2Acids and BasesSome of our favorite foods make our tongue curl up because they are SOUR.
3Bitter!Some foods have a “bite” of their own because they’re somewhat bitter.WHY?
4Acidic/Basic There is a scientific reason for this: These foods are either acidic or basic.Other substances besides foods have these characteristics.
5Acids and Bases Chemicals may be classed as acids or bases. Things that are neither acids nor bases are neutral.pH measures how acidic or basic a solution is.
6Acids Often taste sour Strong acids can burn skin & eyes Strong acids can dissolve metalsExamples:Lemon juiceVinegarCar battery acid (dangerous!)
7Bases Can taste bitter, sweetish, or salty Strong bases can burn skin & eyesBases react more easily with protein than with metal; they are often used for cleaningExamples:MilkBaking sodaSoapDrain cleaner (dangerous!)
8Some substances are not really an acid or a base: For example, pure water
9The Nomenclature ofACIDSAcids are easy to recognize as compounds as they begin with the element hydrogen. As with other ionic bonds, acids fall into 2 categories, binary and ternary.
10The Nomenclature ofACIDSExamples of binary acids would include things like:HF, HI, H2S and HClExamples of ternary acids would include things like:H2SO4 and HNO3
11The Nomenclature ofACIDSNaming of binary acidsStep 1:Name the anion, changing the ending to “-ic”Step 2: Add the prefix “hydro-”Step 3: Slap acid on the end
12“hydroflouric acid” The Nomenclature of ACIDS Example #1: HF “fluorine” becomes“fluoric” becomes“hydrofluoric” becomes“hydroflouric acid”
13Naming of ternary acids The Nomenclature ofACIDSNaming of ternary acidsStep 1:Name the polyatomicStep 2: Change “-ate” to “-ic”or “-ite” to “-ous”Step 3: Slap acid on the end
14“sulfuric acid” The Nomenclature of ACIDS Example #1: H2SO4 “sulfate” becomes“sulfuric” becomes“sulfuric acid”
15Rules for Writing Formulas for binary acids The Nomenclature ofACIDSRules for Writing Formulas for binary acidsStep 1: Does the name begin with“hydro-”? If yes, then…Step 2:Write the symbol for thehydrogen ion followed by thesymbol for the second elementStep 3: Crisscross the charges and write them as subscripts.
16The Nomenclature of ACIDS Rules for Writing Formulas for binary acidsExample: hydrosulfuric acid
17The Nomenclature of ACIDS Rules for Writing Formulas for binary acidsExample: hydrosulfuric acidH S-2
18The Nomenclature of ACIDS Rules for Writing Formulas for binary acidsExample: hydrosulfuric acidH S-2
19H2S The Nomenclature of ACIDS Example: hydrosulfuric acid H+1 S-2 Rules for Writing Formulas for binary acidsExample: hydrosulfuric acidH S-2H2S
20Rules for Writing Formulas for ternary acids The Nomenclature ofACIDSRules for Writing Formulas for ternary acidsStep 1: Does the name begin with“hydro-”? If no, then…Step 2:Write the symbol for thehydrogen ion followed by theappropriate polyatomic ionStep 3: Crisscross the charges and write them as subscripts.
21Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature ofACIDSRules for Writing Formulas for binary acidsExample: sulfuric acid
22Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature ofACIDSRules for Writing Formulas for binary acidsExample: sulfuric acidH SO4-2
23Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature ofACIDSRules for Writing Formulas for binary acidsExample: sulfuric acidH+1 SO4-2H+1 SO4-2
24Rules for Writing Formulas for binary acids Example: sulfuric acid The Nomenclature ofACIDSRules for Writing Formulas for binary acidsExample: sulfuric acidH+1 SO4-2H+1 SO4-2H2SO4
25The Nomenclature of ACIDS Name the chemical or write the symbol1. HI2. phosphoric acid3. hydrobromic acid4. H2SO3
26The Nomenclature of ACIDS Name the chemical or write the symbolhydroiodic acid1.2. phosphoric acid3. hydrobromic acid4. H2SO3
27The Nomenclature of ACIDS Name the chemical or write the symbolhydroiodic acid1.2.3. hydrobromic acid4. H2SO3H3PO4
28The Nomenclature of ACIDS Name the chemical or write the symbolhydroiodic acid126.96.36.199. H2SO3H3PO4HBr
29The Nomenclature of ACIDS Name the chemical or write the symbolhydroiodic acid188.8.131.52.H3PO4HBrsulfurous acid
30pH Scale We use this scale to measure the strength of an acid or base. pH is defined as the –log[H+]pH can use the concentration of hydronium ions or hydrogen ions.
317AcidBasepH Scale14Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515
32pH of Common Substances Timberlake, Chemistry 7th Edition, page 335
33The pH Scale pH scale ranges from 0 -14 pH 7 is neutral; neither acid nor basePure water is pH 7Low pH (0-6.9) = acidHigh pH (7.1-14) = baseThe closer to the ends of the scale, the stronger the solution is
340--------------7---------------14 AcidAny substance which has a pH of value of less than 7 is considered an acidAcid Neutral Base
350--------------7---------------14 BaseAny substance which has pH value greater than 7 is a baseAcid Neutral Base
36pH 7 A pH of 7 is called neutral—neither acid nor base. Acid Neutral Base
37The pH Scale Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidicx10x100
38The pH Scale Careful measurement is important A mistake of one pH unit means 10 times too much or too little!x10x100
39How Do We Measure pH?One way to measure pH is by using special strips of paper called pH paper
40How Does It Work?The paper is treated with chemicals (indicators) that change color to show the pH.When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base.
41To Use pH Paper Place the edge of the pH paper into the mixture. Observe the color change of the pH paperMatch the resulting color to the colors listed on the outside of the pH paper package.The colors match with a correlated pH number.The number is the pH value of the sample.
42Historical views on acids The Oldest Theory is the Arrhenius Theory
43Arrhenius looked at the substances which were called acids Arrhenius looked at the substances which were called acids. Some of these substances were known from even before the days of alchemy.They taste sour, turn blue litmus to red, neutralize bases, release hydrogen gas when added to an active metal and release carbon dioxide when added to a carbonate.Arrhenius said these properties were due to the production of H+ ions when acids dissolve in water.
44He looked at the properties of bases He looked at the properties of bases. They taste bitter, feel slippery (soapy), turn red litmus blue and neutralize acids.Arrhenius said these properties were due to the production of OH- ions when bases are dissolved in water.
45Historical views on acids O2 found in oxyacids (e.g. H2SO4) was originally thought to cause acidic properties. Later, H2 was implicated, but it was still not clear why CH4 was neutral.Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H2+ ions in solution.+HOHOClClH++Ionization
46Historical views on acids The more recent Bronsted-Lowry concept is that acids are H+ (proton) donors and bases are proton acceptors+HOHOClClH++
47The Bronsted-Lowry concept In this idea, the ionization of an acid by water is just one example of an acid-base reaction.+ClHOacidbaseconjugate acidconjugate baseconjugate acid-base pairsAcids and bases are identified based on whether they donate or accept H+.“Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H+.
48The Bronsted-Lowry concept Today we know that a bare proton does not exist in water, it forms a chemical bond with a water molecule forming the H3O+. This ion is called the hydronium ion.H2O H3O+ + OH-“Pure” water is always a dynamic mixtureof these three substances in equilibrium
49The Bronsted-Lowry concept 1) A B/L acid is the species which donates a proton in a proton transfer reaction. What is meant by a proton here?2) A B/L base is the species which _________ .3) A B/L acid is the species which _________
50HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq) 4) A specific strong acid - base reaction:HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)HCl(aq) is the ___________________ .H2O(l) is the ________________ .H3O+(aq) is the ________________________.Cl-(aq) is the _________________________ .
51CH3COOH is the _____________________. H2O is the _________________________.H3O+ is the ____________________.CH3COO- is the _____________________.
55Reaction Types HCl + NaOH NaCl + H2O HCl + NaOH NaCl + H2O Neutralization Reaction – a special double replacement reaction in which an acid is combined with a base and yields water and a salt.HCl + NaOH NaCl + H2OHCl + NaOH NaCl + H2O
56TitrationsIn a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete.End point – the point at which the reaction becomes completeEquivalence point – the point at which the reaction is neutralIndicator – substance that changes color at (or near) theequivalence pointSlowly add baseto unknown acidUNTIL the indicatorchanges color4.7
57Ma x Va = Mb x Vb What volume of a 1.420 M NaOH solution is Required to titrate mL of a 4.50 M H2SO4solution?WRITE THE CHEMICAL EQUATION!H2SO4 + 2NaOH H2O + Na2SO4Ma x Va = Mb x Vb