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Chemistry

Atomic Origins

2015-08-14

www.njctl.org

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Acids and Bases

lactic acid lactate

Lactic acid is one of many metabolities produced when

we exercise. It generally loses an H+ ion to from the lactate ion (one of the chemicals that causes burning sensations in

our muscles.)

-

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Auto-ionization of WaterIn any sample of water, a small number of water molecules will

dissociate into H+ and OH- ions.

H

H

O OH

H

+-

H2O(l) -------> OH-(aq) + H+(aq)

- +The H+ ion then typically binds to a lone pair of electrons on another water molecule to make the hydronium ion: H3O+

2H2O(l) -------> OH-(aq) + H3O+(aq)

H

H

O OH H

- +H

HOH

H

O

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In 1909, a device was invented that could

measure the H+ or H3O+ concentration in an

aqueous solution.

H3O+(aq) = 1.0 x 10 -7 M

@ 25 C

Using this data, the equilibrium constant for the auto-ionization of water can be calculated.

2H2O(l) --> H3O+(aq) + OH-(aq)

Recalling our equilibrium concepts...... Kw = [H3O+][OH-]

Since equal amounts of H3O+ and OH- are created...

[H3O+] = [OH-] = 1.0 x 10 -7 M

Kw = (1.0 x 10 -7)(1.0 x 10 -7) = 1.0 x 10 -14 M

Auto-ionization of Water

Clearly, the equilibrium lies far to the left!

Water does NOT like to dissociate.

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1 What is the concentration of hydronium ions (H3O+) in pure water?

A 1.0 x 10 -2 M

B 1.0 x 10-5 M

C 1.0 x 10-7 M

D 1.0 x 10 -10 M

E 1.0 x 10-14 M

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2 Which of the following is the value of Kw for water?A 1.0 x 10-2

B 1.0 x 10-4

C 1.0 x 10-7

D 1.0 x 10-9

E 1.0 x 10-14

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3 Which of the following would be true in pure water?A [H3O+] = [OH-]

B [H3O+] < [OH-]

C [OH-] = 1 x10-7 M

D A and C

E B and C

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4 The magnitude of K w indicates that _________

A water ionizes to a very small extentB the autoionization of water is exothermicC water ionizes very quicklyD water ionizes very slowly

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5 The molar concentration of hydronium ion, [H3O+ ], in pure water at 25 °C is ___________.

A 0B 1

C 7

D 10-7

E 10-14

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Calculating H3O+ or OH- In the natural world, we do not find pure water. There are always

things dissolved in it that influence the concentrations of hydronium and hydroxide ions.

The hydronium or hydroxide concentration in a solution can be determined easily if one knows one or the other.

Kw = [H3O+][OH-] = 1.0 x 10-14

Rearranged for [H3O+] Rearranged for [OH-]

[H3O+] = 1.0 x 10-14/[OH-] [OH-] = 1.0 x 10-14/[H3O+]

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Kw = [H3O+][OH-] rearranged to find [OH-] = Kw/[H3O+]

= 1.0 x 10-14/ 3.4 x 10-5 = 2.9 x 10-10 = [OH-]

Kw = [H3O+][OH-] rearranged to find [H3O+] = Kw/[OH-]

= 1.0 x 10-14/ 1.2 x 10-12 = 8.3 x 10-3 = [H3O+]

#1 What is the [OH-] in a solution with [H3O+] = 3.4 x 10-5 M?

#2 What is the [H3O+] in a solution with [OH-] = 1.2 x 10-12

Calculating H3O+ or OH- Let's do some examples!

move for answer

move for answer

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Calculating H3O+ or OH- Application:

Tap water is NOT pure water. There are many things dissolved in it that affect the amount of [H3O+] and [OH-] in the water sample. Can you think of some things that might chloride (Cl-), carbonate (CO3

2-)

be dissolved in tap water?

Flouride (F-), calcium ions (Ca2+), c

The average concentration of H3O+ in New York City tap water is

5.01 x 10-8 M. What is the average [OH-]?

Kw = [H3O+][OH-] rearranged to find [OH-]

= Kw/[H3O+]

= 1.0 x 10-14/5.01x 10-8

= 1.99x 10-7 M

move for answer

move for answer

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6 What is the [H3O+] in an aqueous sample with an [OH-] equal to 3.4 x 10-3 M?

A 3.4 x 10-3 MB 2.9 x 10-12 M

C 1.0 x 10-7 M

D 9.4 x 10-7 M

E 3.4 x 1011 M

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7 Which of the following would have the smallest [OH-]?

A solution with [H3O+] = 2.4 x 10-1

B solution with [H3O+] = 2.4 x 10-11

C solution with [H3O+] = 2.4 x 10-6

D solution with [OH-] = 2.4 x 10-3

E solution with [OH-] = 2.4 x 10-12

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8 The pacific ocean off the coast of Hawaii has

a [OH-] = 8.32 x 10-9 M.

What is the [H3O+]?

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Arrhenius Definition of Acids and Bases

As we have learned, when certain substances are added to water, the H3O+ concentration changes.

Furthermore, if the [H3O+] changes, it would influence the [OH-].

Kw = [H3O+] [OH-] = 1.0x 10-14

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In 1884, Swedish scientist Svante Arrhenius decided to

create definitions for substances that changed the [H3O+] in an

aqueous solution.

Arrhenius Definition of Acids and Bases

Arrhenius labeled anything that increased the [H3O+] an acid

Arrhenius labeled anything that increased the [OH-] a base

By measuring the [H3O+] of a water solution after a substance had been added, he could see if the substance was acidic or basic!

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H3O+(aq) = 2.3x 10-6 M @ 25 C

HCN(aq)

Example 1: Let's add some HCN(aq)

Remember that pure water has an [H3O+] = 1.0 X 10-7M.

Since the [H3O+] is higher than 1.0 X 10-7M, Arrhenius would have described HCN as an acid!

Arrhenius Definition of Acids and Bases

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By measuring the [H3O+] of a water solution after a substance had been added, he could see if the substance was acidic or basic!

H3O+(aq) = 4.1x10-11 M @ 25 C

NaOH(s)

Example 2: Let's add some NaOH(s)

Since the [H3O+] is lower than 1.0 x 10-7 M thereby making the [OH-] higher than 1.0 x 10-7M, Arrhenius would have described

NaOH as a base!

Arrhenius Definition of Acids and Bases

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9 Which of the following solutions would be considered by Arrhenius to be the most basic?

A 0.1 M NH3 [H3O+] = 3.4x10-10 M

B 0.1 M NaOH [H3O+]= 1x10-13M

C 0.1 M HCl [H3O+] =1x10-1 M

D 0.1 M HCN [H3O+]= 2.3x10-6M

E Pure water [H3O+]=1x10-7 M answ

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10 Vinegar has a [H3O+] of around 3.4 x10-3 M. Which of the following solutions would be considered by Arrhenius to be MORE acidic than vinegar?

A 0.1 M NaOH [H3O+] = 1x10-13 M

B 0.1 M HCl [OH-] =1.0 x10-13 M

C 0.1 M NaCN [OH-] = 2.6x10-4 M

D 0.1 M NH3 [H3O+] = 7.6x10-9 M

E pure water [OH-] = 1.0 x10-7 M

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Bronsted Lowry Definition of an Acid

At this time, most scientists explained Arrhenius acids as possessing H+ ions that could be added to water to produce [H3O+]

Arrhenius acids in action

HF(aq) + H2O(l) --> F-(aq) + H3O+(aq)

Here, the hydroflouric acid (HF) donates one of it's H+ ions to a water molecule increasing the [H3O+](aq)

Two scientists - Bronsted and Lowry, working independently, decided a more appropriate definition of an acid would be that of an H+ donor.

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Bronsted/Lowry Definition of Base

At this time, most scientists explained Arrhenius bases as possessing OH- ions that would increase the [OH-] and decrease the [H3O+].

NaOH(aq) --> Na+(aq) + OH-(aq)

[OH-] causes [H3O+]

Arrhenius base in action

Unfortunately, this view required that all bases had to possess the hydroxide ion. This was clearly not the case. Many substances, like ammonia (NH3) or sodium phosphate (Na3PO4), were known to be

basic but did NOT have any hydroxide ions!

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Bronsted Lowry Definition of Base

Bronsted and Lowry proposed that, insteading of possessing hydroxide ions, a base was a substance that accepted an H+ from

water to produce OH- ions!

NH3(g) + H2O(l) --> NH4+(aq) + OH-(aq)

Bronsted base in action

When ammonia, NH3, accepts the H+ from the water, the water turns into OH- making the solution basic.

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Bronsted Lowry Definition of Acid and Bases

Summary

Acids are defined as H+ (proton) donors.

HC3H6O3(aq) + H2O(l) --> C3H6O3-(aq) + H3O+(aq)

lactic acid

cyanide base

Bases are defined as H+ (proton) acceptors.

CN-(aq) + H2O(l) --> HCN(aq) + OH-(aq)

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11 A Bronsted acid is a substance that...

A accepts H+ ions

B donates OH- ions

C increases the concentration of OH- ions

D donates H+ ions

E accepts OH- ions

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12 Which of the following could NOT act as a Bronsted acid?

A HCN

B H2 SO4

C NH4 +

D H3 O+

E BF3

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13 A Bronsted-Lowry base is defined as a substance that __________.

A increases [H+ ] when placed in H2 O

B decreases [H+ ] when placed in H2 O

C increases [OH-] when placed in H2 O

D acts as a proton acceptor

E acts as a proton donor

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14 Which of the following compounds could never act as a Bronsted acid? A SO4

2-

B HSO4-

C H2 SO4

D NH3

E CH3 COOH

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Bronsted Acids and Bases (In Depth)

Acids and Bases go togetherIt should be noted that if an acid donates an H+, that H+ will be

accepted by another substance.So, where there is an acid, there will be a base

N

H

H

H

OH

H

N

H

H

H

H O

H+ +

NH3 acts as a base and accepts an H+ to become NH4+

water acts an acid and donates it's H+ to become OH-

+ -

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Bronsted Acids and Bases (In Depth)Identifying an acid or a base

By examining the products and reactants of a chemical reaction, one can identify if a substance is behaving as an acid or as a

base.

ExampleHSO4 -(aq) + CN-(aq) --> SO4

2- (aq) + HCN(aq)

HSO4 -(aq) donated an H+ to become SO42- = It's an acid!

CN-(aq) accepted an H+ to become HCN = It's a base!

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Bronsted Acids and Bases (In Depth)

Identifying an acid or a base

Identify which reactant behaves as an acid and which behaves as a base in the following reaction!

H2 O(l) + CH3 NH3+(aq) --> CH3 NH2 (aq) + H3 O+(aq)

CH3 NH3+(aq) donated an H+ to become CH3 NH2 = It's an acid!

H2O(aq) accepted an H+ to become H3O+ = It's a base!move for answer

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15 According to the following reaction, which reactant molecule is acting as an acid?

A H2 SO4

B H2 O

C H3 O+

D HSO4-

E None of the above

H2 O + H2 SO4 → H3 O+ + HSO4 -

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16 According to the following reaction, which reactant molecule is acting as a base?

H2 O + H2 SO4 → H3 O+ + HSO4 -

A H2 SO4

B H2 O

C H3 O+

D HSO4-

E None of the above

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Slide 36 / 12317 According to the following reaction, which reactant

molecule is acting as a base?

H3 O+ + HSO4 - → H2 O + H2 SO4

A H2 SO4

B H2 O

C H3 O+

D HSO4-

E None of the above

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18 For the following reaction, identify whether the circled compound is behaving as an acid or a base.

A Acid

B Base

C Neither

D Both

E None of the above

H3 PO4 + H2 O ⇌ H2 PO4 - + H3 O+

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19 For the following reaction, identify whether the circled compound is behaving as an acid or a base.

H3 PO4 + H2 O ⇌ H2 PO4 - + H3 O+

A Acid

B Base

C Neither

D Both

E None of the above

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Bronsted Acids and Bases (In Depth)

Identifying an acid or a base in reversible reactions

Reactions are reversible so we must be able to identify acids and bases based on the reverse reaction.

ExampleF-(aq) + H2 O(l) <--> HF(aq) + OH-(aq)

HF(aq) donates an H+ ion to become F-(aq) = It's an acidOH-(aq) accepts an H+ to become H2 O(l) = It's a base

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20 For the following reaction, identify whether the circled compound is behaving as an acid or a base.

H3 PO4 + H2 O ⇌ H2 PO4 - + H3 O+

A Acid

B Base

C Neither

D Both

E None of the above

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21 For the following reaction, identify whether the circled compound is behaving as an acid or a base.

H3 PO4 + H2 O ⇌ H2 PO4 - + H3 O+

A Acid

B Base

C Neither

D Both

E None of the above

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Conjugate Acids and Bases

The term conjugate comes from the Latin word “conjugare,” meaning “to join together.”

Reactions between acids and bases always yield their conjugate bases and acids.

HNO2(aq) + H2O(l) NO2 - (aq) + H3O+(aq)

donates H+

accepts H+

Acid Base Conjugate base

conjugate acid

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Conjugate Acids and Bases

To find an acid or bases conjugate in a reaction, simply write the formula for the substance left after the H+ has been donated or

accepted.

Example: What is the conjugate base of HSO4 -(aq)?Since we are looking for a conjugate base, HSO4

- must be an acid so let's have it donate an H+

HSO4-(aq) --> SO4

2- (aq) + H+(aq)

conjugate base

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Conjugate Acids and Bases

Example: What is the conjugate acid of CO3 2- (aq)?Since we are looking for a conjugate acid, CO3

2- must be a base so let's have it accept an H+CO3

2- (aq) + H+ --> HCO3-(aq)

conjugate acid

Dealing with chargesIf you accept an H+, you become more positiveIf you donate an H+, you become more negative

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22 Which of the following would be the conjugate base of HNO2 ?

A NO2-

B H2 NO2

C NO2

D NO22-

E HNO2

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23 Which would be the conjugate acid of HCO3 -(aq)?

A CO32-

B HCO3

C CO3

D H2 CO3-

E H2 CO3

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24 What would be the an acid/conjugate pair in the following reaction?

A NH2 -/H2 O

B NH2 -/NH3

C H2 O/OH-

D H2 O/NH3

E None of these

NH2 - + H2 O --> NH3 + OH-

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Lewis Acids and Bases

DefinitionScientists noticed that some substances could create acidic

solutions despite not having any H+ ions to donate. An example of this was the Ca2+ ion.

G.N. Lewis proposed a mechanism for this

Ca2+ + ---> Ca (OH)+ + +

O

H

H

H

The metal ion accepted a pair of electrons from the water molecule, resulting in the donation of one of the

water's H+ ions.

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Lewis Acids and Bases

A Lewis acid is an electron pair acceptor. Metal ions or molecules with incomplete octets (BF3 ) are good examples.

A Lewis base is an electron pair donor. Molecules with unbonded electrons (NH3 , CN-, OH-, H2 O) are good examples.

Lewis Acid (e- pair

acceptor)

Lewis Base (e- pair donor)

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25 A lewis base is a substance that...

A Accepts H+ ions

B Donates H+ ions

C Accepts e- pairs

D Donates e- pairs

E Decreases the concentration of [OH-]

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26 Which of the following would likely act as a lewis acid?

A NH3

B OH-C CN-

D H2OE Fe3+

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What are Acids and Bases?

Definition Type Acid Base

Arrhenius (traditional)substance that produces

H3O+ ions in aqueous solution

substance that decreases H3O+ ions in aqueous

solution

Bronsted -Lowry substance that donates H+ ions in reaction

substance that accepts H+ ions in reaction

Lewis substance that accepts an electron pair in reaction

substance that donates an electron pair in reaction

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Question 1: Can you think why the Arrhenius definition was considered insuffienct?

It could not explain how a substance without hydroxide could make a solution basic

Question 2: Can you explain why Lewis felt that the Bronsted definition was insufficient?

It required an acid to be in possession of a hydrogen atom.move for answer

move for answer

Class Discussion - Evolution of a definition

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What are Acids and Bases?

All acids are Lewis acids, most are also Bronsted acids, and many are Arrhenius acids

Lewis

Bronsted

Arrhenius

The lewis definition is generally considered the most broad.

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If a substance can act both as an acid and base, it is known as amphoteric. For example, water can act as a base or acid depending on the situation.

Amphoteric Substances

HCl + H2O Cl- + H3O+

Above, water accepts a proton, thus acting as a base.

NH3 +H2O NH4 + + OH-

Above, water donates a proton, thus acting as an acid

Because of water's amphoteric nature, it makes the perfect solvent for most acid base reactions. Its nature allows for easier

exchange of protons between acids and bases.

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Acid and Base Strength

Strong acids are completely ionized in water (They all donate their H+ ions).

Their conjugate bases are very weak. StrongWeakNegligible StrongWeakNegligible

Acid Base

HCl Cl -

H2SO4 HSO 4-

HNO3 NO 3-

H3O+ H 2OHSO4

- SO 42-

H3PO4 H2PO4-

HF F-HC2H3O2 C2H3O2

-

H2CO3 HCO 3-

H2S HS -

H2PO4- HPO 4

2-

NH4+ NH 3

HCO3- CO 3

2-

HPO42- PO 4

3-

H2O OH -

OH- O 2-

H2 H -

CH4 CH 3-

100% protonatedin H2O

Bas

e st

reng

th in

crea

ses

Aci

d st

reng

th in

crea

ses

100% ionized in H2O

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Acid and Base Strength

Weak acids only ionize partially in water.

Their conjugate bases are weak bases.

StrongWeakNegligible StrongWeakNegligible

Acid Base

HCl Cl -

H2SO4 HSO 4-

HNO3 NO 3-

H3O+ H 2OHSO4

- SO 42-

H3PO4 H2PO4-

HF F-HC2H3O2 C2H3O2

-

H2CO3 HCO 3-

H2S HS -

H2PO4- HPO 4

2-

NH4+ NH 3

HCO3- CO 3

2-

HPO42- PO 4

3-

H2O OH -

OH- O 2-

H2 H -

CH4 CH 3-

100% protonatedin H2O

Bas

e st

reng

th in

crea

ses

Aci

d st

reng

th in

crea

ses

100% ionized in H2O

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Substances with negligible acidity do not ionize in water. They will not readily give up protons.

Their conjugate bases are exceedingly strong.

Acid and Base Strength

StrongWeakNegligibleStrongWeakNegligible

Acid Base

HCl Cl -

H2SO4 HSO 4-

HNO3 NO 3-

H3O+ H 2OHSO4

- SO 42-

H3PO4 H2PO4-

HF F-HC2H3O2 C2H3O2

-

H2CO3 HCO 3-

H2S HS -

H2PO4- HPO 4

2-

NH4+ NH 3

HCO3- CO 3

2-

HPO42- PO 4

3-

H2O OH -

OH- O 2-

H2 H -

CH4 CH 3-

100% protonatedin H2O

Bas

e st

reng

th in

crea

ses

Aci

d st

reng

th in

crea

ses

100% ionized in H2O

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Strong Acids

There are seven strong acids:3 contain a H bound to the very electronegative halogens:

HCl hydrochloric acidHBr hydrobromic acidHI hydroiodic acid

HF, or hydrofloric acid, is a weak acid. Although flourine is very electronegative, the bond strength between flourine and hydrogen is too strong for HF to easily give up H+ .

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27 Which of the following is NOT a strong acid?

A HBr

B HFC HI

D HCl

E A and C

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Strong AcidsThere are seven strong acids:4 are from the very electron drawing oxyanions:

HNO3 nitric acidH2SO4 sulfuric acidHClO3 chloric acid HClO4 perchloric acid

Each of these anions has a central atom that is highly electronegative compared to hydrogen. The oxygens that are bonded to that central atom draw more electrons from it making it even more electronegative and likely to take electrons from hydrogen forming H+ .

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Strong Acids

The seven strong acids are:

HCl hydrochloric acidHBr hydrobromic acidHI hydroiodic acid

HNO3 nitric acidH2SO4 sulfuric acidHClO3 chloric acid HClO4 perchloric acid

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Monoprotic Acids

The seven strong acids are strong electrolytes because they are 100% ionized. In other words, these compounds exist totally as ions in aqueous solution.

For the monoprotic strong acids (acids that donates only one proton per molecule of the acid), the hydronium ion concentration equals the acid concentration.

[H3O+] = [acid]

So, if you have a solution of 0.5 M HCl, then [H3O+] = 0.5 M

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All alkali metals in Group I form hydroxides that are strong bases: LiOH, NaOH, KOH, etc.

Only the heavier alkaline earth metals in Group II form strong bases: Ca(OH)2 , Sr(OH)2 , and Ba(OH)2 .

Again, these substances dissociate completely in aqueous solution. In other words, NaOH exists entirely as Na+ ions and OH- ions in water.

Strong Bases

All strong bases are group of compounds called "metal hydroxides."

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28 What would be the [H3O+] in a 0.005 M HBr solution?

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In any acid-base reaction, the proton moves toward the stronger base. In other words, a stronger base will "hold onto" its proton whereas a strong acid easily releases its proton(s).

HCl(aq) + H2O(l) --> H3O+(aq) + Cl-(aq)

acid base conj. acid conj. base

H2O is a much stronger base than Cl-, so the proton

moves from HCl to H2O.

Acid and Base Strength

WeakNegligibleStrongWeakNegligible

Acid Base

HCl Cl -

H2SO4 HSO 4-

HNO3 NO 3-

H3O+ H 2OHSO4

- SO 42-

H3PO4 H2PO4-

HF F-HC2H3O2 C2H3O2

-

H2CO3 HCO 3-

H2S HS -

H2PO4- HPO 4

2-

NH4+ NH 3

HCO3- CO 3

2-

HPO42- PO 4

3-

H2O OH -

OH- O 2-

H2 H -

CH4 CH 3-

100% protonatedin H2O

Bas

e st

reng

th in

crea

ses

Aci

d st

reng

th in

crea

ses

100% ionized in H2O

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29 What would be the [OH-] in a 0.034 M NaOH solution?

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CH3CO2H(aq) + H2O(l) H3O+(aq) + CH3CO2-(aq)

Acetic acid is a weak acid. This means that only a small percent of the acid will dissociate.

The double headed arrow is used only in weak acid or weak base dissociation equations since the reaction can proceed with both the forward and reverse reactions.

Acid and Base Strength

A single arrow is used for strong acid or strong bases which dissociate completely since the forward reaction is much more favorable than the reverse reaction.

NaOH Na+ (aq) + OH- (aq)

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30 Strong acids have ___________ conjugate bases.

A strongB weakC neutralD negative

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31 HBr, hydrobromic acid is a strong acid. This means that _______________.

A aqueous solutions of HBr contain equal concentrations of H+ and OH-

B does not dissociate at all when it is dissolved in water

C cannot be neutralized by a base

D dissociates completely to H+ and Br- when it dissolves in water

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pH pH is defined as the negative

base-10 logarithm of the concentration of hydronium ion.

pH = -log [H3O+]

It is a measure of hydrogen ion concentration, [H+ ] in a solution,

where the concentration is measured in moles H+ per liter, or molarity.

The pH scale ranges from 0-14.

Generally when calculating pH we round to two decimal places.

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What is the pH of the solution with hydrogen ion concentration of 5.67x10-8 M (molar)?

pH = -log [H+]

First, take the log of 5.67x10-8 = -7.25 Now, change the sign from - to +

Answer: pH = 7.25

Calculating pH

Note: If you take the log of

-5.67x10-8 M, you will end up

with an incorrect answer.

The order of operations:

1. Take the log

2. Switch the sign

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32 What is the pH of a solution with hydrogen ion concentration of 1.0 x 10-5 M?

A 1.0 x 10-5

B -5.00C 5.00

D 9.00

E -9.00

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33 What is the pH of a solution with hydrogen ion concentration of 1.0 x 10-12 M?

A 1.0 x 10-12

B 12.00

C 2.00

D -12.00

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34 What is the pH of a solution whose hydronium ion concentration is 7.14 x 10-3 M?

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35 What is the pH of a solution whose hydronium ion concentration is 1.92 x 10-9 M?

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36 What is the pH of a 0.34 M solution of the strong acid HI? (Remember that strong acids ionize completely)

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pHApplication

In order for proteins to be digested in the stomach, the pH must be lower than 2.7. If the pH is too high, proteins will not be broken

down and may cause a food allergy or indigestion.

A patient complains of indigestion and a sample of stomach fluid is taken and the [H3 O+] is found to

be 3.4 X10-3 M. Is there a problem with the pH?

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What is the relationship between [H3O+] and the pH value?

Below are three different [H3 O+]. Find the pH of each. pH = -log [H3O+]

pH

Hydrogen ion concentration, [H3O+]in moles/Liter pH

1.0 x 10-1

1.0 x 10-2

1.0 x 10-10

Clearly, the lower the [H3O+], the _____ the pH.

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What is the relationship between [H3 O+], the pH value, and the acidity and basicity of a solution?

pH

low H3 O+

High H3 O+

high OH-

low OH-

acidic acid

icba

sicbasic

neutral

Slide 82 / 123

pH

These are the pH values for several common substances.

Mor

e ac

idic

Mor

e ba

sic

Battery acid

lemon juice

pure rain or water

distilled water

sea waterbaking soda

household ammonia

household bleach

household lye

gastric fluid

carbonated beveragesvinegarorange juice

beercoffeeegg yolksmilk

blood

milk of magnesia

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For more accurate measurements, one uses a pH meter, which measures the voltage in the solution.

How Do We Measure pH?

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How Do We Measure pH?For less accurate measurements, one can use Litmus paper

“Red” paper turns blue above ~pH = 8“Blue” paper turns red below ~pH = 5

Or an indicator (usually an organic dye)

0 2 4 6 8 10 12 14

pH range for color change

Methyl violet

Thymol blue

Methyl orange

Bromothymol blue

Phenolphthalein

Alizarin yellow R

Methyl red

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pH

Solution type [H +](M) [OH-] (M) pH value

Acidic > 1.0x10-7 <1.0x10-7 <7.00Neutral =1.0x10-7 =1.0x10-7 =7.00Basic <1.0x10-7 > 1.0x10-7 >7.00

[H+] > [OH-]There are excess hydrogen ions in

solution.

[H+] < [OH-]There are excess hydroxide ions in

solution.

BASEACID

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37 Which of the following solutions would be most acidic?A pH = 3

B pH = 2

C pH = 11

D pH = 14

E pH = 1

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38 Which of the following (M) solutions would be LEAST acidic?

A [H3 O+] = 2.3x10-7

B [H3O+] = 9.1x10-3

C [H3O+] = 1.3 x10-2

D [H3O+] = 7.8x10-9

E [H3O+] = 4.5x10-4

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39 Which of the following solutions would have the highest pH?

A [OH-] =3.4x10-3

B [H3O+] = 5.4x10-11

C [OH-] = 3.4x10-12

D [H3O+] =5.4x10-2

E [OH-] =3.4x10-1

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40 Which solution below has the highest concentration of hydroxide ions?

A pH = 3.21

B pH = 7.00

C pH = 8.93

D pH = 12.60

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41 Which solution below has the lowest concentration of hydrogen ions?

A pH = 11.40

B pH = 8.53

C pH = 5.91

D pH =1.98

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42 For a basic solution, the hydrogen ion concentration is ______________ than the hydroxide ion concentration.

A greater than

B less than

C equal to

D Not enough information.

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43 For an acidic solution, the hydroxide ion concentration is ______________ than the hydrogen ion concentration.

A greater than

B less than

C equal to

D Not enough information.

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44 Which of the following would turn blue litmus paper red?

A Solution with [OH-] = 2.3 E-7 M

B Solution with pH = 4

C Solution with pOH = 2

D A and C

E B and C

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Understanding a Log Based Scale

Because of the base-10 logarithm, each 1.0-point value on the pH scale differs by a value of ten.

A solution with pH = 9 has a hydrogen ion concentration, [H+],

that is 10 times more than a pH = 10 solution.

A solution with pH = 8 has a hydrogen ion concentration, [H+],

that is 102 or 100 times more than a pH = 10 solution.

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45 A solution with pH = 3 has a hydrogen ion concentration that is __________than a solution with pH = 5.

A 2x more

B 2x less

C 100x more

D 100x less

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46 A solution with pH = 14 has a hydrogen ion concentration that is __________than a solution with pH = 11.

A 3x more

B 3x less

C 1000x more

D 1000x less

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pOHJust as the pH of a solution can be calculated by:

pH = -log[H3O+]

The pOH of a solution can be calculated by:

pOH = - log[OH-]

Recall that the [OH-] and [H3O+] are inversly related so pH and pOH are as well.

0 7 14low pH

14 7 0

high pOH low pOH

high pH

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Calculating pOH

What is the pOH of a solution that has a [OH-] = 2.3 E-5 M?

pOH = - log[OH-]

pOH = - log(2.3 E-5)

= 4.63

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47 What is the pOH of a solution with a [OH-] = 2.7 x10-2 M?

A 2.7

B 12.43

C 1.57

D -1.57

E -2.7 answ

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pOHOnce we have calculated pOH, it is very easy to calculate pH.

Remember that our solvent for all of our reactions is Water. We also know that we have a Kw value for water of 1 x 10-14. This is ALWAYS true for water. We can also determine the following equations:

Kw=[H+][OH-]

Throwing in our logarithms for pH, pOH and pKw we end up with this:

pKw = pH + pOH

Remember that Kw is a constant and if we that the negative log of that constant we get 14 so.....

14 = pH + pOH

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pOH to pH and vice versa

Therefore, if we have a pOH and we want to convert it to pH, so long as we are using water for our solvent, we can use the below equation to determine the pH of the solution.

14 = pH + pOH

In other words, to find the pH of a basic compound, you first must need to determine the pOH of that compound and

then use that to determine the pH. Remember that pOH is calculated using [OH-] and pH is calculated using [H+].

Other then that, there is no difference in the steps used to calculate pOH and pH.

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48 What is the pOH of a solution with a pH =5?

A 5B 15C 7D 8E 9

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49 What is the pH of an aqueous ammonia solution with a [OH-] = 1 x 10-4 M?

A 4B 1 x10-4

C 10D 1 x10-10

E 3 answ

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50 What is the pOH of an aqueous HCl solution with a [H3O+] = 2.7 x10-1 M?

A 13.43

B 0.57

C 2.7 x10-1

D 2.7 x10+1

E 12.43

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51 What would be the pH of a 0.045 M NaOH solution? (Recall that NaOH is a strong base and will ionize completely)

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52 Which of the following would be LEAST acidic?

A pOH = 2

B pOH = 4

C pH = 10

D pH = 2

E pH = 11

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Calculating [H3O+] and [OH-] from pH or pOH

If given a pH, one can determine the [H3O+] by:

10-pH = [H3O+]

If given a pOH, one can determine the [OH-] by:

10-pOH = [OH-]

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Calculating [H3O+] and [OH-] from pH or pOH

What is the [H3O+] in a lemon juice solution with a pH = 3.5?

10-3.5 = 3.2x10-4 M

What is the [H3O+] in a bottle of soda with a pOH = 11.4?

14 = pOH + pH 14 = 11.4 + pH

pH = 2.6

10-2.6 = 2.5x10-3 M

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53 What is the OH- ion concentration if the pH of a solution is 6?

A 1 x10-6

B 1 x10-8

C 1 x106

D 1 x1012 answ

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54 What is the OH- concentration if the pH of a solution is 11?

A 1 x 10-4

B 1 x10-3

C 1 x 10-11

D 1 x1011

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55 What is the hydrogen ion concentration (M) in a solution of Milk of Magnesia whose pH = 9.8?

A 9.8 M

B 9.8x10-10 M

C 4.2 M

D 1.6x10-10 M

E 4.2x10-10 M

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56 What is the hydronium ion concentration in a solution whose pH = 4.29?

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57 For a 1.0-M solution of a strong acid, a reasonable pH would be_____.

A 0

B 6

C 7

D 9

E 13

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58 For a 1.0-M solution of a weak base, a reasonable pH would be_____.

A 2

B 6

C 7

D 9

E 14

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Buffers

A buffer is a solution that can maintain a nearly constant pH when diluted or when strong acids or strong bases are added to it.

A buffer solution is made up of a weak acid, HA, and its conjugate base, A-, or a weak base and its conjugate acid.

http://chemcollective .org/activities /tutoria ls /buffe rs /buffe rs3

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Buffers

When a strong base is added to a buffer the hydroxide OH- from the strong base reacts with the weak acid, which gives up its H+ to form water. The weak acid neutralizes the strong base.

http://chemcollective .org/activities /tutoria ls /buffe rs /buffe rs3

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BuffersIf a strong acid is added to a buffer it will react with the weak conjugate base to form a weak acid that does not readily dissociate, and, therefore, does not significantly alter the pH.

http://chemcollective .org/activities /tutoria ls /buffe rs /buffe rs3

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59 Buffers are composed of

A Strong acids to neutralize strong bases

B Strong bases to neutralize strong acids

C A weak acid and its conjugate base

D A strong acid and its conjugate base

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60 A buffer solution contains carbonic acid (H2CO3) and bicarbonate (HCO3-). When a small amount of HCl is added to the buffer

A The HCl dissociates and the H+ significantly lowers the pH of the solution.

B The HCl dissociates and the H+ reacts with the bicarbonate to form a neutral compound.

C The pH of the solution remains stable.

D Both b and c

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61 A buffer solution contains formic acid (HCO2H) and sodium formate (HCO2Na). When a small amount of NaOH is added to the buffer

A The NaOH dissociates and the OH- significantly raises the pH of the solution.

B The formic acid neutralizes the hydroxide to form water.

C The sodium formate neutralizes the hydroxide.

D None of the above

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Buffer systems maintain a constant pH in blood

The body maintains the pH of blood at around 7.4. If the pH level changes just a few tenths of a pH unit, serious health consequences can result. A decrease in blood pH is called acidosis, an increase is called alkalosis.

There are 3 systems that regulate the pH of blood. The bicarbonate system is the most important and is controlled by the rate of respiration. In the bicarbonate system, carbon dioxide combines with water to form carbonic acid, which dissociates to form bicarbonate and hydrogen ions. CO2 + H2O H2CO3 HCO3- + H+

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62 Based on the figure below, holding one's breath can lead to which condition?

A Alkalosis

B Acidosis

C Hemolysis

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63 How does the body's response to the condition in the previous question help restore the pH of the blood?

A Breathing out reduces the amount of CO2 present, thereby reducing the production of carbonic acid.

B Breathing in increases the amount of oxygen in the blood.

C Breathing has no effect on the pH of blood.