Chapter 18 Acids and Bases

Properties of Acids and Bases Physical properties: Acids: taste sour, conduct electricity Bases: taste bitter, feel slippery, conduct electricity

Chemical properties Acids: turn litmus paper red Bases: turn litmus paper blue

The Arrhenius Model Acids – produce hydrogen ions in aqueous solution HCl H+ + Cl- Bases – produce hydroxide ions in aqueous solution NaOH  Na+ + OH-

The Bronsted-Lowry Model Arrhenius concept is limited because it only allows for one kind of base Acid – proton donor Base – proton acceptor

General reaction for a Bronsted-Lowry acid dissolving in water: Conjugate acid-base pair – two substance related to each other by the donating and accepting of a single proton

Identify the acid, base, conjugate acid, and conjugate base in the following: HCO3 -1 + H2O  CO3 -2 + H3O +1

Water as an Acid and a Base Amphoteric substance – can behave either as an acid or as a base Ionization of water: One water molecule acts as an acid donating protons, one acts as a base accepting protons

Strengths of Acids and Bases Strong acids and bases ionize completely Weak acids and bases ionize only partially

A strong acid contains a relatively weak conjugate base, one that has a low attraction for protons A weak acid contains a relatively strong conjugate base

Hydrogen and Hydroxide Ions and pH Acidity or Basicity of a substance is related to the concentration of hydrogen and hydroxide ions in that substance

The product of [H+] and [OH-] is always constant Kw = ion product constant for water No matter what the solution contains, Kw will always equal 1.0 x 10-14

Calculate the [H+] or [OH] and state whether the solution is neutral, acidic, or basic 1.0 x 10-5 M OH- 1.0 x 10-7 M OH- 10.0 M H+

Determining the Acidity of a Solution The pH Scale: 0 – 14 <7 = acidic 7 = neutral >7 = basic

A mathematical scale in which the concentration of H+ ions in a solution is expressed as a number from 0 – 14 pH = log [H+]

What is the pH of solutions having the following ion concentrations? [H+] = 1.0 x 10-2 M [H+] = 3.0 x 10-6 M

Because the pH scale is a log scale based on 10, the pH changes by 1 for every power of 10 change in the [H+]

Log scales similar to the pH scale are used for representing other quantities: pOH = log [OH]

What is the pOH of a solution having the following ion concentration? [OH-] = 1.0 x 10-6 M [OH-] = 6.5 x 10-4 M

pH + pOH = 14 What is the pOH of a solution whose pH is 5? What is the pH of a solution whose [OH-] = 4.0 x 10-3 M

Calculate the pH and pOH of the following solutions: [H+] = 0.000033 M [OH-] = 0.0095 M

It is also possible to find the [H+] or [OH-] from the pH or pOH by undoing the log operation [H+]= 10-pH [OH-] = 10-pOH

The pH of a human blood sample was measured to be 7. 41 The pH of a human blood sample was measured to be 7.41. What is the [H+] and [OH-]in this blood?

Neautralization Reactions Acid + Base  salt + water HCl + NaOH  NaCl + H2O Ionic: Net ionic:

Titration Method for determining the concentration of a solution by reacting a known volume of that solution with a solution of known concentration. If unknown is acid, known must be base

Titration procedure Measured volume of acid or base of unknown concentration is placed in a flask and initial pH is recorded Buret is filled with the solution of known concentration (standard solution/titrant) Standard solution added slowly until neutral pH is reached (equivalence point) [H+] = [OH-]

End point of a titration can be measured using a pH meter or an indicator Indicator changes color at different pH values

Titration curve (pH curve) – plot of pH vs volume of titrant added

A volume of 18. 28 mL of a standard soluiton of 0 A volume of 18.28 mL of a standard soluiton of 0.1000M NaOH was required to neutralize 25.00 mL of a solution of nitric acid. What is the concentration of the nitric acid?

Buffered Solutions Solutions that resist changes in pH when acids or bases are added Weak acid + conjugate base HF + NaF