ACIDS AND BASES We will begin with properties and… Then look at acids and bases by comparing three different definitions. The definitions start with a vary narrow, specific definition and proceed to a broad definition.

Acids and Bases Acids: Properties and Examples Properties –Sour Taste –React with Metals –Turn Litmus Paper Red

Acids and Bases Reactions of Acids and Bases Acid Reactions –Acids React with Metals –Produces Hydrogen Gas

Acids and Bases Acids: Properties and Examples Examples –Hydrochloric Acid HCl Metal Industry –Sulfuric Acid H 2 SO 4 Fertilizers

Acids and Bases Acids: Properties and Examples Examples –Nitric Acid HNO 3 Fertilizers –Acetic Acid HC 2 H 3 O 2 Vinegar –Phosphoric Acid H 3 PO 4 Soda, pop Phosphoric acid

Acid Rain NO, NO 2, CO 2, SO 2, and SO 3 gases from industrial processes can dissolve in atmospheric water to produce acidic solutions. example: Very acidic rain is known as acid rain. Acid rain can erode statues and affect ecosystems.

Acid Precipitation Chapter 14

Acids and Bases Bases: Properties and Examples Properties –Bitter Taste –Slippery Feel –Turn Litmus Paper Blue

Acids and Bases Bases: Properties and Examples Examples –Sodium Hydroxide (NaOH) –Potassium Hydroxide (KOH) –Ammonia (NH 4 OH) –Sodium Bicarbonate (NaHCO 3 )

Acids and Bases Reactions of Acids and Bases Antacids and Heartburn –Burning in the Lower Throat and Stomach –Reflux of Stomach Acid –Mylanta and Phillips Contain a Base –Neutralizes the Stomach Acid

Neutralization Reactions for Strong Acid & Strong Base H 3 O + + OH -  2H 2 O + salt (ionic compound)

Neutralization Reactions Strong Acid-Strong Base Neutralization In aqueous solutions, neutralization is the reaction of hydronium ions and hydroxide ions to form water molecules. A salt is an ionic compound composed of a cation from a base and an anion from an acid.

Molecular Definitions of Acids and Bases Arrhenius Definition –Acids Produces H + ions in Solution Examples include, HCl, H 2 SO 4,HNO 3 –Bases Produces OH – ions in Solution Examples include NaOH, KOH, Ca(OH) 2

Hydronium Ion –H 3 O + –H + ions in Water Always Associate with Water Molecular Definitions of Acids and Bases

Brønsted–Lowery Definition –Acid Proton (H + ) Donor –Base Proton (H + ) Acceptor

BASE accepts an H + in a chemical reaction. Any Arrhenius base is also a Bronsted-Lowry base. The common base ammonia, NH 3, is a Bronsted-Lowry Base but not an Arrhenius Base. Molecular Definitions of Acids and Bases

Brønsted–Lowery Definition Molecular Definitions of Acids and Bases

A B B A 1. HCl + OH -  Cl - + H 2 O |__________\____________| / \______________________/ 2. H 2 O + H 2 O  H 3 O + + OH - 3. H 2 SO 4 + OH -  HSO H 2 O 4.HCO NH 3  NH CO HCl + HCO 3 -  Cl - + H 2 CO NH HCO 3 -  NH 3 + H 2 CO 3 Can you find any species that are amphoteric? PRACTICE: Bronsted-Lowry Acids and Bases Label the reactant that is the Bronsted-Lowry acid with an A and the base with a B.

Lewis Acid & Base A Lewis acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond. The Lewis definition is the broadest of the three acid definitions. A bare proton (hydrogen ion) is a Lewis acid

Lewis Acids and Bases, continued The formula for a Lewis acid need not include hydrogen. The silver ion can be a Lewis acid Any compound in which the central atom has three valence electrons and forms three covalent bonds will react as a Lewis acid.

Acid & Base Definitions… For our purposes, we will work with the Arrhenius definition: Acids Produces H + ions in Solution Bases Produces OH – ions in Solution

Which of the following are bases according to the Arrhenius concept and which are better described as bases by the Bronsted concept? NaOH Na 2 CO 3 Ca(OH) 2 KCN NaC 2 H 3 O 2

Acids and Bases Strong and Weak Acids and Bases Strong Acids –Completely Ionizes in Solution –Conjugate base is weak. –HCl

Acids and Bases Strong and Weak Acids and Bases Strong Acids –Strong Electrolyte common strong acids are HCl, HBr, HI, HNO 3, H 2 SO 4 and HClO 4

Acids and Bases Strong and Weak Acids and Bases Weak Acids –Does NOT Completely Ionize in Solution common weak acids are all other acids

Acids and Bases Strong and Weak Acids and Bases Weak Acids –Weak Electrolyte –HF

Acids and Bases Strong and Weak Acids and Bases Strong Base –Completely Dissociates in Solution common strong bases are: NaOH and KOH

Acids and Bases Strong and Weak Acids and Bases Weak Base Form OH – by accepting a Proton from Water common weak bases are all other bases. NH 3

Acids and Bases Water: Acid and Base in One Acts as an Acid and a Base Amphoteric

In the self-ionization of water, two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton. Self-Ionization of Water In water at 25°C, [H 3 O + ] = 1.0 ×10 −7 M and [OH − ] = 1.0 × 10 −7 M. The ionization constant of water, K w, is expressed by the following equation. K w = [H 3 O + ][OH − ] At 25°C, K w = [H 3 O + ][OH − ] = (1.0 × 10 −7 )(1.0 × 10 −7 ) = 1.0 × 10 −14

Relationship of [H 3 O + ] to [OH – ]

Acids and Bases Water: Acid and Base in One Neutral Solution –[H 3 O + ] = [OH – ] = 1.0 X 10 –7 M Acidic Solution –[H 3 O + ] > 1.0 X 10 –7 M –[OH – ] < 1.0 X 10 –7 M Basic Solution –[OH – ] > 1.0 X 10 –7 M –[H 3 O + ] < 1.0 X 10 –7 M All Aqueous Solutions –[H 3 O][OH – ] = 1.0 X 10 –14 M = K w

Acids and Bases Acid–Base Titrations Titration –Reactant of Known Concentration –Reacted with Another Reactant of Unknown Concentration –Endpoint

Indicators Indicators are chemicals that undergo the same type of reaction as the main reaction but do it after the completion of the main reaction. An indicator also changes color as it reacts. If you are going to react an acid and a base in a process called a TITRATION, you will need some way to tell when the reaction is complete. Use an indicator.

Indicators Phenolphthalein is an indicator often used in chemistry. Phenolphthalein is colorless in an acid solution and pink in a base solution. Phenolphthalein is also a laxative and was the active ingredient in EX-LAX for a long time. Phenolphthalein was discovered to be cancer causing if taken in too high of a dose.

Indicators Trivia… Phenolphthalein is also one of the few English words with five consonants in a row. phenoLPHTHalein. Can you think of any others?

Acids and Bases The pH Scale: A Way to Express Acidity and Basicity Compact Way to Express Acidity –pH < 7 is Acidic –pH > 7 is Basic –pH = 7 is Neutral

Acids and Bases The pH Scale: A Way to Express Acidity and Basicity Calculating pH pH = –log[H 3 O + ]

Acids and Bases The pH Scale: A Way to Express Acidity and Basicity Calculating pH the lower case “p” stands for “-log” the “H” stands for the [H + ] or molar concentration: pH = –log[H 3 O + ]

pH Calculations Let’s try some pH calculations. If [H + ] = 0.30 log(0.30) = and -log(0.30) = 0.52 so pH = 0.52 This solution is acidic. [H + ] = 4.66 X log(4.66 X ) = log(4.66 X ) = 5.33 pH = 5.33 This solution is also acidic.

pH Calculations [H + ] = 9.3 X log (9.3 X ) = log(9.3 X ) = pH = This solution is basic. There is another term called pOH. It is the -log[OH - ] It is calculated the same basic way as pH. pH and pOH are related.  pH + pOH = 14.

pH Calculations So, if the pH is 11.03, then the pOH would be: pOH = 14 and pOH = If [OH - ] = 4.89 X then log [OH - ] = and pOH = Also, pH would equal: 14 = pH pH = This solution is basic.

EQUATIONS TO LEARN You should know the following equations: pH = -log[H + ] pOH = -log[OH - ] pH + pOH = 14 [H + ][OH - ] = 1 X The following type of problem would make a GREAT quiz problem!

pH = -log[H + ]pOH = -log[OH - ] pH + pOH = 14[H + ][OH - ] = 1 X Complete the following table: This will take us a few minutes

pH = -log[H + ]pOH = -log[OH - ] pH + pOH = 14[H + ][OH - ] = 1 X [H + ] = 4.55 X so pH is pH = 7.34 and pOH = 6.66 [OH - ][H + ] = 1 x so [OH - ] = (1 X )/(4.55 x ) = 2.2 x 10 -7

pH = -log[H + ]pOH = -log[OH - ] pH + pOH = 14[H + ][OH - ] = 1 X Now the table looks like this:

pH = -log[H + ]pOH = -log[OH - ] pH + pOH = 14[H + ][OH - ] = 1 X Now let’s go to the next problem where [OH - ] = 8.02 X So, pOH is pOH = 3.10 and pH is pH = [H + ] = 1.25 X Are these what you get for the answers?

pH = -log[H + ]pOH = -log[OH - ] pH + pOH = 14[H + ][OH - ] = 1 X Now our table looks like this:

pH = -log[H + ]pOH = -log[OH - ] pH + pOH = 14[H + ][OH - ] = 1 X The last problem says that the pH = We can quickly figure out that the pOH will be equal to 8.13 since pH + pOH = 14. So, how do we figure out the [H + ]? When you are given the pH, use this equation to solve for [H + ] [H + ] = 10 -pH

pH = -log[H + ] pOH = -log[OH - ] pH + pOH = 14 [H + ][OH - ] = 1 X [H + ] = 10 -pH So, if pH = 5.87, then [H + ] = Find the button on your calculator that looks like this: 10 X The “x” term will be the negative pH. [H + ] = = 1.35 X 10 -6

pH = -log[H + ] pOH = -log[OH - ] pH + pOH = 14 [H + ][OH - ] = 1 X [H + ] = 10 -pH Now that we know the [H + ], we can figure out the [OH - ] and we will be done. [OH - ] = (1 X )/(1.35 X ) = 7.41 X Now, finally, our completed table looks like this:

pH = -log[H + ] pOH = -log[OH - ] pH + pOH = 14 [H + ][OH - ] = 1 X [H + ] = 10 -pH

Acid–Base Titrations Calculations The titration of mL of an HCl solution of unknown concentration requires mL of a M NaOH solution to reach the endpoint. What is the concentration of the unknown HCl solution? Given: mL HCl mL of M NaOH Find: Concentration of HCl Equations: HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq) Molarity = Moles Liters

Acids and Bases Acid–Base Titrations The titration of mL of an HCl solution of unknown concentration requires mL of a M NaOH solution to reach the endpoint. What is the concentration of the unknown HCl solution? HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq)

Acids and Bases Acid–Base Titrations (Stoichiometry with Molarity) The titration of mL of an HCl solution of unknown concentration requires mL of a M NaOH solution to reach the endpoint. What is the concentration of the unknown HCl solution? HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq) mL NaOH X 1 L X mol NaOH X 1 mol HCL = 1.25 X 10 –5 mol HCl 1000 mL L NaOH 1 mol NaOH Molarity = 1.25 X 10 –5 mol HCl = M HCl L

Acids and Bases Buffers: Solutions that Resist pH Change Resists pH Change Neutralizes Acid or Base that is Added

Acids and Bases Buffers: Solutions that Resist pH Change Buffers Resist pH Change Buffers Contain Significant Amounts of Weak Acid and its Conjugate Base Weak Acid Neutralizes added Base Conjugate Base Neutralizes Added Acid

MORE ON ACID RAIN….

Acids and Bases Acid Rain: An Environmental Problem Related to Fossil Fuel Combustion Fossil Fuels Contribute to Acid Rain

Normal rain has a pH of about 5.8 because of the impact of CO 2 on the rain. CO 2 + H 2 O  H 2 CO 3 In words… Carbon dioxide combines with water to produce carbonic acid. Acid rain has a pH that is less than 5.8.

Acids and Bases Acid Rain: An Environmental Problem Related to Fossil Fuel Combustion Acid Rain Damage

Acids and Bases Acid Rain: An Environmental Problem Related to Fossil Fuel Combustion Acid Rain Legislation pH of Acid Rain

Acid Rain There are two main sources of acid rain. One source is the combustion of large quantities of fossil fuels such as coal and oil. These fossil fuels contain sulfur. During combustion, sulfur reacts like this: S + O 2  SO 2

Acid Rain Sulfur dioxide, if it gets into the atmosphere, can do this: SO 2 + O 3  SO 3 + O 2 or this SO 2 + H 2 O  H 2 SO 3 sulfurous acid SO 3 + H 2 O  H 2 SO 4 sulfuric acid

Acid Rain So, the more fossil fuels we burn, the greater the amount of sulfur dioxide that potentially can be emitted into the atmosphere. This sulfur dioxide will lead to one of the two main forms of acid rain.

Acid Rain The second form of acid rain comes from the combustion of fossil fuels in an internal combustion engine such as a car or truck. n When the gasoline burns in air, there is also a large amount of nitrogen that will burn. n N 2 + O 2 --> NO x n NO x means that there are many possibilities

Acid Rain NO x will react with water and ozone, O 3, just like SO 2 did (although the reactions are more complex) and produce… HNO 3 (nitric acid) Which is the other component of acid rain.

Acids and Bases Chemical Principles Acid Properties Base Properties Molecular Definitions of Acids and Bases Reactions of Acids and Bases Acid–Base Titrations Strong and Weak Acids and Bases Self Ionizing Water pH Scale Buffers Acid Rain

Acids and Bases Chemical Skills Identifying Brønsted–Lowery Acids and Bases Writing Equations for Neutralization Reactions Writing Equations for the Reactions of Acids with Metals and Metal Oxides Acid–Base Titrations Determining [H 3 O + ] in Acid Solutions

Acids and Bases Chemical Skills Determining [OH – ] in Base Solutions Finding the Concentrations of [H 3 O + ] and [OH – ] Calculating pH from [H 3 O + ] Calculating pH from [OH – ] Calculating [H 3 O + ] from pH Calculating [OH – ] from pH