Introduction to Acids, Bases and Salts

Arrhenius Definition of Acids and Bases Acids produce H + in aqueous (water) solutions Acids produce H + in aqueous (water) solutions water water HCl H + (aq) + Cl - (aq) Bases produce OH - in aqueous (water) solutions Bases produce OH - in aqueous (water) solutions water water NaOH Na + (aq) + OH - (aq) NaOH Na + (aq) + OH - (aq)

The Hydronium Ion (H ) Acids produce the H + ion Acids produce the H + ion This is just a “bare proton” and is very reactive. This is just a “bare proton” and is very reactive. It immediately forms a coordinate covalent bond with nearby water molecules to form (H ). It immediately forms a coordinate covalent bond with nearby water molecules to form (H ).

Acids þ Produce H + (as H 3 O + ) ions in water þ Electrolytes (conduct in solution) þ Taste sour þ pH is < 7 þ Corrode metals (see Table J) þ React with bases to form salts and water (Neutralization)

Bases Produce OH - ions in water Produce OH - ions in water Electrolytes (conduct in solution) Electrolytes (conduct in solution) Taste bitter, chalky Taste bitter, chalky pH is >7 pH is >7 Feel soapy, slippery Feel soapy, slippery React with acids to form salts and water (Neutralization) React with acids to form salts and water (Neutralization)

7 Learning Check 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

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

9 Learning Check 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

10 Solution 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

11 Some Common Acids See Table K HCl hydrochloric acid HNO 3 nitric acid H 3 PO 4 phosphor ic acid H 3 PO 4 phosphor ic acid H 2 SO 4 sulfur ic acid HC 2 H 3 O 2 acet ic acid

Naming Acids (Honors) Binary Acids Binary Acids (Contain 2 elements only) (Contain 2 elements only) Ex:HCl, HBr, H 2 S, HF Ex:HCl, HBr, H 2 S, HF Hydro __________ ic Acid Hydro __________ ic Acid

Naming Acids (Honors) Ternary Acids Ternary Acids (Contain hydrogen and a polyatomic ion) (Contain hydrogen and a polyatomic ion) Do NOT start with “Hydro” Do NOT start with “Hydro” Look at name of polyatomic ion Look at name of polyatomic ion If it ends in “ate” the acid ends in “ic” If it ends in “ate” the acid ends in “ic” If it ends in “ite” the acid ends in “ous” If it ends in “ite” the acid ends in “ous”

Name These Acids HBr HBr HNO 3 HNO 3 H 3 PO 4 H 3 PO 4 HNO 2 HNO 2 H 2 C 2 O 4 H 2 C 2 O 4 HClO HClO HBrO HBrO HClO 4 HClO 4 H 2 S H 2 S HIO 3 HIO 3

Name These Acids HBr = hydrobromic acid HNO 3 = nitric acid H 3 PO 4 = phosphoric acid HNO 2 = nitrous acid H 2 C 2 O 4 = oxalic acid HClO = hypochlorous acid HBrO = hypobromous acid HClO 4 = perchloric acid H 2 S = hydrosulfuric acid HIO 3 = iodic acid

Organic Acids Contain carbon Contain carbon Only one of the hydrogens is “acidic” and dissociates in solution Only one of the hydrogens is “acidic” and dissociates in solution Ex:Acetic Acid Ex:Acetic Acid HC 2 H 3 O 2 or CH 3 COOH HC 2 H 3 O 2 or CH 3 COOH

Naming Bases Name them like any other ionic compound. Name them like any other ionic compound. Name usually ends in “hydroxide” Name usually ends in “hydroxide” Ex: LiOH = lithium hydroxide Ex: LiOH = lithium hydroxide

18 Some Common Bases See Table L NaOHsodium hydroxide KOH potassium hydroxide Ba(OH) 2 barium hydroxide Mg(OH) 2 magnesium hydroxide Al(OH) 3 aluminum hydroxide

Important Note There are no “organic bases” (containing carbon). There are no “organic bases” (containing carbon). C 2 H 5 OH for example is not a base. It is an alcohol. The OH on this molecule does not dissociate to form OH - (hydroxide ion)

Salts “Salts” are ionic compounds that are not acids or bases. “Salts” are ionic compounds that are not acids or bases. Metal cation (+) & nonmetal anion (-) Metal cation (+) & nonmetal anion (-) They are electrolytes They are electrolytes Ex: NaCl, MgSO 4, Li 2 S Ex: NaCl, MgSO 4, Li 2 S

21 Learning Check Acid, Base Name Acid, Base Name or Salt CaCl 2 _____________________ KOH_____________________ Ba(OH) 2 ______ _______________ HBr_____________________ H 2 SO 4 ______________________

Answers Acid,Base Name or Salt CaCl 2 saltcalcium chloride KOHbasepotassium hydroxide Ba(OH) 2 basebarium hydroxide HBracidhydrobromic acid H 2 SO 4 acidsulfuric acid

Dissociation Dissociation: when a compound splits apart into ions in solution. Dissociation: when a compound splits apart into ions in solution. How might these dissociate? H 2 SO 4 KOH

Acids React with Metals See Reference Table J See Reference Table J Metals above Hydrogen on the table will react with acids to form a salt and H 2 gas Metals above Hydrogen on the table will react with acids to form a salt and H 2 gas Single Replacement Reaction Single Replacement Reaction 2Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g)

Will an acid react with these metals? If so complete and balance the single replacement reaction. If so complete and balance the single replacement reaction. Mg + HNO 3 Cu + HCl Ca + H 2 SO 4

Answers Mg + 2HNO 3 Mg(NO 3 ) 2 + H 2 Cu + HClNo reaction Cu in below hydrogen on Table J Ca + H 2 SO 4 Ca(SO 4 ) + H 2

Acid, Bases and Metals BBC (good for Indicators) Acid, Bases and Metals BBC (good for Indicators) cience/chemical_material_behaviour/acids _bases_metals/activity.shtml cience/chemical_material_behaviour/acids _bases_metals/activity.shtml cience/chemical_material_behaviour/acids _bases_metals/activity.shtml cience/chemical_material_behaviour/acids _bases_metals/activity.shtml

Pure Water is Neutral Self Ionization of Water: a small quantity of water molecules in a sample will self ionize. This results in a small, but equal amount of H + and OH - H 2 O H + + OH - H 2 O H + + OH - Hydrogen Ion = Hydroxide Ion [H + ] = [OH - ] H+H+ OH -

Self Ionization of Water

Acids Increase the H + concentration Increase the H + concentration As H + increases, OH - decreases As H + increases, OH - decreases [H + ] > [OH - ] H+H+ OH -

Bases Increase the hydroxide ion (OH - ) concentration Increase the hydroxide ion (OH - ) concentration When OH - increases, H + decreases When OH - increases, H + decreases [OH  ] > [H + ] H+H+ OH -

Important Summary Acidic:[H+] > [OH-] Acidic:[H+] > [OH-] Basic:[H+] < [OH-] Basic:[H+] < [OH-] Neutral:[H+] = [OH-] Neutral:[H+] = [OH-]

Determining if it is an Acid or Base How can you tell if something is acidic or basic? How can you tell if something is acidic or basic?

Use an electronic pH meter Use an electronic pH meter

Use an indicator such as litmus Use an indicator such as litmus

Use pH paper containing universal indicator Use pH paper containing universal indicator

Acid/Bases Indicators See Table M Examples: Litmus Litmus pH range for color change (4.5 – 8.3) pH range for color change (4.5 – 8.3) Color change: red to blue Color change: red to blue Phenolphthalein Phenolphthalein pH range for color change (8 - 9) pH range for color change (8 - 9) Color change: colorless to pink Color change: colorless to pink What color would these be if the pH = 10? pH = 3?

pH Scale Neutral [H + ] > [OH - ] [H + ] = [OH - ] [OH - ] > [H + ] Acidic Basic

Pretty Hydrangeas The color of hydrangea flowers depends on the pH of the soil. The color of hydrangea flowers depends on the pH of the soil.

What is pH? Tells us the relative quantity of H + ions (or the acidity) in solution. Tells us the relative quantity of H + ions (or the acidity) in solution. The greater the [H + ] the lower the pH. The greater the [H + ] the lower the pH.

Calculating pH pH = - log [H + ] From the French pouvoir hydrogene From the French pouvoir hydrogene (“hydrogen power” or power of (“hydrogen power” or power of hydrogen) hydrogen)

43 [H + ] pH 1 x M 5 1 x M 9 1 x M 11

Calculating pOH What if you are given the concentration of a base? What if you are given the concentration of a base? Ex: M LiOH Ex: M LiOH You need to find the pOH!!

pOH pOH = -log [OH - ] Ex: M LiOH = 1 x pOH = 6 Ex:.0001M NaOH = 1 x pOH = 4

How can you find pH of a Base? Easy!!! Easy!!! pH + pOH = 14 Ex: M LiOH = 1 x pOH = 6 pH = 8 Ex:.0001M NaOH = 1 x pOH = 4 pH = 10

Kw If you know the concentration of one ion you can find the other! [H+] x [OH-] = 1 x This is called the Kw Or the “ion product” of water.

So what is the [OH-] is the [H+] is.001M? So what is the [OH-] is the [H+] is.001M? [1 x ] x [OH-] = 1 x [OH-] = 1 x Everything keeps adding up to 14!! What’s up with that?

Let’s Try It You have a.001 HCl solution. Find: [H+], [OH-], pH, pOH

Let’s Try It You have a M NaOH solution. Find: [H+], [OH-], pH, pOH

Equation Summary pH = -log [H + ]pOH = -log [OH - ] [H + ] = 10 -pH [OH - ] = 10 -pOH pH + pOH = 14[H + ] x [OH - ] = 1x Acidic solution: pH 7 Neutral solution: pH = 7pOH = 7 Basic solution: pH > 7pOH 7pOH < 7

pH and pOH game pH and pOH game

Honors Questions If the pH of a solution is 3.25 find the pOH, [H+], and [OH-]. If.065 mole of KOH is placed in 20 liters of water, what is the resulting pH?

Acid Rain (Not to be confused with “Chocolate Rain”)

Acid Rain Unpolluted rain has a pH of 5.6 Unpolluted rain has a pH of 5.6 It is naturally acidic due to the gases in the air that dissolve in it. It is naturally acidic due to the gases in the air that dissolve in it.

Acid Rain Rain with a pH below 5.6 is “acid rain“ Rain with a pH below 5.6 is “acid rain“

pH of Rainwater across United States in 2001

Sources of Acid Rain

Power stations Power stations Oil refineries Oil refineries Coal with high S content Coal with high S content Car and truck emissions Car and truck emissions Bacterial decomposition, and lightning hitting N 2 Bacterial decomposition, and lightning hitting N 2

CO 2 in the air forms carbonic acid CO 2 in the air forms carbonic acid CO 2 + H 2 O H 2 CO 3 This increases the [H + ] of rain This increases the [H + ] of rain H 2 CO 3 H + (aq) + HCO 3 -(aq) Reactions with oxygen in air form SO 3 Reactions with oxygen in air form SO 3 2SO 2 + O 2 2 SO 3 Reactions with water in air form acids Reactions with water in air form acids SO 3 + H 2 O H 2 SO 4 sulfuric acid NO + H 2 O HNO 2 nitrous acid HNO 2 + H 2 O HNO 3 nitric acid HNO 2 + H 2 O HNO 3 nitric acid

Effects of Acid Rain

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

Acid Rain Destroys National Monuments rain-eating-washington-dc.html rain-eating-washington-dc.html Global Warming: CO 2 and Ocean Acidity -august-acid-in-the-water.html -august-acid-in-the-water.html

Acid Rain Site produced by EPA Acid Rain Site produced by EPA _kids/ _kids/ _kids/ _kids/ EPA Website Detailing Acid Rain Causes and Effects as well as Legislation EPA Website Detailing Acid Rain Causes and Effects as well as Legislation

Neutralization Reactions

General Reaction

Neutralization Forms Water H + + OH -  H 2 O H + + OH -  H 2 O from acid from base neutral from acid from base neutral This “net” reaction for neutralization is found on Table I. It is an exothermic reaction.

Forming a Salt (+) cation from the base, (-) anion from the acid combine to form a salt. HCl + NaOH NaCl + HOH Acid + Base Salt + water

Neutralization Reactions These are double replacement reactions Ions switch partners. Water is formed.

Neutralization Reactions If equal concentrations of hydrogen ion H + and hydroxide ions OH - are mixed, it results in a neutral solution. Ex:.1M LiOH +.1M HCl = Neutral Solution

Completing and Balancing and Naming Write charges for ions in acid and base. Write charges for ions in acid and base. Switch ion partners. (+ ions stay in front!!) Switch ion partners. (+ ions stay in front!!) Do not bring over subscripts except if part of a polyatomic ion! Do not bring over subscripts except if part of a polyatomic ion! Criss-Cross charges to balance formulas. Criss-Cross charges to balance formulas. Balance entire equation. Balance entire equation. Name the acid, base and salt. Name the acid, base and salt.

You Try It Complete and balance formulas and equation. Complete and balance formulas and equation. Name acid base and salt Name acid base and salt Ex:KOH + H 2 SO 4 Ex: Mg(OH) 2 + HNO 3

Titrations Purpose: To determine the concentration of an acid or base through a neutralization reaction.

Acid/Base Titration Buret is filled with a “standard solution” of known concentration. Erlenmeyer Flask contains solution of unknown conc.. Indicator (phenolphthalein) added to the flask.

Acid/Base Titrations Slowly “titrate” or drip liquid into flask from buret until indicator changes color. This is the “endpoint”. Record total volume used from buret.

Titration Formula M x V = M x V M A x V A = M B x V B Molarity Acid x Volume Acid = Molarity Base x Volume Base At “equivalence point” Moles H + = Moles OH -

Important Note Multiply acid/base side of equation by number of H + or OH - ions it produces when dissociating!!! Multiply acid/base side of equation by number of H + or OH - ions it produces when dissociating!!! Ex: Ex: H 2 SO 4 produces 2 H + so you would multiply the acid side by “2”

You Try It! A 50 ml sample of.2M HCl is neutralized by 75ml of NaOH. What is the conc. of the base? HCl NaOH HCl NaOH.2M x 50ml = M B x 75ml.2M x 50ml = M B x 75ml M B =.13M

You Try It! How much of a.1M H 2 SO 4 solution is needed to neutralize 50 ml of a.05 KOH solution? H 2 SO 4 KOH H 2 SO 4 KOH 2 x.1M x V A =.05M x 50ml 2 x.1M x V A =.05M x 50ml V A = 12.5 ml

Titration Applet ctions/projectfolder/flashfiles/stoichiometry /acid_base.html ctions/projectfolder/flashfiles/stoichiometry /acid_base.html

Hydrolysis Opposite reaction to neutralization Opposite reaction to neutralization Salt + Water Acid + Base

Parent Acid/Base If you know the salt involved you should be able to determine which acid and base it would form if water is added. If you know the salt involved you should be able to determine which acid and base it would form if water is added. Salt + Water Acid + Base Ex: NaCl with water (HOH) would form HCl and NaOH

You Try It Name the “parent” acid and base that would be produced from these salts. Name the “parent” acid and base that would be produced from these salts. Ex:Potassium chloride Ex:Potassium chloride Magnesium carbonate

pH and Hydrolysis Salts can yield neutral, acidic or basic solutions depending on what type of acid or base they produce. Salts can yield neutral, acidic or basic solutions depending on what type of acid or base they produce. SA/SB = Neutral SA/WB = Acidic WA/SB = Basic WA/WB = Undetermined

Strength of Acids and Bases Do they ionize 100%?

Strong Acids :Give up H + easily Dissociate completely (100%) in water HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 4, HClO 3

Weak acids: (all others) Hold onto H + Few molecules dissociate Ex: HCH 3 O 2 Ex: HC 2 H 3 O 2

HA Let’s examine the behavior of an acid, HA, in aqueous solution. What happens to the HA molecules in solution?

HA H+H+ A-A- Strong Acid 100% dissociation of HA Would the solution be conductive? Oh yeah…

HA H+H+ A-A- Weak Acid Partial dissociation of HA Would the solution be conductive? Not really…

HA H+H+ A-A- Weak Acid HA  H + + A - At any one time, only a fraction of the molecules are dissociated.

Acids Ionizing in Water (Strong vs. Weak) Acid H Transfer (Strong vs. Weak) htm htm

Strong Bases: Dissociate completely (100%) in water - Group I metal hydroxides (NaOH, LiOH, etc.) - Group I metal hydroxides (NaOH, LiOH, etc.) - Some Group II metal hydroxides - Some Group II metal hydroxides Ca(OH) 2, Ba(OH) 2, Sr(OH) 2 Weak Bases Only a few ions dissociate Ex: NH 3 (ammonia)

Strength and Reactivity Acids/bases of the same initial molar concentration can react differently and conduct electricity differently if one is weak and the other strong. Acids/bases of the same initial molar concentration can react differently and conduct electricity differently if one is weak and the other strong. Ex: 2M HCl = Strong Acid, Ex: 2M HCl = Strong Acid, very conductive very reactive 2M HC 2 H 3 O 2 = Weak Acid Weak Conduction Salad Dressing!!!

The Brønsted-Lowry Definition of Acids and Bases Acid:PROTON DONOR can donate H + ions. Base:PROTON ACCEPTOR accepts H + ions. Broader Definition than Arrhenius

Review: Arrhenius Definition of Acids and Bases Acids produce H + in aqueous (water) solutions Acids produce H + in aqueous (water) solutions water water HCl H + (aq) + Cl - (aq) Bases produce OH - in aqueous (water) solutions Bases produce OH - in aqueous (water) solutions water water NaOH Na + (aq) + OH - (aq) NaOH Na + (aq) + OH - (aq)

H + Transfer Acid/base reactions involve “proton transfer”. The reaction need not occur in water.

H + leaves one compound and is transferred to another. H + leaves one compound and is transferred to another. Ex: NH 3 + H 2 O NH OH - BaseAcid

Conjugate acid/base pairs: formulas differ by only a hydrogen ion, H +. The acid on one side becomes the base on the other side and vice versa. Ex: HCl + H 2 O H 3 O + + Cl - Acid BaseAcid Base

Conjugate acid contains one more H + in its formula

Amphoteric/Amphiprotic Substances: Can act as either an acid or a base. Must have an “H” in formula (to donate) Must have a free e - pair (to accept a H + )

Water is amphoteric Water is amphoteric It can donate an H + or accept an H +. It can donate an H + or accept an H +. It depends on what it is combined with. It depends on what it is combined with.

Water donates H + to NH 3 forming the hydroxide ion (OH - ). Water accepts H + from HCl forming the hydronium ion (H 3 O + ).

When life goes either way amphoteric (amphiprotic) substances HCO 3 - H 2 CO 3 CO H + - H + Acting like a base Acting like an acid accepts H + donates H +

Dilution water (solvent)solute concentrated, M initial diluted, M final adding water lowers the solute concentration moles of solute remain constant V initial V final moles initial = moles final M final x V final = M initial x V initial

Titration Applet l l Strong/Weak Acid Animation Acid dissociation in water Acid dissociation in water Acid/Bases Theories Acid/Bases Theories Titration Game Titration Game Acid Bases Hydrogen Transfer (Neutralization) Acid Bases Hydrogen Transfer (Neutralization)