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 concentration2. 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