LecturePLUS Timberlake

LecturePLUS Timberlake
Do Now #33… Which units are used for the following: q= m= Cp= T= LecturePLUS Timberlake

Objective…. I will be able to determine if a substance (liquid) is either a base or an acid based upon its pH. LecturePLUS Timberlake

Agenda… Learn something today…. LecturePLUS Timberlake

Chapter 9 Acids and Bases
Ionization of Water The pH Scale LecturePLUS Timberlake

Ionization of Water Occasionally, in water, a H+ is transferred between H2O molecules H:O: :O:H H:O:H :O:H- H H H water molecules hydronium hydroxide ion (+) ion (-) LecturePLUS Timberlake

Pure Water is Neutral Pure water contains small, but equal amounts of ions: H3O+ and OH- H2O + H2O H3O OH- hydronium hydroxide ion ion 1 x 10-7 M 1 x 10-7 M H3O+ OH- LecturePLUS Timberlake

Ion Product of Water Kw [ ] = Molar concentration Kw = [ H3O+ ] [ OH- ] = [ 1 x ][ 1 x 10-7 ] = x 10-14 LecturePLUS Timberlake

Acids Increase H+ HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq) More [H3O+] than water > 1 x 10-7M As H3O+ increases, OH- decreases [H3O+] > [OH-] H3O+ OH- LecturePLUS Timberlake

Bases Increase the hydroxide ions (OH-) H2O NaOH (s) Na+(aq) OH- (aq) More [OH-] than water, [OH-] > 1 x 10-7M When OH- increases, H3O+ decreases [OH] > [H3O+] OH- H3O+ LecturePLUS Timberlake

Using Kw The [OH- ] of a solution is 1.0 x M. What is the [H3O+]? Kw = [H3O+ ] [OH- ] = x 10-14 [H3O+] = 1.0 x 10-14 [OH-] [H3O+] = x = 1.0 x M 1.0 x 10- 3 LecturePLUS Timberlake

Learning Check pH1 The [H3O+] of lemon juice is 1.0 x 10-3 M. What is the [OH-] of the solution? 1) 1.0 x 103 M 2) 1.0 x M 3) 1.0 x 1011 M LecturePLUS Timberlake

Do Now #34… What does the water equilibrium Kw (H20Keq) actually mean? What does the number represent? LecturePLUS Timberlake

Objective… I will be able to correctly calculate the pH values of 3 out of 4 reactions correctly and tell if the final pH of the solution is a Acid or Base. LecturePLUS Timberlake

Solution pH1 The [H3O+] of lemon juice is 1.0 x M. What is the [OH-]? [OH- ] = x = 1.0 x M 1.0 x LecturePLUS Timberlake

Learning Check pH2 The [OH-] of a solution is 5 x M. What is the [H3O+ ] of the solution? 1) 2 x M 2) 1 x 1010 M 3) 2 x M LecturePLUS Timberlake

Solution pH2 The [OH-] of a water solution is 5 x 10-5 M. What is the [H3O+] in the solution? [ H3O+] = 1.0 x 5 x 10- 5 LecturePLUS Timberlake

Learning Check pH3 A.The [OH-] when [H3O+ ] of 1 x M 1) 1 x 10-6 M 2) 1 x 10-8 M 3) 1 x M B.The [H3O+] when [OH- ] of 5 x M 1) 1 x M 2) 2 x M 3) 2 x 10-7 M LecturePLUS Timberlake

Solution pH3 Kw = [H3O+ ][OH-] = 1.0 x 10 14 A. (3) [OH- ] = x = 1.0 x 1.0 x 10- 4 B. (2) [H3O+] = x = 2 x 5 x 10- 9 LecturePLUS Timberlake

pH Indicates the acidity [H3O+] of the solution pH = - log [H3O+] From the French pouvoir hydrogene (“hydrogen power” or power of hydrogen) LecturePLUS Timberlake

pH In the expression for [H3O+] 1 x 10-exponent the exponent = pH [H3O+] = 1 x 10-pH M LecturePLUS Timberlake

Do Now #35… A substance with a pH of 2.0 is considered to be a ________. Write the pH as a denomination of a power of 10. LecturePLUS Timberlake

Objective… I will be able to determine the difference between Arrhenius Acids and Bronstead- Lowry acids and bases.

pH Range Neutral [H+]>[OH-] [H+] = [OH-] [OH-]>[H+] Acidic Basic LecturePLUS Timberlake

Some [H3O+] and pH [H3O+] pH 1 x 10-5 M 1 x 10-9 M 1 x M LecturePLUS Timberlake

pH of Some Common Acids gastric juice 1.0 lemon juice 2.3 vinegar orange juice 3.5 coffee milk LecturePLUS Timberlake

pH of Some Common Bases blood tears seawater milk of magnesia 10.6 household ammonia 11.0 LecturePLUS Timberlake

Learning Check pH4 A. The [H3O+] of tomato juice is 1 x 10-4 M. What is the pH of the solution? 1) ) 4 3) 8 B. The [OH-] of an ammonia solution is 1 x 10-3 M. What is the pH of the solution? 1) ) 11 3) -11 LecturePLUS Timberlake

Solution pH4 A. pH = - log [ 1 x 10-4] = -(- 4) = 4 B. [H3O+] = 1 x 10-11 pH = - log [ 1 x ] = -(- 11) = 11 LecturePLUS Timberlake

Learning Check pH5 The pH of a soap is 10. What is the [H3O+] of the soap solution? 1) 1 x M 2) 1 x 1010 M 3) 1 x M LecturePLUS Timberlake

Solution pH5 The pH of a soap is 10. What is the [H3O+] of the soap solution? [H3O+] = 1 x 10-pH M = 1 x M LecturePLUS Timberlake

pH on the Calculator [H3O+] is 4.5 x 10-6 M pH = x EXP(or EE) 6+/- LOG +/- = 5.35 LecturePLUS Timberlake

Learning Check pH6 A soap solution has a [H3O+] = 2 x 10-8 M. What is the pH of the solution? 1) 8 2) 7.7 3) 6 LecturePLUS Timberlake

Solution pH6 A soap solution has a [H3O+] = 2.0 x 10-8 M. What is the pH of the solution? B) EE /- LOG +/- = 7.7 LecturePLUS Timberlake

Learning Check pH7 Identify each solution as 1. acidic basic 3. neutral A. _____ HCl with a pH = 1.5 B. _____ Pancreatic fluid [H+] = 1 x 10-8 M C. _____ Sprite soft drink pH = 3.0 D. _____ pH = 7.0 E. _____ [OH- ] = 3 x M F. _____ [H+ ] = 5 x 10-12 LecturePLUS Timberlake

Solution pH7 Identify each solution as 1. acidic basic 3. neutral A. _1__ HCl with a pH = 1.5 B. _2__ Pancreatic fluid [H+] = 1 x 10-8 M C. _1__ Sprite soft drink pH = 3.0 D. _3__ pH = 7.0 E. _1__ [OH-] = 3 x M F. _2__ [H+] = 5 x 10-12 LecturePLUS Timberlake

Acid Rain Unpolluted rain has a pH of 5.6 Rain with a pH below 5.6 is “acid rain“ CO2 in the air forms carbonic acid CO2 + H2O H2CO3 Adds to H+ of rain H2CO H+ (aq) + HCO3-(aq) Formation of acid rain: 1. Emission of sulfur and nitrogen oxides from the burning of fuels expecially coal with high S content, power stations, oil refineries, vehicles as well as bacterial decomposition, and lighting hitting N2 SO million tons in 1980 NO and NO2 22 million tons in 1980 Mt. St Helens (1980) 400,000 tons SO2 2. Reactions in the atmosphere form SO3 2SO2 + O2  2 SO3 3. Reactions with atmosphere water form acids SO3 + H2O  H2SO4 sulfuric acid NO + H2O  HNO2 nitrous acid HNO2 + H2O  HNO3 nitric acid 4. Effects of Acid Rain Decline in fish populations in rivers and lasts due to toxic effect of Al leached from soil by acid rain Extensive fish kills in spring from runoff due to accumulation of large amounts of acid on the snow Dissolves minerals Mg, Ca, and K from the soil and waxy coatings that protect leaves from bacteria Corrodes metals, textiles, paper and leather LecturePLUS Timberlake

Sources of Acid Rain Power stations Oil refineries Coal with high S content Car and truck emissions Bacterial decomposition, and lighting hitting N2 LecturePLUS Timberlake

SO million tons in 1980 NO and NO million tons in 1980 Mt. St Helens (1980) 400,000 tons SO2 Reactions with oxygen in air form SO3 2SO2 + O2 2 SO3 Reactions with water in air form acids SO3 + H2O H2SO4 sulfuric acid NO + H2O HNO2 nitrous acid HNO2 + H2O HNO3 nitric acid LecturePLUS Timberlake

Effects of Acid Rain Leaches Al from soil, which kills fish Fish kills in spring from runoff due to accumulation of large amounts of acid in snow Dissolves waxy coatings that protect leaves from bacteria Corrodes metals, textiles, paper and leather LecturePLUS Timberlake

Modern Theories of Acids & Bases
The Arrhenius and Bronsted-Lowry Theories

Acids & Bases Acids and bases are special kinds of electrolytes. Like all electrolytes they break up into charged particles. What sets them apart from each other, and other electrolytes is the way that they break up.

Arrhenius Acids Svente Arrhenius (who first proposed the theory of ionization) identified acids as substances that ionize in water to produce hydronium ion. For example: HCl + H2O  H3O+ + Cl- Any substance that ionizes in water to produce hydronium ion can be classified as an acid.

H3O+ (aka H+) The hydronium ion is also known as a hydrogen ion. This allows us to shorten the ionization reactions for acids. The following equations represent the same chemical change: HCl + H2O  H3O+ + Cl- and HCl  H Cl- However, it should be understood that H+ is an abbreviation for the hydronium ion. H+ ions DO NOT exist in water solution but are snatched up by water molecules to form hydronium ions.

Arrhenius Base Svente Arrhenius also identified bases as substances that ionize in water to produce hydroxide ion. For example: NaOH  Na+ + OH- Any substance that ionizes in water to produce hydroxide ion can be classified as a base.

Properties of Acids Why? All acids have the following properties:
Neutralize bases to form a salt and water Have a sour taste (example: citric acid, vinegar) React with metals to produce a salt plus hydrogen gas. Have pH’s less than 7 / Affect indicators Why? Because all acids have H3O+ ions present!

Properties of Bases Why? All bases have the following properties:
Neutralize acids to form a salt and water Have a bitter taste (example: unsweetened chocolate, heroin) Are slippery. React with fats/oils to form soap (saponification) Have pH’s greater than 7 / Affect indicators Why? Because all bases have OH- ions present!

Salts Ionic substances that break up in solution to produce ions other than hydronium and hydroxide ions. NaCl (s)  Na+(aq) + Cl- (aq) KNO3(s)  K+ (aq) NO3- (aq) Li2SO4 (s)  2 Li+ (aq) + SO42-(aq) Salts are made up of positive (metal) and negative (non-metallic or polyatomic) ions. The more familiar you become with Table E, the easier it will be for you to identify salts.

Practice Identify each of the following as acids/bases/salts: HC2H3O2
K2SO4 KOH LiOH HNO3 Acid HC2H3O2 H+ + C2H3O2- Salt K2SO4  2K+ + SO42- Base KOH  K OH- Base LiOH  Li OH- Acid HNO3  H NO3-

Strong/Weak Acids Acids can be either strong electrolytes or weak electrolytes. Strong acids (such as HCl) completely break up into their ions: HCl (aq)  H+(aq) Cl-(aq) Weak acids (such as HC2H3O2) only partially break up into their ions: HC2H3O2  H+ (aq) + C2H3O2-(aq) Weak acids don’t completely break up because they go to equilibrium!

Strong/Weak Bases Bases can be either strong electrolytes or weak electrolytes. Strong bases (such as NaOH) completely break up into their ions: NaOH (aq)  Na+(aq) OH-(aq) Weak bases (such as NH3) only partially break up into their ions: NH3 (aq) + H2 O  NH4+ (aq) + OH-(aq) Weak bases don’t completely break up because they go to equilibrium!

Bronsted-Lowry Acids & Bases
Another theory of acids & bases

Not everyone was happy with Arrhenius’s definition
A major problem with the Arrhenius definition of acids and bases is that it limits acids and bases to water (aqueous) solutions. Since an acid requires water to ionize and form hydronium ions, there can be no Arrhenius acids unless water is involved as the solvent.

Relationship between the two models
Bronsted-Lowry Acids/Bases can exist when no water is present Arrhenius Acids/Bases only exist in water solutions. All Arrhenius acids and bases can also be classified as Bronsted-Lowry acids and bases.

Bronsted-Lowry Definitions
Bronsted and Lowry felt that this was too limiting, since there are many non-aqueous systems (no water is present). They came up with the following definitions for acids and bases. An acid is a proton (H+ ion) donor A base is a proton acceptor

An example In the reaction below there are no Arrhenius acids or bases present (because no hydronium ions or hydroxide ions are formed). However, the HCl is acting as a Bronsted-Lowry acid because it is giving a H+ ion to the NH3 (which is acting as a H+ ion acceptor - a base)

Acid & Bases are Roles In the Bronsted-Lowry definition, substances are classified as acids or bases depending on how they behave in a given situation. This means that the same substance can act as a acid in one reaction (by donating a proton) while acting as a base in another reaction

HCl as a proton donor Consider the following reaction:
Since the HCl gives up a H+ ion to the water it is acting as a Bronsted-Lowry acid. In the process of donating the proton it also forms a hydronium ion, and that makes it an Arrhenius acid as well.

Water as a base But what does that make the water molecule?
Since the water molecule is accepting the H+ ion, it is acting as a Bronsted-Lowry base. Since there is no hydroxide ion (OH-) formed, the water is not acting as an Arrhenius base in this reaction.

Ammonia as a base Let’s look at another example:
Here the ammonia molecule is accepting a H+ ion and therefore is acting as an Bronsted-Lowry base. However, in the process of reacting with the water it is also forming a hydroxide ion. That makes the ammonia an Arrhenius base as well.

But what about the water?
Since the water is giving up a H+ ion, it is acting as a Bronsted-Lowry acid. Since it does not form hydronium ions, it is NOT acting an Arrhenius acid.

So is water an acid or a base?
In one example, we said that water was acting as a base, and in another example we said that it was acting as an acid. Some of you may be confused by this because you are thinking of acids and bases as being like boys and girls. Boys are boys and girls are girls, and they can’t switch back and forth. However, acids and bases are NOT like this.

Teacher-student model
Teachers give off information (like acids give off protons) Students accept information (like bases accept protons) Sometimes teachers are students, and sometimes students are teachers Teacher and students are roles that individuals play depending on the situation. Acid and base are roles that molecules play in a particular chemical reaction. In different reactions they may play different roles.

Amphiprotic Sometimes a molecule can donate a proton (act as an acid) and sometimes it can accept a proton (act as a base). Molecules that have this ability to act as both an acid and a base are called amphoteric or amphiprotic. Water is the most common example of an amphoteric substance.

Reality check For each of the following reactions identify any Bronsted-Lowry acids and bases. HNO H2O  H3O NO3- HNO NH3  NH NO3- S H2O  HS OH- HS OH-  S H-OH HS HCl  H2S Cl- Are any of the substances above amphoteric? acid base acid base base acid acid base base acid

Acid-base equilibrium
Many acid base reactions go to equilibrium, that is they have both a forward and reverse reactions For instance, acetic acid (HC2H3O2) reacts with water to form hydronium ion and acetate ion.

The reverse reaction However, the acetic acid only partially ionizes because a reverse reaction takes place preventing the forward reaction from reaching completion. In the reverse reaction, the Hydronium ion acts as an acid (a proton donor) while the acetate ion acts as the base.

Every acid has a conjugative base
Conjugate Acid-Bases When a substance donates a proton, the substance that is left is its conjugative base: Notice that the conjugative base is accepting a proton in the reverse reaction. Every acid has a conjugative base

Conjugative Acid-Base Pairs 2
When a substance accepts a proton, the substance that is formed is its conjugative acid: Notice that the conjugative acid is donating a proton in the reverse reaction. Every base has a conjugative acid

Identify the amphoteric substances in this chart.

Salts Salts are generally defined as ionic substances that PRIMARILY produce positive and negative ions other than hydronium or hydroxide when they dissolve in water.

Salts can be classified as being:
Types of Salts Salts can be classified as being: neutral acidic Basic How a salt is classified depends upon whether secondary reactions between the ions making up the salt and water form either hydronium or hydroxide ions.

Determining the type of salt
The type of salt for a particular salt can be determined experimentally by testing the salt solution with universal indicator paper. neutral salts will have a pH of 7 acidic salts will have a pH of less than 7 basic salts will have a pH of greater than 7 Typically, the pH values of salt solutions will be closer to 7 than that of acids or bases.

Predicting the type of salt
All salts can be considered to be formed from their “parent” acid and base by means of the neutralization reaction. Acid Base  Salt + Water The type of salt can be theoretically predicted based on the properties of the “parent” acid and the “parent” base.

Neutral Salts Neutral salts are formed from a reaction between a strong acid and a strong base. (Remember neutralization reactions are double replacement reactions.) For instance, HCl NaOH  NaCl HOH (since HCl is a strong acid and NaOH is a strong base, NaCl is a neutral salt.)

Acidic Salts Acidic salts are formed from a strong acid and a weak base. For instance, HCl NH4OH  NH4Cl HOH (since HCl is a strong acid and NH4OH is a weak base, NH4Cl is an acidic salt.)

Basic Salts Basic salts are formed from a weak acid and a strong base.
For instance, HC2H3O NaOH  NaC2H3O HOH (since HC2H3O2 is a weak acid and NaOH is a strong base, NaC2H3O2 is a basic salt.)

Strong and weak acids In predicting the type of salt it is helpful to remember the three strong acids: HCl – hydrochloric acid HNO3 – nitric acid H2SO4 – sulfuric acid Most other acids are weak. Acetic acid (HC2H3O2) is the most common weak acid discussed in Regents chemistry.

Strong and Weak Bases For bases, the Group I hydroxides are all strong bases. LiOH – lithium hydroxide NaOH – sodium hydroxide KOH – potassium hydroxide Most other hydroxides can be considered as weak bases. Ammonia or Ammonium hydroxide (NH3 or NH4OH) is the most common weak base discussed in Regents chemistry.

Try these Identify the parent acid and base for the following salts, identify them as strong or weak and predict the type of salt formed.

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