acids - chemchem.ws/dl-1008/07a-acids.pdf · ‣ the sour odor of rotten meat is due to carboxylic...

Acids

A unique class of substance… and its complement. Acids & Bases.

Ch07

© Nick DeMello, PhD. 2007-2015

version 1.5

Important Dates

‣ This Wednesday: - Lab Checkout (you must check out of your lab locker or you may be fined) - Lab Practical, last lab quiz (25 points) - Last day to turn in past due labs and homework (start of lab period)

‣ Mon, March 21st: Final Exam 9:15-11:15 a.m. you must take the final exam to pass the course Final Exam is worth 120 points Final Exam is cumulative

‣ Mon, April 4th: Final Grades will be submitted to the college. (They won’t be available until they are posted; they will be posted as soon as they are available.)

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Acids

‣ Acids & Bases ‣ Sources & Properties

‣ Liebig Model

‣ Arrhenius Model ‣ Provides H+ & OH1-

‣ Naming

‣ Brønsted-Lowry Model ‣ Accepts/Donates H+

‣ Solvent Effects

‣ Conjugate Base Pairs ‣ Identifying Pairs

‣ Acid Strength ‣ Dissociation/Association

‣ Acids are Electrolytes

‣ Strong & Weak Acids

‣ Base Strength

‣ Equilibrium‣ Reversible Reactions

‣ Reaction Rates

‣ Achieving Equilibrium

‣ Le Chatelier’s Principle ‣ Disturbing Equilibrium

‣ Re-establishing Equilibrium

Ch07

11H+

Acids & Bases

‣ For more than 300 years, substances that behaved like vinegar have been classified as acids.

‣ Substances that have properties like the ash from a wood fire have been called alkalies or bases.

‣ The name "acid" comes from the Latin acidus, which means "sour," and refers to the sharp odor and sour taste of many acids.

‣ Vinegar tastes sour because it is a dilute solution of acetic acid in water.

‣ Lemon juice is sour because it contains citric acid.

‣ Milk turns sour when it spoils because of the formation of lactic acid.

‣ The sour odor of rotten meat is due to carboxylic acids such as butyric acid formed when fat spoils.

Sources and Uses

‣ Acids are all around us. … and are used for diverse purposes.

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Properties

‣ Acids: 1. Taste sour.

2. Turn litmus red.

3. Destroy the properties of bases.

4. Conduct electricity.

5. Produce H2 gas from active metals.

‣ Bases have the properties of: 1. Taste bitter (or chalky).

2. Turn litmus blue.

3. Destroy the properties of acids.

4. Conduct electricity.

5. Feel slippery (“soapy”).

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Litmus is a water soluble mixture of different dyes extracted from lichens. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity.

Litmus was used for the first time about 1300 AD by Spanish alchemist Arnaldus de Villa Nova.

Svante Arrhenius

‣ Justus Liebig proposed that an acid was a hydrogen-containing substance in which the hydrogen could be replaced by a metal. ‣ This definition lasted for over 50 years until a better one came along.

‣ Svante Arrhenius 1883 doctoral thesis presented the idea of electrolytic dissociation — that electrolytes dissociate into ions when placed in water. (At the time, it was thought you needed electric current to form ions.) ‣ Arrhenius got a “D” for his thesis.

‣ It became one of the most widely utilized ideas of the next 1,000 years.

‣ Arrhenius is seen as one of the greatest chemists of that millennia.

‣ He was awarded the nobel price in 1903 for that idea… … the one he got a “D” on.

‣ From the theory of electrolytic dissociate, Arrhenius defined: ‣ Acid is any substance which delivers hydrogen ion (H+) to the solution.

‣ Base is any substance which delivers hydroxide ion (OH¯) to the solution.

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HCl(g) H+(aq) + Cl−(aq)H2O(l)

acid

KOH OH-(aq) + K+(aq)H2O(l)

base

Naming Binary Acids

‣ Binary compounds where one of the two non-metals is hydrogen are not acids. But some become acids when they’re dissolved in water.

‣ Binary compounds only release protons into water.

‣ The binary compounds that become acids are: HF, HCl, HBr, and HI

‣ We indicate something is dissolved in water by putting “(aq)” after it’s formula. Aqueous is Latin for “with water.”

‣ To name a binary acid add “-ic acid” to the anion and prefix the name with “hydro”.

HBr is hydrogen bromide. It’s not an acid.

HBr (aq) is hydrobromic acid.

HCl (aq) is hydrochloric acid, a very powerful acid.

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What’s the name or formula?

Hydrogen BromideHydrobromic AcidHydroiodic Acid

HFHCl (aq)

Answer:

HBrHBr (aq)HI (aq)

Hydrogen FluorideHydrochloric Acid

11H

11H+

+

Naming Oxy-Acids

‣ To name acids of oxy-ions, replace

‣ the “-ate ion” with “-ic acid”

‣ the “-ite ion” with “-ous acid”

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P PO4 3- Phosphate ion H3PO4 Phosphoric acid

PO3 3- Phosphite ion H3PO3 Phosphorous acid

S SO4 2- Sulfate ion H2SO4 Sulfuric acid

SO3 2- Sulfite ion H2SO3 Sulfurous acid

C CO3 2- Carbonate Ion H2CO3 Carbonic acid

CO2 2- Carbonite Ion H2CO2 Carbonous acid

N NO3 1- Nitrate Ion HNO3 Nitric acid

NO2 1- Nitrite Ion HNO2 Nitrous acid

Cl,Br, I ClO41- Perchlorate Ion HClO4 Perchloric acid

ClO31- Chlorate Ion HClO3 Chloric acid

ClO21- Chlorite Ion HClO2 Chlorous acid

ClO1- Hypochlorite Ion HClO Hypochlorous acid

‣ Polyatomic ions with enough hydrogens on them to neutralize their charge become acids.

‣ Oxy acids do not need to be in water to be acids, they are acids with or without (aq).

Arrhenius Bases

‣ Arrhenius bases ‣ produce hydroxide ions (OH−) in water

‣ taste bitter or chalky

‣ are also electrolytes because they produce hydroxide ions (OH1−) in water

‣ feel soapy and slippery

‣ turn litmus indicator paper blue and phenolphthalein indicator pink

‣ Typical Arrhenius bases are named as hydroxides. ‣ NaOH sodium hydroxide

‣ KOH potassium hydroxide

‣ Ba(OH)2 barium hydroxide

‣ Al(OH)3 aluminum hydroxide

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Naming Acids & Bases

What is the name of each of the following?

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A. bromic acid

B. bromous acid

C. hydrobromic acid

A. carbonic acid

B. hydrocarbonic acid

C. carbonous acid

A. bromic acid

B. hydrobromous acid

C. bromous acid

HBr (aq)

H2CO3

HBrO2

Match the formulas with the names.

1. ___ HNO2 A. iodic acid

2. ___ Ca(OH)2 B. sulfuric acid

3. ___ H2SO4 C. sodium hydroxide

4. ___ HIO3 D. nitrous acid

5. ___ NaOH E. calcium hydroxide

ABED

C

Acids


‣ Liebig Model


‣ Naming


‣ Solvent Effects





‣ Base Strength


‣ Reaction Rates




11H+

Ch07

Problems with Arrhenius Model

‣ The Arrhenius model of acids has some problems…

‣ It says solvents play no role in acidity. ‣ HCl is an acid only in water, in benzene it’s not.

‣ It says salts should not produce only neutral solutions. ‣ NaCl in water is acidic.

‣ It caused Arrhenius to suggest the base of ammonia in water is NH4OH. ‣ The actual base is NH3.

‣ NH3 is just as basic in aniline, where no hydroxide is possible.

‣ H+ (a bare proton) doesn’t last long in water. ‣ The lone pairs on water grab it.

‣ Even in the strongest aqueous acid solutionsthe concentration of H+ is something like 10-130 M

‣ The Arrhenius theory of acids and bases was replaced by the theory proposed independently by Johannes Brønsted and Thomas Lowry in 1923.

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Brønsted-Lowry Model

‣ The Brønsted–Lowry theory is an acid–base reaction theory which was proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923.

‣ When an acid and a base react with each other, the acid forms its conjugate base, and the base forms its conjugate acid by exchange of a proton.

‣ According to the Brønsted–Lowry theory: ‣ an acid is a substance that donates H1+

‣ a base is a substance that accepts H1+

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Johannes Brønsted Thomas Lowry

Brønsted-Lowry Model

‣ According to the Brønsted–Lowry theory: ‣ an acid is a substance that donates H1+

‣ a base is a substance that accepts H1+

‣ In the reaction of ammonia and water,

‣ NH3 acts as the base that accepts H+

‣ H2O acts as the acid that donates H+

‣ One either side of the arrow, there is one acid and one base.

‣ The one that’s holding the traded H+ is the acid.

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Identify the Acid

‣ In each of the following equations, identify the Brønsted–Lowry acid and base in the reactants:

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HNO3 (aq) + H2O(l) H3O+(aq) + NO3−(aq)

NH3 (aq) + H3O+(l) H2O (aq) + NH41+(aq)

ACID BASE

ACIDBASE

A B

Summary of Acid-Base Properties

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Acids


‣ Liebig Model


‣ Naming


‣ Solvent Effects





‣ Base Strength


‣ Reaction Rates




11H+

Ch07

Conjugate Acid–Base Pairs

‣ In any acid–base reaction, there are two conjugate acid–base pairs, and ‣ each pair is related by the loss and gain of H+1

‣ each pair is tossing a ball back and forth, the ball is H1+

‣ one pair occurs in the forward direction

‣ one pair occurs in the reverse direction

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HA + B A1- + BH1+

acid and conjugate base pair 1

acid and conjugate base pair 2


‣ Conjugate base pair is the same substance, with and without the proton (hydrogen ion) it is either donating or accepting.

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HA + B ⇄ A1- + BH1+

HA and A1- are one acid base conjugate pair.

HA is the acid. A1- is the base.

B and BH1+ are the other acid base conjugate pair.

B is the base. BH1+ is the acid.


In the acid–base reaction of HF and water…

‣ the first conjugate acid–base pair is HF, which donates H+ to

form its conjugate base, F−

‣ the other conjugate acid–base pair is H2O, which accepts H+ to form its conjugate acid, H3O+

‣ each pair is related by a loss and gain of H+

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In acid-base reaction of ammonia (NH3) and water…

‣ one conjugate acid–base pair is NH3/NH4+

‣ the other conjugate acid–base pair is H2O/H3O+

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Write the conjugate base for…

HBr ➞HNO3 ➞ H3PO4 ➞NH41+ ➞

H2CO3 ➞H3O1+ ➞

H1+ + Br1-H1+ + NO31-H1+ + H2PO41-H1+ + NH3H1+ + HCO31-H1+ + H2O (water)

ACID BASE

Write the conjugate acid for…

Cl1-BrO31- HPO42-

OH1-NH3H2O

+ H1+ ➞ HCl+ H1+ ➞ HBrO3+ H1+ ➞ H2PO41-+ H1+ ➞ H2O (water)+ H1+ ➞ NH41++ H1+ ➞ H3O1+ (hydronium ion)

ACIDBASE

Acids


‣ Liebig Model


‣ Naming


‣ Solvent Effects





‣ Base Strength


‣ Reaction Rates




11H+

Ch07

Acid Strength

‣ Acids are electrolytes.

‣ Electrolyte strength describes the dissociation process of electrolytes. ‣ The stronger they are, the more they break apart.

‣ The stronger they are, the more ions they put into solution.

‣ Acid and base strength is the same process.

‣ Strong acids, put more “H+” into solution.

‣ Stronger bases, put more “OH1-“ (or other proton accepters) into solution.28

Dissocia'onofsodiumchlorideinwater

NaCl(aq) ⇄ Na+(aq) + Cl- (aq)

H2O

Acid Strength







Strongacidsdissociatecompletelyintoions.

HI(s) ➞ H+(aq) + I- (aq)

H2O

Theyproducehighconcentra'onsofH+

Acid Strength







Weakacidsdissolveinwater,butremainmostlyanassociatedpairofions.

HF(aq) ⇄ H+(aq) + F- (aq)

H2O

Theyproducelowconcentra'onsofH+







HB(aq) ⇄ H+(aq) + B- (aq)

H2O

There are six common strong acids.

Acid Strength

• The stronger an acid is at donating H, the weaker the conjugate base is at accepting H.

• Higher oxidation number = stronger oxyacid

• More oxygens in oxyacid = stronger acid – H2SO4 > H2SO3

– HNO3 > HNO2

• Cations are stronger acids than neutral molecules.

• Neutral molecules are stronger acids than anions. – H3O

+ > H2O > OH

−;

– NH4

+ > NH3 > NH2

−

– Trend in base strength opposite

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Acid Strength

Acids


‣ Liebig Model


‣ Naming


‣ Solvent Effects





‣ Base Strength


‣ Reaction Rates




11H+

Ch07

Acid Base Equilibrium

‣ Acid Base reactions are reversible.

‣ In reversible reactions, two reactions are taking place.

‣ The reaction is occurring in both the forward and reverse direction.

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HF(aq) + H2O(l) ⇄ F−(aq) + H3O+(aq)

HF(aq) + H2O(l) ➞ F−(aq) + H3O+(aq)

F−(aq) + H3O+(aq) ➞ HF(aq) + H2O(l)

Forward Reaction

Reverse Reaction

Forward Reaction

Reverse Reaction



‣ Even though there are two reactions going on, by convention we always refer to:

‣ The substances on the left as reactants.

‣ The substances on the right as products.

‣ The rate of the forward reaction depends on how much reactant.

‣ The rate of the reverse reaction depends on how much product.

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Reactants Products

Forward Reaction

Reverse Reaction



‣ As an analogy thinking of population across a border.

‣ When Country A citizens feel overcrowded, some will emigrate to Country B.

‣ When you first dissolve HF in solution, the forward reaction goes faster than the reverse.

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Forward Reaction

Reverse Reaction



‣ The rate of reaction changes with concentration.

‣ As we have less reactant the forward reactionslows.

‣ As we have more product, the reverse reactionspeeds up.

‣ Eventually the two rates are equal.

‣ The concentration of reactants and products becomesconstant.

‣ Even though both reactions are continuing to occur.

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Forward Reaction

Reverse Reaction



‣ As an analogy thinking of population change in countries.

‣ However, after a time, emigration will occur in both directions at the same rate, leading to populations in Country A and Country B that are constant, but not necessarily equal.

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Forward Reaction

Reverse Reaction

That dynamic is Equilibrium

Fill in the Blanks

‣ Complete each of the following with ‣ equal or not equal

‣ faster or slower

‣ change or do not change:

A. Before equilibrium is reached, the concentrations of the reactants and products _____________. (change or do not change?)

B. Initially, reactants have a rate of reaction ______ than the rate of reaction of the products. (faster or slower?)

C. At equilibrium, the rate of the forward reaction is ______ to the rate of the reverse reaction. (equal or not equal?)

D. At equilibrium, the concentrations of the reactants and products ____________. (change or do not change?)

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change

faster

equal

do not change

Acids


‣ Liebig Model


‣ Naming


‣ Solvent Effects





‣ Base Strength


‣ Reaction Rates




11H+

Ch07

Le Châtelier’s Principle

When we alter the concentration of a reactant or product of a system at equilibrium,

‣ the rates of the forward and reverse reactions will no longer be equal

‣ a stress is placed on the equilibrium

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Le Châtelier’s principle states that when equilibrium is disturbed, the rates of the forward

and reverse reactions change to relieve that stress and reestablish equilibrium.


‣ Le Châtelier’s principle predicts how disturbances will effect reaction rates.

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Forward Reaction

Reverse Reaction

That dynamic is Equilibrium

When the populations of Country A and Country B are in equilibrium, the emigration rates between the

two countries are equal so the populations stay constant.



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Forward Reaction

Reverse Reaction

When an influx of population enters Country B from somewhere outside Country A, it disturbs the

equilibrium established between Country A and Country B.



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Forward Reaction

Reverse Reaction

The result will be people moving from Country B into Country A faster than people moving from Country A into Country B.

This will continue until a new equilibrium between the populations is established; the new populations will have different numbers of people than the old ones.



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Forward Reaction

Reverse Reaction



46


Forward Reaction

Reverse Reaction

Reactants Products Products Reactants

Adding F- will… Adding HF will…

Removing F- will… Removing H2O will…

Shift Equilibrium to



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Forward Reaction

Reverse Reaction

Decrease H3O+ Increase H3O+ Increase H3O+ Decrease H3O+

Adding F- will… Adding HF will…

Removing F- will… Removing H2O will…

Effect H3O+ concentration

Acids


‣ Liebig Model


‣ Naming


‣ Solvent Effects





‣ Base Strength


‣ Reaction Rates




11H+

Ch07

Questions?

49

acids - chemchem.ws/dl-1008/07a-acids.pdf · ‣ the sour odor of rotten meat is due to carboxylic...

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