2SO4, 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, HNO3, H C2H3O2 Diprotic Acids: Have two protons that can be donated. H2SO4 Polyprotic Acids: Have more than two protons that can be donated. Ex. H3PO4 14 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?) HCl(g) + H2O (l) → Cl-(aq) + H3O+(aq) Acid 1 Base 2 Base 1 Acid 2 If strong acid will completely ionize 15 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. 16 A Lewis acid is an electron-pair acceptor. A Lewis base is an electron-pair donor. 17 Electron Pair Lewis Acid Acceptor Electron pair donated to H+ Lewis Base Electron Pair Donor 18 19 Reactions of Acids In aqueous solution, the H+ or H3O+ ions are responsible for the characteristic reactions of acids. 20 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: HBr(aq) + KOH(aq) → KBr(aq) + H2O(l) acid base salt 2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l) acid base salt 21 The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water: HBr(aq) + KOH(aq) → KBr(aq) + H2O(l) acid base salt 2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l) acid base salt 22 Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH- and O2- excluded). Salts are usually Chemists use thecrystalline terms ionic and compound have high and saltand melting interchangeably. boiling points. 23 Salt Formation The negative positive ion ion of the salt is derived from the acid. base. base NaOH HCl acid NaCl salt 24 Ionization of Water 25 hydroxide ion Water ionizes slightly. hydronium ion H2O + H2O → → H3O+ + OHacid → base acid base Water ionization equilibrium can be expressed more simply as: Kw= [H3O+] [OH-] = 1.0 x 10-14 mol/L (This expression can be used to calculate H+ or OH-) [H3O+] or [H+]= [OH-] = 1.0 x 10-7 mol/L What is [OH-], if [H+] is 3.0 x 10-3? ( ans: 3.3 X 10 –12 ) 26 Two out of every 1 billion water molecules are ionized . Introduction to pH 27 The pH Scale The pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration. pH= -log [H3O+] The pOH of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration. pOH= -log[OH-] [H3O+] 1.0 Increasing acidity 1.0x10-7 Increasing basicity 1.0x10-14 28 Calculation of pH 29 [H+] = 1.0 X 10 ^-14/ [OH-] H+ OH[OH-] = 1.0 X 10 ^-14/ [H+] pOH= -log [OH-] [OH-]= 10^-pOH [H+]= 10^-pH pH= -log [H+] pH BOX pOH= 14- pH pOH pH pH= 14- pOH 30 pH = -log[H+] [H+] = 1 x 10-5 when this number is exactly 1 pH = this number without pHthe = 5minus sign. 31 pH = -log[H+] [H+] = 2 x 10-5 when this number is one significant figure between 1 and 10 pH is between this number and next ph = 4.7 lower number (4 and one decimal place 5). The number of decimal places of a logarithm is equal to the number of significant figures in the 32 original number. What is the pH of a solution with an [H+] of 1.0 x 10-11? 2 significant figures pH = - log(1.0 x 10-11) pH = 11.00 2 decimal places 33 What is the pH of 0.002 M H2SO4? [H+] = 2 x 10-3 pH = - log(2 x 10-3) pH = 2.7 34 1. What is the pH of 0.003 M NaOH? [OH-] = 3 x 10-3 pOH = - log(3 x 10-3) pOH = 2.2 14.0-2.2 = 11.8 2. What is [H+], if pH is 3.4? 10 -3.4 = 4 X 10 -4 35 The pH scale of Acidity and Basicity 36 15.4 Neutralization 37 Neutralization: The reaction of an acid and a base to form a salt and water. HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) acid base salt 38 Titrations 39 titration: The process of measuring the volume of one reagent required to react with a measured mass or volume of another reagent. 40 42.00 mL of 0.150 M NaOH solution is required to neutralize 50.00 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) + H2O(l) acid base salt Calculate the liters of NaOH that react. mol Molarity = L 1L = 0.04200 42.00 mLThe unit of volume when L Convert mL of NaOH to 1000 mL using molarity is liters. liters of NaOH Calculate the moles of NaOH that react. 0.150 mol NaOH 0.004200 L = 0.00630 mol NaOH 41 1L 42.00 mL of 0.150 M NaOH solution is required to neutralize 50.00 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) + H2O(l) acid base salt The moles mole ratio of NaOH of HClthat to NaOH react equals is 1:1 the moles of HCl that react. 0.00630 mol NaOH react. 0.00630 mol HCl react. The molarity of the HCl solution is mol 0.0630 mol HCl M= = 0.126 M HCl 42 L 0.05000 L Writing Net Ionic Equations 43 In the un-ionized equation all compounds are written using their molecular or formula expressions. HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) acid base salt In the total ionic equation all ions present in solution are written. (H+ + Cl-) + (K+ + OH-) → K+ + Cl- + H2O that do notonly participate in a chemical In the net ionicIons equation the ions that react + Cl ion does K ion not does react. not react. reaction are called spectator ions. are written. H+(aq) + OH-(aq) → H2O(l) 44