Acids vs. Bases: Chemical Counterparts

• Acid – a substance with a high amount of hydrogen ions (H+) present.

Hydrogen ions (H+) are also called protons.

Properties of Acids:1)Taste Sour2)Dissolves Substances3)Reacts with metals to form hydrogen gas (H2)

• Base– a substance with a high amount of hydroxide ions (OH-) present.

Properties of Bases:1)Tastes bitter.2)Feels filmy or slimy.3)Corrosive.

Corrosive – able to break down or dissolve certain substances.

Examples of Common Acids and Bases:

Lemon Juice (Acid) Lye (Base)

Ammonia (Base) Vinegar (Acid)

• There are two different theories describing the chemical characteristics of acids and bases:

1) Arrhenius Model – both give up ions. Svante Arrhenius (1859-1927)

Acids: a substance that gives a hydrogen ion (H+)

\` Bases: a substance that gives

up a hydroxide ion (OH-)

2) Bronsted – Lowry Model – acid and base work together chemically.

Acids: Acids give up (donate) a hydrogen ion (H+).

*same as Arrhenius definition*

Bases: Bases take in (accept) hydrogen ion (H+).

Johannes Bronsted

Thomas Lowry

The Arrhenius and Bronsted-Lowry definitions of acids and bases emphasize different aspects of acids and bases:

Arrhenius Bronsted - Lowry

Acid Gives off protons (H+)

Gives (donates) protons (H+)

Base Gives off hydroxide ions

(OH-)

Accepts

protons (H+)

Emphasis Ion given by the substance.

How acids and bases work together.

• Substances are described based on the ratio of hydrogen ions (H+) to hydroxide ions (OH-).

Acidic – Substance that acts like an acid.*Substance with a higher amount of

hydrogen ion (H+) than hydroxide ion (OH-).

Basic - Substance that acts like a base.*Substance with a higher amount of

hydroxide ion (OH-) than hydrogen ion (H+).

• Substances are described based on the ratio of hydrogen ions (H+) to hydroxide ions (OH-).

Neutral – Doesn’t act like acid or base.*Same amount of hydrogen ion (H+) and

hydroxide ion (OH-)

*Distilled water is neutral as it has an equal ratio of hydrogen ions (H+) and hydroxide ions (OH-).

Strong Acids Formula

Hydrochloric HCl

Hydrobromic HBr

Hydroiodic HI

Perchloric HClO3

Nitric HNO3

Sulfuric H2SO4

Sulfuric Acid – this is what makes you “cry” when you cut into an onion

Strong Bases Formula

Sodium Hydroxide NaOH

***Ammonia*** NH3

Baking Soda NaHCO3 or

NaCO2(OH)

Calcium Hydroxide Ca(OH)2

*Baking soda is used in labs to clean up acid spills*

• According to Arrhenius, ammonia (NH3) can’t be a base, but based on the Bronsted-Lowry

definition, it is a base.

Arrhenius Bronsted-Lowry Bases give OH- Bases accept H+

δ-H+

pH scale – A scale used to determine how strong of an acid or base a substance is.

- A scale that goes from 0-14 (14 is the highest)

Acids Neutral BasespH = 0-7 pH = 7 pH = 7-14

The lower pH = the stronger the acid The higher pH = the stronger the base

• Litmus paper – paper that will change color base the properties of the solution.

Acids – Turns Litmus paper red

Bases – Turns Litmus paper blue

***Litmus paper will onlyshow whether a substance is an acidor a base.***

• pH paper – paper that changes color based on the pH of the substance.

***pH paper shows the specific strength of the acid or base***

AcidsRed – Yellow (Light)

BasesYellow – Purple (Dark)

• Indicator – a substance that has a specific color for an acidic and basic substance.

Examples of an Indicators:

• Hydrangea – a flower that changes color based on the pH of the soil that the flowers grow in.

• Universal Indicator – a liquid that changes the color of the substance based on pH.

Neutralizing (Back to the Basics)Bronsted-Lowry Acids and Bases:Acids: Substances that give Hydrogen (H+)Base: Substances that accept Hydrogen (H+)

What happens when you add a base to an acid?

Answer: They become neutral and do not have the properties of either an acid or a base.

*An acid and a base mixture acts more like water*

Neutralizing: Acid + BaseThe idea of neutralization is used in labs all the time:

*If hydrochloric acid spills, the first thing to do is to pour baking soda (base) on the spill to make the hydrochloric acid not act like an acid anymore.

Neutral: In between an Acid and a Base

In between an Acid and Base is considered a neutral substance.

The most common neutral substance is Water.

Water is also considered amphoteric.

Amphoteric – something that can be a base and an acid.

Ex. Water (H2O) H-O-H H+ O-H-

pH, pOH, [H+], [OH-]

Titration (Solving for Concentration)

TitrationTitration: the process of mixing an acid and base to a

specific point to determine the concentration of the unknown acid or base.

Titration (Continued…)

Material needed for a Titration:Burette with Burette Clamp:Valve:

Allows for a very controlled, accurate, addition of the acid to base: Allows for support of the

burette clamp:

Equivalence Point: Balanced

• Equivalence Point: The point where the amount (moles) of acid equals the amount (moles) of base:

Moles Acid = Moles Base

Titration (Continued…)

Process for Titration:1) Start with unknown acid or base:

2) Add (2-3 drops) indicator: *Bromothymol Blue*

3) Add enough known acid or baseto change indicator:

Formula for determining the results of a titration:

• The formula for determining the molarity of an unknown acid or base:

MAVA = MBVB

A = AcidB = Base

• Neutral – a substance with the same amount of hydrogen ions and hydroxide ions.

• Neutralization – chemical reaction when an acid and base mix to form a salt and water

• Acid – donates hydrogen ions (protons)

• Base – donated hydroxide ions / accepts protons

• Acids and bases are so attracted to each other, that they have their own chemical reaction:

Neutralization Reaction: where an acid and a base react to form a salt and water.

Salt – an ionic bond with a metaland non-metal other than oxygen.

• Neutralization reactions are extremely reactive!

*Usually neutralization reactions are exothermic, or they release heat.

52.8˚C is about 127˚F

• We can predict the outcome of a neutralization reaction based on the chemical properties of an acid and a base.

Acid – Gives off protons (H+)

Base – Gives off hydroxide (OH-)

1) The protons will bond with the hydroxide ions to form water.

2) The cation (+) from the base will bond with the anion (-) from the acid to form the salt.

Determine the products for the following neutralization reactions:

HCl + NaOH +

H+ OH- H2O

H2O

Cl-Na+ NaCl

NaCl

Determine the products for the following neutralization reactions:

HF + LiOH +

H+ OH- H2O

H2O

F-Li+ LiF

LiF

Determine the products for the following neutralization reactions:

H2S + Ca(OH)2 +

2H+ 2OH- 2H2O

2H2O

S-2Ca+2 CaS

CaS

• Determine the products of the following neutralization reactions:

1) HF + NaOH +

2) HBr + KOH +

3) H3N + Al(OH)3 +

4) HNO3 + NH4OH +

H2O

H2O

3H2O

H2O

NaF

KBr

AlN

NH4NO3

- According to Bronsted-Lowry, acids gives off hydrogen ions (protons) and bases accept them.

*This means that a neutralization reaction is basically an exchange of a proton between the acid and the base*

Question: What’s keeping the base from give the hydrogen ion back to the acid?

Think of a conjugate base and acid as the result of the substance changing its mind:

Conjugate Acid – an base that has received a hydrogen ion (proton) and now wants to give the protons away.

Conjugate Base – an acid that has donated a hydrogen ion (proton) and how want to take the proton back.

When we clean a closet, we think of what we can put in the closet.

With the closet full, we wish we could have the empty, clean closet again.

An acid will always form a conjugate base.- an acid that gives a hydrogen will take on back.

A base will always form a conjugate acid.- a base that has a hydrogen will give it away.

- Determine the acid, base, conjugate acid (CA), and conjugate base (CB) in the following reaction.

HCl + OH- H2O + Cl-

HBr + NH3 Br- + NH4+

Acid Base Conjugate Base

Conjugate Acid

Acid Base Conjugate Base

Conjugate Acid

Determine the acid, base, conjugate acid (CA), conjugate base (CB) for the following reactions:

1) HF + OH- H2O + F-

2) H3PO4 + NH3 NH4+ + H2PO4

-

3) H2PO4- + NH3 HPO4

-2 + NH4+

4) H2S + OH- H2O + HS-

Acid Base CA CB

Acid Base CA CB

Acid Base CACB

Acid Base CA CB

- The strength of the acid or base can effect the properties of the substance.

pH = 0 - 4 *Completely Dissociates

Dissociates – splits into ion form (HCl H+ + Cl-)

Can conduct electricity well.

**More strength equals more movement of protons (+)

Examples: Lemon Juice, nitric acid, Sulfuric Acid.

pH = 4 – 6.99

Does not completely dissociate.

Weak acids are not strong enough to donate all their protons.

Does not conduct electricity well.

**Less strength equals less movement of protons (+)

Examples: Vinegar, Hydrogen Peroxide, Vitamin C.

pH = 11 - 14 *Completely Dissociates

Dissociates – splits into ion form (NaOH Na+ + OH-)

Can conduct electricity well.

**More strength equals more movement of hydroxide ions (OH-)

Examples: Lye, Drain Cleaner, Ammonia.

pH = 7.01 – 11

Does not completely dissociate.

Weak bases are not strong enough to donate all their hydroxide ions.

Does not conduct electricity well.

**Less strength equals less movement of hydroxide ions.(OH-)

Examples: Baking Soda, Seawater, Toothpaste.

So how do we measure the strength of an acid or base in terms of dissociation?

KA = Acid dissociation constant.

***KA illustrates the ability for an acid to dissociate and release hydrogen ions (H+).***

In basic terms, KA measure the ratio of products

(protons) base on the amount of reactants.

KA = [ Products] [Reactants]

• Strong Acids have a KA higher than one. • Weak Acids have a KA lower than one. • Acids with a high KA can dissociate completely

which means a higher movement of protons which means a higher conductivity of electricity.

Lemons have a very strong Kaand because it is such a strong acid, it canprovide an electrical charge through thelemon.

***The battery is giving off .902 volts of electricity which is very similar to a battery that gives of about 1.5 volts of electrical charge.

KB = dissociation constant for bases

***KB illustrates the ability for an base to dissociate and release hydroxide ions (OH-).***

KB = [ Products] [Reactants] Strong bases have a KB higher than one. Weak bases have a KB lower than one.

Nitric Acid (HNO3) Phosphoric Acid (H3PO4)

Mono – “one” or “singular”

Protic – proton or hydrogen ion (H+)

Monoprotic Acid - an acid consisting of one proton.

Examples: Hydrochloric Acid Hydrofluoric Acid

(HCl) (HF)

Poly – “more than one” or “many”

Protic – proton or hydrogen ion (H+)

Polyprotic Acid - an acid consisting of two or more protons.

Examples: Carbonic Acid Sulfuric Acid (H2CO3) (H2SO4)

Monoprotic Acids Polyprotic Acids

- Only have one proton - Has more than one protons

- Tend to be weaker - Tend to be stronger

Examples: HCl, HI, HF Example: H2S, H2CO3, H3PO4

- Has only 1 pK point. - Has more than one pK point.

pK point – a point where the pH of the substance will increase rapidly.

What is a pK point?

A pK point is where the substance hits it equivalence point and has a drastic change in pH.

*This will happen for each proton in the acid.*

How can we tell the difference between a monoprotic and polyprotic acid?

Polyprotic Acid

Determine if the following acids are monoprotic or polyprotic:

1) Hydrochloric Acid (HCl)

2) Sulfurous Acid (H2SO3)

3) Perchloric Acid (HClO4)

4) Cyanic Acid (HCNO)

5) Oxalic Acid (H2C2O4)

Monoprotic Acid

Polyprotic Acid

Monoprotic Acid

Monoprotic Acid

Polyprotic Acid

Is the titration curve below, a monoprotic or polyprotic acid? Explain how you know.

Answer:This is a polyprotic acid. The reason why is it has two equivalence points or two jumps in the graph.