Acids and Bases

The basics…• Acids and bases are a group of compounds

that share similar chemical properties. • There are a few ways that this group can be

classified.

Lewis Acids and Bases

Brønsted-Lowry Acid and Bases

Arrhenius Acid and Bases

Arrhenius Acids and Bases

• Arrhenius’ is the most common definition of acidic and basic compounds.

• Acid: Releases an H+ (hydronium) ion in solution– HA H+ + A-

• Base: Releases an OH- (hydroxide) ion in solution– BOH B+ + OH-

or H3O+

Common Arrhenius Acids and Bases

HCl H+ + Cl-

Ca(OH)2 Ca2+ + 2OH-

Regents Question

H-

H+

H3O+

OH-

BOH B+ + OH-

An Arrhenius Acid will produce which positively charged ion in solution?

1. Hydronium ion2. Hydride ion3. Hydroxide ion4. Hydrogen

In the following neutralization reaction, which compound is considered an

Arrhenius base? HCl + NaOH H2O + NaCl

1. HCl2. NaOH3. H2O

4. NaCl

Brønsted-Lowry Model

• While Arrhenius was H+ and OH-, Brønsted-Lowry focused exclusively on the H+.

• Brønsted-Lowry Acid: Donates an H+ ion• Brønsted-Lowry Base: Accepts an H+ ion

HCl + NH3 NH4+ + Cl-

Donates H+

Accepts H+

Who is the Brønsted-Lowry Base?HF + H2O H3O+ + F-

1.HF2.H2O

3.H3O+

4.F-

Who is the Brønsted-Lowry Acid?H3O+ + Cl- H2O + HCl

1.HCl2.H2O

3.H3O+

4.Cl-

Lewis’ Model: Acids and Bases• Lewis’ Model further expands the definition of

acids and bases• Lewis Acid: Electron-Pair Acceptor• Lewis Base: Electron-Pair Donor

LewisAcid

LewisBase

Accepts Electrons

DonatesElectrons

Strengths of Acids and Bases

• Ionize: To break apart into ions in solution• A strong acid/base will break apart completely • A weak acid/base will produce fewer ions

HCl H+ + Cl-

HF HF + H+ + F-

CompletelyIonizes

PartiallyIonizes

pH Scale• We measure the strength of Arrhenius acids

using the pH scale.

Neutral

BaseAcid

pH Scale• pH measures the concentration of H+ ions in solution• An increase of 1 pH means a 10 times increase in OH-

(or a 10 time decrease in H+)• At a pH of 7 (neutral) there are equal amounts of H+

and OH- in solution. • Acids have more H+ in solution• Bases have less H+ in solution

Which of the following compounds is an Arrhenius Acid?

1.NaOH2.NH3

3.CaCl2

4.H2SO4

In the following equation, which compound is the Brønsted-Lowry base?

HCl + H2O H3O+ + Cl-

1.Cl-

2.H3O+

3.H2O

4.HCl

Measures of Concentration

Concentration

• The amount of a solute in a solvent is something that we can quantify (assign a number to).

• We measure this in terms of molarity:

SolutionofLiters

SoluteofMolesMolarity

__

__

Moles

• Remember we can always determine moles from a given mass using the formula:

Calculating Molarity

• Consider the following statement: In a 500L solution, 50 moles of NaCl are dissolved.

Calculating Molarity

• Consider the following statement: 30 moles of KCl are disssolved in 60 L solution.

Significant Figures

http://blog.swivel.com/weblog/2007/02/ode_to_numbers.html

Not All Numbers Were Created Equal

When we are measuring an

object, we always guess a little

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Guessing

2 . 4 5Definite

Definite

Guess

Remember, you can only guess

on one number.

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Sig Figs Rules

• When adding or subtracting measurements, your answer can have no more decimal places than the measurement with the fewest decimal places. 45.6

54.65324.93425.18425.2

+

Sig Figs Rules

• When multiplying or dividing measurements, your answer can have no more numbers than the fewest number of significant (definite) figures. 48.3

296.6100

1 Sig Fig

The Rules of Zero

Atlantic

Right

Pacific

Left

The Rules of Zero

AtlanticAbsentRight

PacificPresentLeft

How many significant figures?

1.0450

Determine if there is a decimal present or absent.

The Rules of Zero

Atlantic

Right

Pacific

Left

How many significant figures?

Start counting with the first non-zero number.

1.0450

The Rules of Zero

AtlanticAbsentRight

PacificPresentLeft 1.0450

How many significant figures?

5 Sig Figs

The Rules of Zero

AtlanticAbsentRight

PacificPresentLeft 98700

How many significant figures?

3 Sig Figs

The Rules of Zero

AtlanticAbsentRight

PacificPresentLeft 98.70

How many significant figures?

4 Sig Figs

Acid-Base Titrations

Classic Part II Question

What we know…

• An Arrhenius acid is one that produces H+ or H3O+ in solution.

• When an acid reacts with a base, a neutralization reaction occurs.

• A neutralization reaction produces a salt and water each and every time.

Neutralization Reactions

• In a neutralization reaction, acid reacts with base to produce salt and water.

• Neutralization reactions are a type of double replacement reaction

HCl + Ca(OH)2 H2O + CaCl2

Acid Base Water Salt

Titration reaction

• Titration reactions are used to determine the concentration of an unknown acid.

MAVA = MBVB

Moles H+ = Moles OH-

• We can calculate the amount needed to neutralize any solution.

Titration• How many milliliters of 3M NaOH are needed

to neutralize 400mL of 2M HCl?

How much 4M NaOH is needed to neutralize 50mL of 2M HCl?

How much 6M HCl are needed to neutralize 100mL of 3M NaOH?

Titrating an Unknown Solution

• If we combine the information we have about titrations and indicators, we can determine the concentration of an unknown solution.

• We will need to use an indicator that has a changing point that is close to the neutral point.

Titration

Acid of Unknown

Concentration

Base

When the indicator changes color, all of the H+ has been neutralized.

If we know the VA, the MB and VB of the system we can back calculate the concentration of the acid.

VA

VB

MB

Titration• What is the concentration of 50mL of an acid

that is titrated to neutrality with 75mL of 3M NaOH?

Titration• What is the concentration of 80mL of a base

that is titrated to neutrality with 40mL of 2M HCl?

A student neutralized 16.4 milliliters of HCl by adding 12.7 milliliters of 0.0620 M KOH. What was the molarity of the

HCl acid?