Chapter 19 Acids and Bases

Questions for Today 1. What are the physical and chemical property of Acids and Bases? 2. How do you classify solutions as acidic, basic, or neutral? 3. Compare and Contrast Arrhenius and Bronsted-Lowry Models of acids and bases. 4. What is a conjugate acid or base and how do you identify it?

Class question  Where can acids be found? Sodas Sodas Stomach Stomach Vinegar Vinegar Citrus fruits Citrus fruits  Where can bases be found? Soap Soap Drano Drano Antacid tablets Antacid tablets Windex Windex detergent detergent

Properties of Acids and Bases  Acids and bases are some of the most important industrial compounds on Earth. We use 30 – 40 billion kg of sulfuric acid each year to make many common products. We use 30 – 40 billion kg of sulfuric acid each year to make many common products.  Acids and Bases can be identified using their chemical and physical property? What are examples of chemical or physical properties? What are examples of chemical or physical properties?

Properties of Acids and Bases  Acids: Taste sour Taste sour Feel like water Feel like water Reacts with Metals Reacts with Metals EffervesenceEffervesence Corrosive Corrosive Turns litmus paper red Turns litmus paper red  Bases Taste Bitter Taste Bitter Feels Slippery Feels Slippery Does not react with Metals Does not react with Metals Reacts with Organic Tissue Reacts with Organic Tissue Caustic BurnsCaustic Burns Turns litmus paper blue Turns litmus paper blue

Strength of Acids & Bases  Strong Acid/Base 100% ionized in water, comes apart completely in water 100% ionized in water, comes apart completely in water Strong electrolyte, conducts electricity Strong electrolyte, conducts electricity Strong Acids: HCl, HNO 3, H 2 SO 4 Strong Acids: HCl, HNO 3, H 2 SO 4 Strong Bases: NaOH, KOH Strong Bases: NaOH, KOH

Strength of Acids & Bases Weak Acid/Base Does not ionize completely, does not come apart completely in water Weak electrolyte, does not conduct electricity well. Weak Acids: HF, CH 3 COOH Weak Base: NH 3

Warning Never use taste in a lab setting to identify acids or bases unless told to by your science teacher.

Acid/Base Indicators  An acid-base indicator is a weak acid or a weak base.  An Indicator changes color over a range of hydrogen ion concentrations. This range is expressed as a pH range.  Some common indicators are: litmus paper, cabbage juice, phenolphthalein bromthymol blue etc.

Identifying and Classifying Acids and Bases  Litmus Paper A chemically treated paper used to identify acids/bases by color comparision. A chemically treated paper used to identify acids/bases by color comparision. Litmus Paper turns redder in the presence of an Acid while, in a base, the paper becomes blue. Litmus Paper turns redder in the presence of an Acid while, in a base, the paper becomes blue.  Electrolytic An electrolyte is any solution that contains ions and can conduct electricity. An electrolyte is any solution that contains ions and can conduct electricity. Both acids and bases can conduct electricity Both acids and bases can conduct electricity Pure Water is a nonconductor of electricity.Pure Water is a nonconductor of electricity.

Identifying and Classifying Acids and Bases  Why are some aqueous solutions acids, bases, or neutral?  The amount of Hydrogen ions (H + ) or Hydroxide ions (OH - ) determines the acidity or basidity of a solution. An Acidic solution contains more H + ions than OH - ions An Acidic solution contains more H + ions than OH - ions A Basic Solution contains more OH - ions than H + ions. A Basic Solution contains more OH - ions than H + ions. Neutral Solutions contain equal amounts of H + ions and OH - ions. Neutral Solutions contain equal amounts of H + ions and OH - ions.

Who “Discovered” Acids?  First chemist to define acids and bases was Swedish chemist, Svante Arrhenius.  The Arrhenius Model states that an acid is a substance that contains hydrogen and ionizes to produce Hydrogen ions (H + ) in aqueous solution while a Base is a substance that contains a Hydroxide group and dissociates to produce a hydroxide ion (OH - ) in aqueous solution.

Example of Arrhenius Model  HCl  H + + Cl - Hydrochloric Acid will dissociate into Hydrogen ions and Chlorine ions when dissolved in Water. Hydrochloric Acid will dissociate into Hydrogen ions and Chlorine ions when dissolved in Water.  NaOH  Na + + OH - When the ionic compound NaOH dissolves in water, it dissociates to produce Hydroxide ions, which makes the solution Basic. When the ionic compound NaOH dissolves in water, it dissociates to produce Hydroxide ions, which makes the solution Basic.

Flaw with Arrhenius model NNNNot all bases contain hydroxide EEEEx: ammonia (NH3) is basic TTTTherefore a new type of acid/base must be determined

Bronsted-Lowry Model  Bronsted-Lowry Acid Defn: proton/H + donor Defn: proton/H + donor can give H + to another speciescan give H + to another species  Bronsted-Lowry Base Defn: proton/H + acceptor Defn: proton/H + acceptor can take H + from another speciescan take H + from another species

Bronsted-Lowry Model RRRREMEMBER!!!! REMEMBER!!!! Acids Donate, Bases Accept protons Ashley donates Blood Always

 Examples HCl + H 2 O  Cl - + H 3 O + What is happening here? Acid (donates proton) Base (accepts proton) Which is the acid? base?

Bronsted-Lowry Model  Examples NH 3 + H 2 O  NH OH - What is happening here? Acid (donates proton) Base (accepts proton) Which is the acid? base?

Amphoteric  Defn – substance that can act as both acids and bases HNO 3 + H 2 O  H 3 O + + NO 3 - NH 3 + H 2 O  NH OH - base acid Water is amphoteric b/c it is acts as a base in one reaction and acts as an acid in the second Is H 2 O a base or acid? Is H 2 O a base or acid?

Neutralization Reactions Strong acid + Strong base  Salt + Water Ex. HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O

Acids & Bases pHpH

The pH Scale  The pH scale indicates the hydronium ion concentration, [H 3 O + ]  In other words how many H 3 O + ions are in a solution. If there are a lot we assume it is an acid, if there are very few it is a base.

The pH Scale 0 7 INCREASING ACIDITY NEUTRAL INCREASING BASICITY 14

The pH Scale pH of Common Substances

Learning Check AB1 Describe the solution in each of the following as: 1) acid 2) base or 3)neutral. A. ___soda B. ___soap B. ___soap C. ___coffee D. ___ wine E. ___ water F. ___ grapefruit F. ___ grapefruit

Solution AB1 Describe each solution as: 1) acid 2) base or 3) neutral. A. _1_ soda B. _2_ soap B. _2_ soap C. _1_ coffee D. _1_ wine E. _3_ water F. _1_ grapefruit F. _1_ grapefruit

Learning Check AB2 Identify each as characteristic of an A) acid or B) base ____ 1. Sour taste ____ 2. Produces OH - in aqueous solutions ____ 3. Chalky taste ____ 3. Chalky taste ____ 4. Is an electrolyte ____ 5. Produces H + in aqueous solutions

Solution AB2 Identify each as a characteristic of an A) acid or B) base _A_ 1. Sour taste _B_ 2. Produces OH - in aqueous solutions _B_ 3. Chalky taste A, B 4. Is an electrolyte _A_ 5. Produces H + in aqueous solutions