Chapter 18

Acids and Bases

Rainbow Connection#2

Ch. 18- Acids and Bases

• Acids and bases have a central role in chemistry

• They affect our daily life• Uses: manufacturing processes,

environmental issues, functioning of our bodies

• Acid/ Base Video

Properties of Acids

• Have pH 0-6• Tart or sour taste• Will conduct electricity• Cause indicators to change color (turns

blue litmus red)

• Reacts w/ metals (Mg,Zn) to form H2 gas

• Neutralize w/ a base forms a salt and H20

• Ex. Citrus foods, tomatoes, vinegar

Acid Formulas (memorize)

• HCl ( Hydrochloric Acid)

• HNO3 (nitric acid)

• H2SO4 (sulfuric acid)

• H2CO3 (carbonic acid)

• HC2H3O2 (acetic acid)

• H3PO4 (phosphoric acid)

Properties of Bases

• Also known as alkaline• pH 8-14• Have a bitter taste, slippery feel• Causes indicators to change color (turns

red litmus blue)• Conducts electricity• Reacts w/ acid to neutralize form a

salt and H2O• Ex. Cleaning products, soap, baking soda

Acid/ Base Theories

• Definitions have changed over the years as new information has been found

• Arrhenius Theory video

Arrhenius Theory (1887)

• Applies to a H2O solution• Svante Arrhenius (Swedish) saw that not

only do acids/ bases conduct electricity, they ionize (or release charged particles) when dissolved in water

• Theory:1. Acids- substance that ionize & produced (H+)

hydrogen ions in H2O2. Bases- ionize to produce (OH-) hydroxide

ions in H2O

Ex. HCl H+(aq) + Cl-(aq)

ACID

NaOH Na+(aq) + OH-

(aq)

BASE

Brønsted- Lowry Theory (1923) (video)

• Working independently of each other, Johannes Brønsted (Danish) and Thomas Lowry (English) defined a theory that can be used w/ all solvents not just H2O (they found that substance lost or gained protons)

• Acid- in a chemical reaction, this is the substance that loses or donates a proton (H+ ion)

• Base- substance that accepts or gains a proton (H+ ion = proton)

• HCl + H2O H3O+ + Cl-

Accepts proton (base)

Donates (loses) proton – (acid)

H3O+ hydronium ion (formed when H2O gains H+ ion)

• NH3 + H2O NH4+ + OH-

Accepts proton (base)

Donates (loses) proton – (acid)

Amphoteric – (H2O) acts as an acid or a base (depending on the situation)

Conjugates

• The particles that are formed as products can react again (reversible reaction), they behave like acids and bases (we call these conjugates)

• Conjugate video

• Conjugate Acid - Particle that forms after the base accepts a proton (H+) from the acid

• Conjugate Base – particle that remains after a proton (H+) has been released by the acid

Ex. HNO3 + NaOH H2O + NaNO3

(H-OH)Acid

Conjugate BaseBaseConjugate acid

Disappearing ink

Ex. KOH + HBr KBr + H2O

Base Conjugate AcidAcid

Conjugate Base

Neutralization Reaction

• Occurs when an acid and a base react and there is a complete removal of all of the H+ and OH- ions

• Water will be formed w/ a salt in this double displacement reaction

• The solution will be neutral in pH• Important in: neutralization of soil,

antacids

Salt

• Crystalline compound composed of the negative (non-metal) ion of the acid and the positive (metallic ) ion of the base

• Salt examples: CaSO4 (plaster board), NaCl, KCl, (NH4)2SO4 (fertilizer)

Examples of Neutralization Reactions

• Sodium hydroxide + hydrochloric acid sodium chloride + water

• NaOH + HCl NaCl + H2O (H-OH)

• Potassium hydroxide + sulfuric acid water + potassium sulfate

• KOH + H2SO4 H- OH + K2SO4

2 KOH + H2SO4 2 H-OH + K2SO4

• Aluminum hydroxide + acetic acid

Titration

Titration

• Used for a convenient method to determine the concentration or molarity of an acid or base

• Uses 2 burets (long glass tubes used to measure volume)- Buret + .05 ml

Definition

• Analytical method in which a standard solution is used to determine the concentration of another solution

• Standard solution- one in which the concentration is known

Process

• Using a given amount of acid in a flask, add phenolphthalein and titrate to the end point with the base (making sure to mark down all the volumes)

• The whole reaction is a neutralization reaction

• Use an indicator to see the endpoint in which complete neutralization occurs (wait for phenolphthalein stays light pink for 30 sec)

Endpoint Past endpoint

Titration Process

Calculations

• Reminder: M= moles• liters• So: Base (titrated soln)

– Moles (base) = volume (base) x Molarity (base)

Acid (standard soln) Moles (acid) = volume (acid) x Molarity (acid)

• Look at balanced equation and find the moles of the standard and the moles of the titrated unknown (look at coefficients)

• Most times it is a 1:1 ratio

• 1 NaOH + 1 HCl NaCl + H2O (H-OH)

• So: 1 mole (base) = 1 mole (acid)

• Therefore: MA VA = MBVB

Problem

• A titration of 15.00 ml of HCl, required 38.57 ml of a 0.152 M base NaOH. Calculate the molarity of the HCl (acid).

• MA = ?

• MA VA = MBVB

• MA = M BVB

• VA

• MA = (.152M) (38.57 ml)

• (15.00ml)

• MA = .391 M

Titration Calculation

ID- A, B, CA, CB

• CaCO3 + HCl CaCl2 + H2CO3

• KOH + H3PO4 K3PO4 + H2O

• phosphoric acid + calcium hydroxide calcium phosphate + water

• HBr + Al(OH)3

• Sulfuric acid + potassium hydroxide

Indicators

• Used to find out if things are acidic or basic

• Def: weak organic acids or bases whose colors differ from the colors of their conjugate acids or bases

acidbase

Needs of Indicators

• Solution being tested needs to be colorless

• You need to be able to distinguish the color change

• Need several indicators to cover entire pH range (0-14)

• Liquid solution

Indicator Examples

• Litmus red turns blue = base, blue turns red = acid

• Phenolphthalein hot pink > pH 10• Bromothymol blue blue= base (8),

Green= neutral, yellow = acid (6)• Universal Indicator Rainbow (all pH’s 4-

10)

• (bromothymol blues)

How Chemists use Indicators

Ionization of H2O

• Pure water can self ionize, it also acts as an acid or a base (amphoteric)

• So: H2O(aq) H+(aq) + OH- (aq)

• Experiments have shown that the concentration of [H+] = 1 X 10 –7M and [OH-] = 1 x 10 –7 M in pure water

• [ ] means concentration

Ion Product Constant for water

• Equilibrium expression from the multiplication of the concentrations of the products

• [H+] [OH-] =?

• (1 x 10 –7)(1 x 10 –7) = 1.0 x 10 -14 1. [H+] [OH-] = 1.0 x 10 -14

• If [H+] = 1.5 x 10 -6 M, what is the [OH-] = ?

• [H+] [OH-] = 1.0 x 10 -14

• (1.5 x 10 -6) [OH-] = 1.0 x 10 -14

• [OH-] = 1.0 x 10 -14

• 1.5 x 10 -6

• [OH- ] = 6.7 x 10-9 M

pH Concept (video)

• Acidity scale developed by Soren Sorenson base on the “power of the hydrogen”

• pH – measure of the hydrogen ion concentration of the solution– Equal to the negative logarithm of the

hydrogen ion concentration

2. pH = - log [H+]

Ex. [H+] = 1.5 x 10-8

pH= ?

Graphing Calc. (-) log 1.5 (2nd) EE -8

Regular calc. 1.5 EE -8 log +/- pH= 7.8

To go from pH to [H+]concentration

3. [H+] = antilog (-pH)

Antilog = 10x key

• pH= 3.5• [H+] = ?[H+] = antilog (-pH)[H+] = antilog (-3.5)Graphing = 2nd log -3.5Regular 3.5 +/- 2nd log (to put in sci.not. Use 2nd #5)[H+] = 3.2 x 10 -4 M

pOH (hydroxide power)

4. pH + pOH =14• pH= 8 • pOH = ?8 + ? = 14 pOH= 6

5. pOH = - log [OH-]6. [OH-] = antilog (-pOH)

• [H+] = 3.5 x 10 -7 M, [OH-] = ?

• pH = 8.95 , [H+] = ?

• [OH-] = 5.65 x 10 -2 M, pOH = ?

• pOH= 11.9, [H+] = ??

• Formula 1

• Formula 3• Formula 5

• Formula 4, then 3 or• Formula 6, then 1

Rosengarten acid and base video