2Properties of Acids They are corrosive pH range is 0 to 7, lower the pH, more acidic the acidTaste sourTurns litmus paper redOften reacts with metals to produce H2 gasOften produces H+ in water. Example; HCl H+ + Cl-
4Properties of BasespH range is from 7 to 14, higher the pH more alkaline the baseThey are causticTaste bitterTurns litmus paper blueFeels slipperyGroup 1 and 2 metals make common bases. Example: Na + H2O NaOH + 1/2H2
6Common Acids Binary or Halide Acids HCl, hydrochloric acid: is stomach and pool acidHF, hydrofluoric acid: used to etch glass
7Common acids continued Oxyacids: acids with oxygen (more oxygen- stronger the acid)HNO3, Nitric acid, used for making explosives, when it reacts with metals it produces NO2gas instead of H2H2SO4, sulfuric acid: used in car batteries, used in many industrial process as a dehydrator.
10Oxyacids continuedH2CO3, carbonic acid, found in carbonated sodas, and in rainwater. It is responsible for the sour taste, or sting in sodas. It is also found in blood to a very small extent.H3PO4, phosphoric acid, used as lime scale remover, and as flavoring in the colorless sodas like Sprite.
11Acids continued Organic acids Carbon based acids. Structure ends in COOHCOOH is called a carboxyl group.CH3COOH, ethanoic acid or vinegar. Used as a preservative and flavoringOC-OH
12Bases Group 1 bases Group 2 bases Strongest bases NaOH, sodium hydroxide, and KOH, potassium hydroxide, both of these bases are used to make commercial cleansers and drain cleaners.Group 2 basesWeak bases,Ca(OH)2 calcium hydroxide, make limewater which is used to test for CO2,,used to make antacids.
13Bases Amines. This group has a -NH2 at the end of a molecule These are formed from decomposing proteinsThey have a “fishy” smellNH3, ammonia, this is used as glass cleaner and to make fertilizers.Examples CH3NH2, methyl amine, CH3CH2NH2 ethyl amine. Etc.
15Bases Carbonates (they are antacids) Have CO3 -2 in them This group produces CO2 when they react with acids.NaHCO3 sodium bicarbonate, or baking sodaCaCO3, calcium carbonate, or baking powder.MgCO3 and Al2(CO3)3 are used as antacids, for example: MgCO3 + 2HCl MgCl2(aq) + H2O(l) + CO2(g)
16Arrhenius definition of acids and bases Acids produce a hydrogen ion(H+) or hydronium ion (H3O+) when they dissolve in water. (An H+ ion is considered too reactive to exist so an H3O+ ion is used)Acids dissolving in water producing an H+HCl H+ + Cl-HNO3 H+ + NO3-H2SO4 2H+ + SO4-2CH3COOH CH3COO- + H+
18Arrhenius definition continued Acids dissolving in water form a hydronium ion:HCl + H2O H3O+ + Cl-HNO3 + H2O H3O+ + NO3-H2SO4 + 2H2O 2H3O+ + SO4-2CH3COOH + H2O CH3COO- + H3O+Note: H2O is written in the reaction when H3O+ is used, but not when H+ is used.
20Arrhenius definition of bases Bases dissolve in water to produce an OH- called a hydroxide ion.NaOH Na+ + OH-Ca(OH)2 Ca+2 + 2OH-NH3 + H2O NH4+ + OH-Note: H2O is written in the reaction only with amines
21Bronsted-Lowry def. of Acids/Bases Acids are proton donorsBases are proton acceptorsEx: HNO2 + H2O H3O+ +NO2-Ex: NH3+ HCO3- NH4+ + CO3-2Ex: HCO HSO4- SO4-2 + H2CO3
22Determining the conj. Acid of a base --Add a H+Base Conj. AcidHCO3- H2CO3H2O H3O+OH- H2O
23Determining the conjugate base of an acid. --remove an H+Acid Conj. BaseH2O OH-HSO4- SO4-2NH4+ NH3
24Continued Bronsted-Lowry Stronger the acid/ base, the weaker its conjugate base/ acid.Amphoteric or Amphiprotic: A substance which can be either an acid or a base.Example is H2O.Water as an acid: H2O + Cl- OH- + HClWater as a base: H2O + HCl H3O+ + Cl-
26Definition of a Lewis acid and base Acids are electron pair acceptors in a dative covalent bond.Bases are electron pair donors in a dative covalent bond.These acids are reserved for those molecules/ions which make dative covalent bonds but are NOT ALREADY A BRONSTED-LOWRY ACID.Examples: NH3 is a base because the nitrogen has a pair of electrons which can be used in a dative bond. AlF3 can be a Lewis acid since Al has a vacant pair of orbitals that can accept e-.
27Lewis acids will include substances that are not considered typical acids. Examples:Some metal ions. Ex Group 3, Trans. metals
28Strong acids and bases completely dissociate in water
29Strong and weak acids and bases Strong acid/base when it dissolves in H2O, nearly 100% dissociates into ions.Ex: HCl H+ + Cl- nearly 100% of the molecules break up into ionsEx: NaOH Na+ + OH- nearly 100% of the molecules break up(Remember: the H+ and OH- gives the properties associated with Acids and Bases.)▪ For weak acid and bases, when they dissolve in water only a small % will dissociate to form ions.CH3COOH(aq) CH3COO- (aq)+ H+(aq) Very little of the acid forms ions. Same condition for weak bases.▪ Both the strength and the concentration of the acid or base determines its pH and its harmfulness. So when working with acids and bases one needs to be concerned with1. Is the acid or base strong or weak?2. Is the acid or base concentrated or dilute?
32The pH equation The pH equation is: pH = -log [H+] Where [H+] is the molar concentration.
33The pH scale Development of the pH scale Based upon the dissociation of water: H2O H+ + OH-Based upon the equilibrium of water: Kw = [H+] [OH-]at equilibrium the concentrations of H+ and OH- are each 1x10-7M (this was experimentally determined)Substitute these concentrations into the Kw expression: Kw = [1x10-7][1x10-7]; this = 1x10-14
34Development of the pH scale cont. According to the rules of equilibrium changing conc does not change the Kw constant. So if acid is added to water, the H+ conc goes up, and the OH- goes down, but K equals 1x The same thing happens if a base is added to water. Knowing that Kw is always 1x10-14, thenThe largest conc for either an H+ or OH – is 1MThe smallest conc H+ or OH – is 1x10-14 that we work withthe –log of 1M = 0 the low end of the pH scalethe –log of 1x10-14 = 14 the high end of the pH scaleAlso, pure H2O has a conc of H+ = 1x10-7, the –log = 7, pure H2O has a pH of 7 or it is neutral
38Explanation of a titration curve A titration involves an acid base reaction:Example NaOH + HCl NaCl + NaOHAll titration curves have the same shape but they do not all start at the same pHWhy this shape?Start with 1M HCl titrated with 1M NaOHInitial pH=O, titrate 10% of 1MHCl, 90% of HCl remains. [H+]= .9M or pH= .05Titrate 50% of 1M HCl, 50% remains [H+]= .5M or pH= .3 (not a great change in pH yet!)Titrate 90% of 1MHCl , 10% remains, [H+]=.1M or pH=1Titrate 100% of HCl, acid and bases are now equal, pH=7 the cure shoots up until excess NaOH is added. Now curve gradually increases again with the addition of more NaOH
42IB optional material: Equilibrium and weak acids and bases Since weak acids and bases disassociate partially:They are reversible and have a measurable equilibrium.Their pH cannot be based upon the initial molarity of the acid or base. An equilibrium equation must be used to measure it.
43The Ka or Kb (equilibrium constant) of weak acids or bases