1 Acids and Bases Chapter 20-1
2 Describing Acids and BasesObjectives List the properties of acids and bases. Name an acid or base, when given the formula.
3 Describing Acids and BasesArrhenius Definitions Acid A substance that produces hydrogen ions in aqueous solutions. Base A substance that produces hydroxide ions in aqueous solutions.
4 Properties of Acids Acids Taste sour (don’t try this at home).Conduct electricity. Some are strong, some are weak electrolytes. React with metals to form Hydrogen gas
5 Properties of Acids Acids Change the indicatorsBlue litmus paper to red. 5. React with Bases to form water and salt.
6 Properties of Bases Bases or Alkalis Taste bitter.Conduct electricity. Can be strong or weak electrolytes. Feel slippery. Change indicators. Red litmus paper to blue React with acids to form water and salt.
7 Names and Formulas of AcidsAn Acid is a compound that produces Hydrogen ions when dissolved in water. General form of Chemical formulas: HX Where X is a monatomic or polyatomic anion. Anion ending Example Acid Name -ide S-2 Hydro-(stem)-ic acid Hydro sulfuric H2S -ite SO3-2 (stem)-ous Sulfurous acid H2SO3 -ate SO4-2 (stem)-ic Sulfuric acid H2SO4
8 Names and Formulas of BasesA base is a compound that produces hydroxide ions when dissolved in water. Bases are named in the same way as any other ionic compound. Name of the cation followed by the name of the anion. Al(OH)3 Aluminum hydroxide KOH Potassium hydroxide
9 Hydrogen Ions and AcidityChapter 20-2
10 Hydrogen ions and AcidityObjectives Given the hydrogen-ion or hydroxide-ion concentration, classify a solution as neutral, acidic, or basic. Convert hydrogen-ion concentrations into values of pH, and hydroxide-ion concentrations into values of pOH.
11 Hydrogen Ions from WaterWater ionizes, or falls apart into ions: The reaction in which two water molecules produce ions is called the self-ionization of water H2O(l) ® H1+(aq) + OH1-(aq) In water or aqueous solutions, hydrogen ions are always joined to water molecules as hydronium ions (H3O+1)
12 A water molecule that loses a hydrogen ion becomes a negative charged hydroxide ion.OH1- A water molecule that gains a hydrogen ion becomes a positive charged Hydronium ion H3O+1 Hydrogen ions = protons = hydronium ions H2O(l) ® H1+(aq) + OH1-(aq) Hydrogen ions in aqueous solutions have several names
13 The self ionization of water occurs to a very small extent. In pure water at 25 0C, the concentration of hydrogen ions and the concentration of hydroxide ions are each only 1.0 x 10-7. Any aqueous solutions in which [H+] and [OH-] are equal is described as a neutral solution. [H+] = [OH-] = 1.0 x 10-7 Neutral solutions
14 In an aqueous solution, [H+] and [OH-] are interdependentIon-product constant for water (Kw) When [H+] increases, [OH-] decreases When [H+] decreases, [OH-] increases For aqueous solutions, [H+] x [OH-] = 1.0 x 10-14 Kw = [H+] x [OH-] = 1.0 x 10-14
15 Acidic solutions Basic solution (alkaline solution) An acidic solution is one in which [H+] is greater than [OH-] [H+] > 1.0 x 10-7 A basic solution is one in which [H+] is less than [OH-] [H+] < 1.0 x 10-7
16 Sample Problems If the [H+] in a solution is 1.0 x 10-5 M, is the solution acidic, basic, or neutral? What is the [OH-] of this solution? If the [H+] in a solution is 6.0 x M, is the solution acidic, basic, or neutral? What is the [OH-] of this solution?
17 The pH Scale It is used to express the [H+]The pH scale is a log scale based on 10. The pH changes by 1 for every power-of-10 change in the [H+]. A solution with a pH of 3 has 10 x the [H+] than a pH 4 and a 100 x the [H+] of a pH 5
18 The pH Scale Mathematical expression of pHThe scale range is from 0 to 14. The pH of a solution is the negative logarithm of the hydrogen-ion concentration. pH = -log [H+] pH = 7 ; neutral solution pH > 7 ; basic solution pH < 7 ; acidic solution
19 The pOH of a solution equals the negative logarithm of the hydroxide-ion concentration.pOH = -log [OH-] pOH = 7 ; neutral solution. pH + pOH = 14
20 Sample Problems What is the pH of a solution with a hydrogen-ion concentration of 1.0 x M? What is the [H+] of a solution if the pH is 3.70? Find the pH of a solution if the [OH-] is 2.5 x 10-3 M. What is the hydroxide-ion concentration from a solution with a pH of 6?
21 Measuring pH pH is measured to find out the correct acid-base balance in a swimming pool, to creating soil conditions ideal for plant growth, to making medical diagnosis. To make precise and continuous measurements a pH meter is needed. The pH meter is an accurate tool. Indicator strips is another common tool to find the pH of a solution Another method to find the pH of a solution is by using Acid-Base indicators.
22 Measuring pH Acid-Base indicators are weak acids or bases that undergoes dissociation in a known pH range. Weakness of Acid-Base indicators: The pH values of indicators are usually given for 25 0C. If the solution is not colorless, the color of the indicator may be distorted. Dissolved salts in a solution may also affect the indicator’s dissociation.
23 Acid-Base Theories Chapter 20-3
24 Arrhenius Acids and BasesMonoprotic Acids are hydrogen-containing compounds that ionize to yield Hydrogen ions (H+) Acids that contain one ionizable hydrogen HNO3 HCl
25 Arrhenius Acids and BasesDiprotic acid Triprotic acid Acids that contain two ionizable hydrogens. H2SO H2CO3 Acids that contain three ionizable hydrogens. H3PO4
26 Arrhenius Acids and BasesNot all compounds that contain hydrogen are acids. Only hydrogens in very polar bonds may be released as hydrogen ions Only the hydrogens in very polar bonds are ionizable.
27 Arrhenius Acids and BasesA compound that produces hydroxide ions when dissolved in water. NaOH, commonly known as lye, is a compound that is very caustic. Can cause deep, painful, slow-healing wounds if not immediately washed off. Bases
28 Arrhenius Acids and BasesSodium and Potassium are Group 1A elements. They react with water to produce alkaline solutions. Both NaOH and KOH are very soluble in water. On the other hand, elements on Group 2A are not very soluble in water. Consequently their solutions are very dilute. They contain very low [OH-]. People take these suspensions internally as milk of magnesia (antacid and a mild laxative. Bases
29 The Brønsted-Lowry TheoryAlthough the Arrhenius concept of acids and bases was a major step forward in understanding acid-base chemistry, this concept is limited because it applies only to aqueous solutions and allows for only one kind of base- the hydroxide ion (OH-).
30 The Brønsted-Lowry TheoryDefinition of an acid Definition of a base An acid is a proton donor. A base is a proton acceptor. All acids and bases using the Arrhenius theory are acids and bases under the Brønsted-Lowry Theory
31 The Brønsted-Lowry TheoryThe behavior of NH3 as a base can be understood by using the Brønsted-Lowry Theory The NH3 gas is very soluble in water. When NH3 dissolves in water, it acts as a base because it accepts a H+ from H2O. NH3 + H2O NH4+ + OH-
32 The Brønsted-Lowry TheoryWith the Brønsted-Lowry Theory a conjugate acid and a conjugate base are formed. A conjugate base is a particle that remains when an acid has donated a hydrogen ion. A conjugate acid is a particle formed when a base gains a hydrogen ion. Conjugate acids and bases are always paired with a base or an acid.
33 The Brønsted-Lowry TheoryConjugate acid and base. HCl + H2O H3O Cl-
34 The Brønsted-Lowry TheoryAny neutral solution can act as both an acid and a base. A substance that can act as both an acid and a base is said to be amphoteric. Water is amphoteric.
35 Lewis Acids and Bases A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. A Lewis base is a substance that can donate a pair of electrons to form a covalent bond.
36 electron pair acceptorAcid Base Definitions Type Acid Base Arrhenius H+ producer OH- producer Brønsted-Lowry H+ donor H+ acceptor Lewis electron pair acceptor Electron pair donor