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Taste sour Form solution that conduct electricity React with metals Turn blue litmus paper to red React with bases to form salt and water Ex: fruit juice, vinegar, milk Form solutions that conduct electricity Slippery or soapy in the skin Taste bitter Turn red litmus paper to blue Reacts with acids to form salt and water Ex: soap, shampoo, cleaning agent Arrhenius Theory By Svante August Arrhenius Acids form hydrogen ion(H+) in aqueous solutions Bases form hydroxide ion (OH-) in aqueos solution Ex: HCl(g)-----> H+(aq) + Cl-(aq) KOH -----> K+ + OH-(aq) Bronsted-Lowry Denition By Johannes Bronsted and Thomas Lowry Acid is a proton donor Base is a proton acceptor Ex: HCl + H2O ---> H3O + ClNH3 + H2O Bronsted-Lowry Definition The general reaction when an acid is dissolved in water is best represented by an acid donating H+ to water molecule to form a new acid (conjugate acid) and a new base( conjugate base) acid Acid base base conjugate Conjugate HA(aq) + H20(l) ----> H3O+(aq) + A-(aq) Ex: HCl + H2O ---> H3O+ + acid base conjugate acid Clconjugate base . Practice: Identify the acid and the base in the following reactions: HSO4- + PO43- ---> HPO42- + SO42HNO3 + H2O ---> H3O + + NO3H3PO4 + CN- ---> H2PO4- + HCN Conjugate Acid-base pair Consists of two substances related to each other by donating and accepting of a single proton Acid-conjugate base pair Ex: HCl(aq) + H2O(l) H3O+ + ClBase-conjugate acid pair H3O+ --> hydronium ion Strong Acids Bronsted-Lowry definition is useful in describing the strength of an acid Strong acid is one that dissociates or ionizes completely in water Ex:HCl + H2O H3O+ + ClForward reaction predominates which indicates ionization is complete Strong acid contains a weak conjugate base weaker than water Weak Acid It does not completely dissociate or ionize. Ex: Acetic Acid( CH3COOH) CH3COOH + H2O H30+ + CH3COOacetate ion The two arrows indicate that the ionization is not complete The reverse reaction predominates that means only few ions are dissociated Weak acid contains relatively strong conjugate base Strong Bases Common strong bases are those that contain the hydroxide ion Ex:,NaOH,KOH Mg(OH)2, Ca(OH)2 Ba(OH)2 Very soluble in water Weak Bases The strengths of bases that do not have OH- are described in the same way that the strengths of the acids were described Weak base does not completely dissociate in water Ex: NH3 + H2O NH4+ + OHreverse reaction predominates Acid Strength Strong Acid Strong Base Moderate Acid Weak Acid Weak Base HClO4 NaOH H3PO4 CH3COOH NH3 HClO3 KOH Moderate Base H2CO3 HCO3- HI Mg(OH)2 CO32- H3BO3 CH3COO- HBr Ca(OH)2 CH3COOH SO42- Ba(OH)2 Sulfuric acid Very Weak Acid Very Weak Base HCl H2O H2O Perchloric acid Phosphoric acid Chloric Acid Hydrobromic H2SO4 Hydrochloric HNO3 Nitric Acid Water as an acid and a base Amphoteric substance A substance that can behave either as an acid or a base Ionizaton of water H2O(l) + H2O(l) ---> H3O+(aq) + OH-(aq) The forward reaction is not great In pure water only a tiny amount of H3O+ and OH- is present. [H3O+] = [OH-] = 1.0x10-7M The product of the H3O+ and OH- concentrations is always constant at 250C [H3O] [OH-] = 1x 10 -14 (1x 10-7 ) ( 1 x 10-7) = 1 x 10-14 This is called the ion product constant of water ( Kw) Note the product of H3O and OH- in any aqueous is constant which means when [OH-] goes up the [H3O] must go down Acidic solution [H+] > [OH-] Basic solution [ H+] < [OH-] Neutral solution [H+] = [OH-] Ex : calculate [H+] or [OH-] as required for each of the following at 250C and state whether the solution is acidic, basic and neutral A) 1.0x10-5M OHGiven: [OH-] = 1x10-5 Find: H+ Solution: [H+] [OH-] = 1x10-14 [H+] = 1x10-14 [OH-] [H+] = 1 x 10-14 [ 1x10-5] = 1x 10-9 M Since OH- = 1x10-5M H+ = 1x10-9M The solution is basic since OH- > H+ b) 10.0M H+ Find: OHSolution: [H+][OH-] = 1 x10-14 [OH-] = 1x 10-14 10.0M = 1x 10-15M [OH-] = 1x10-15 [H+] = 1x 101M [H+] > [OH-] = the solution is acidic The pH Scale Was proposed by Soren Sorensen ( Danish biochemist) pH means power of hydrogen Has a range from 0 to 14 and is logarithmic which means that each step is ten times the previous Ex: pH of 5 is ten times more acid than 6 What about pH 5 and 7 ---> pH 5 is 100times more acid than 7 What about pH 5 and 8? 1000 times acidic pH scale 0-most acidic and 14 is most basic 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 At pH-7, water has equal amount of H+ and OH- ions [H+] = [OH-] neutral [H+] > [OH-] acidic [H+] < [OH-] basic pH of a solution Defined is the negative of the logarithm of the hydronium ion concentration, [H3O+] pH = - log [H3O+] Ex: Pure water has [H3O+]= 1x10-7M. Find pH pH = -log[H3O+] pH = -log[ 1x10-7M] pH = - (-7) pH = 7 In Basic solution, [OH-] can be expressed as pOH pOH = -log [OH-] Recall that [H3O+] [OH-] = 1 x 10 -14 Using the definition of pH and pOH the equation can be translated as pH + pOH = 14 In summary, pH= -log[H3O+] pOH = -log [OH-] [H3O+][OH-] = 1x10-14 pH + pOH = 14 Ex: Find the pH and pOH of 0.001MHCl solution Given: [H3O+] = 0.001M Find a) pH b) pOH Solution A) pH = -log [H3O+] = -log [ 1x10-3] = -(-3) =3 B) pH + pOH = 14 pOH = 14 - pH = 14 - 3 11 Ex2: If the OH- is equal to 0.00001M, Find the pH Solution: Get the pOH first pOH=-log[OH-] = -log(10-5M) = -(-5) pOH = 5 Get the pH pH +pOH = 14 pH = 14 – pOH = 14 – 5 pH = 9 Indicators Substances that exhibit different colors in acidic and basic solutions. It has a weak acid(conjugate acid) has a color, and its conjugate base has another color HInd(aq) + H2O H3O+ + IndConjugate acid conjugate base Are usually used in solutions like phenolphthalein while others used in a form of strips called pH paper , and litmus paper Phenolphthalein: in acid colorless in base pink Some Indicators Indicator pH interval color Color change phenolpthalein 8.3 - 10 Colorless - pink Methyl orange 3.1 – 4.4 Red - yellow Bromcresol green 3.8 – 5.4 yellow- blue Phenol red 6.4 – 8.2 yellow- red Thymolpthalein 9.4 to 10.6 Colorless- blue Litmus paper 4.5 – 8.2 Red to blue Buffer Solution One that contains a weak acid and its conjugate base, or a weak base and its conjugate acid Has a remarkable property of maintaining an constant pH even though a strong acid or a base is added to the solution The pH of biological fluids is maintained by buffers. Ex: blood is heavily buffered by Note: Buffers has a remarkable property of maintaining an almost constant pH even with the addition of a strong base or acid due to the presence of the weak acid that neutralizes any added base and also a weak base that neutralizes any added acid. Example A solution with 1.0M CH3COOH(acetic acid), and 1.0M in NaCH3COO( sodium acetate)base. The acid will react with any added base as follows: CH3COOH + OH- ---> H2O + CH3COO The base will react with any added acid (H3O+) CH3COO- + H3O+ H2O + CH3COOH Neutralization Reaction occurs between an acid and a base producing equal amounts of H3O+ and OHChemical reaction that forms water and salt Occurs between Strong acid and strong base A weak acid and a strong base A weak acid and a weak base Neutralization Occurs when an equivalent amount of an acid reacts with an equivalent amount of a base HCl + NaOH ----> NaCl + H2O neutral solution This process is accomplished by means of titration Neutralization Reaction Acid and base properties combine to form water H+ + OH- -------> H2O Note: water is one of the products of neutralization reaction Acid Base Titration Is a useful application of neutralization reaction A process of adding a solution of accurately known concentration, standard solution, ( titrant) to another solution of unknown concentration,( analyte until the chemical reaction between the two is complete ( the equivalence point) or end point Equivalence point is the point in titration where the indicator used undergoes a color change Note; indicator changes color at pH=7 At the equivalence point, n Acid = n base, to get the molarity of the base or acid M = n = moles V L M acid = n acid V acid , nA = n B MAVA = MBVB M base = n bas Vbase Ex: In a titration, It takes 6mL of 0.5MNaOH to neutralize 15mL of HCl. What is the concentration of HCl? NaOH + HCl -----> NaCl + H2O molar ratio ( 1:1) MA VA = MBVB MA = MBVB = (0.500M)(6mL) VA 15mL = 0.2M Sample 2 A 25.0mL of sulfuric acid solution requires 32.58mL of .500M NaOH to neutralize it. What is the molarity of H2SO4? Solution: 1.Write the balance equation H2SO4 + NaOH ---> H2SO4 + NaOH ---> Na2SO4 + H2O H2SO4 + 2 NaOH ---> Na2SO4 + 2 H2O 2mole NaOH : 1 mole H2SO4 2.Determine the number of moles of NaOH M = n , n = MV n = (0.500moles) ( 0.03258L) = 0.01629 moles V L 3.Determine the molarity of H2SO4 using nA = nB M = n , M = 0.01629moles NaOH x 1mole H2SO4 V 0.025L 2mole NaOH M H2SO4 = 0.3258M