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Announcements & Agenda (02/26/07). You should be reading Ch 10! Quiz on Friday! Bring resource CD to lab! Today Acid & base reactions (8.6) Conjugate acids & bases (8.2), buffers (8.7) Introduction to Organic Chemistry (Ch 10).

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announcements agenda 02 26 07
Announcements& Agenda(02/26/07)
  • You should be reading Ch 10!
  • Quiz on Friday!
  • Bring resource CD to lab!
  • Today
    • Acid & base reactions (8.6)
    • Conjugate acids & bases (8.2), buffers (8.7)
    • Introduction to Organic Chemistry (Ch 10)
last time ionization of water a basis for understanding ph h concentrations
Last Time: Ionization of Water: A Basis for Understanding pH (H+ concentrations)

In water occasionally,

  • H+ is transferred from 1 H2O molecule to another.
  • one water acts an acid, the another acts as a base.

H2O + H2O H3O++ OH−

.. .. .. ..

:O: H + H:O: H:O:H+ + :O:H−

.. .. .. ..

HH H

water water hydronium hydroxide ion (+)ion (-)

last time h 3 o and oh in solutions
Last Time: [H3O+] and [OH−] in Solutions

IMPORTANT: Kw is always 1.0 x 10−14.

slide4

Last Time: pH as a Measure of A/B Strength

pH = - log [H3O+]

NOTE: pH is a logarithmic scale!!!

slide5
If an area received 1 inch of rain with a pH of 4, how much more neutral rain (pH 7) would be needed to have a final pH of 6?
  • Approximately 2 inches
  • Approximately 9 inches
  • Approximately 20 inches
  • Approximately 100 inches
calculating h 3 o from ph
Calculating [H3O+] from pH

The [H3O+] can be expressed by using the pH as the negative power of 10.

[H3O+] = 1 x 10 -pH

For pH = 3.0, the [H3O+] = 1 x 10 -3

On a calculator

1. Enter the pH value 3.0

2. Change sign -3.0

3. Use the inverse log key (or 10x) to obtain

the [H30+]. = 1 x 10 -3 M

neutralization rxns of acids bases
Neutralization Rxns of Acids & Bases

In a neutralization reaction:

  • a base such as NaOH reacts with an acid such as HCl.

HCl + H2O H3O+ + Cl−

NaOH Na+ + OH−

  • the H3O+ from the acid and the OH− from the base form water.

H3O+ + OH− 2 H2O

bases used in some antacids
Bases Used in Some Antacids

Antacids are used to neutralize stomach acid (HCl).

neutralization equations
Neutralization Equations

In the equation for neutralization, an acid and a base produce a salt and water.

acid base saltwater

HCl + NaOH NaCl + H2O

2HCl + Ca(OH)2 CaCl2 + 2H2O

Balance these like any other reaction!

solving problems
Solving Problems…

What is the molarity of an HCl solution if 18.5 mL of a 0.225 M NaOH are required to neutralize 10.0 mL HCl?

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

Method:

Get into moles with “known”:

Given: 18.5 mL of 0.225 M NaOH

Do a moles-to-moles conversion

Get out of moles with “unknown”:

slide12

18.5 mL NaOH x 1 L NaOHx 0.225 mole NaOH

1000 mL NaOH 1 L NaOH

x 1 mole HCl = 0.00416 mole HCl

1 mole NaOH

MHCl= 0.00416 mole HCl = 0.416 M HCl

0.0100 L HCl

Key Point: In a neutralization reaction, the # of OH- moles MUST EQUAL the # of H+ moles!!!

two more acid base reactions
Two More Acid/Base Reactions…

1. Acids react with metals

  • such as K, Na, Ca, Mg, Al, Zn, Fe, and Sn.
  • to produce hydrogen gas and the salt of the metal.

Molecular equations:

2K(s) + 2HCl(aq) 2KCl(aq) + H2(g)

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

acids and carbonates
Acids and Carbonates

Acids react

  • with carbonates & hydrogen carbonates
  • to produce carbon dioxide gas, a salt, & water.

2HCl(aq) + CaCO3(s) CO2(g) + CaCl2(aq) + H2O(l)

HCl(aq) + NaHCO3(s) CO2(g) + NaCl (aq) + H2O(l)

conjugate acid base pairs
Conjugate Acid-Base Pairs

For ALL acid base reactions, there are 2 conjugate acid-base pairs.

  • Each pair is related by the loss and gain of H+ .
  • One pair occurs in the forward direction.
  • One pair occurs in the reverse direction.

conjugate acid-base pair 1

HA + B A− + BH+

conjugate acid-base pair 2

example reaction of hf and h 2 o
Example: Reaction of HF and H2O
  • one conjugate acid-base pair is HF/F−.
  • the other conjugate acid-base pair is H2O/H3O+.
  • each pair is related by a loss and gain of H+.
learning check
Learning Check

A. Write the conjugate base of the following.

1. HBr

2. H2S

3. H2CO3

B. Write the conjugate acid of the following.

1. NO2-

2. NH3

3. OH-

buffers
Buffers

When an acid or base is added

  • to pure water, the pH changes drastically.
  • to a buffer solution, the pH is maintained; pH does not change.
buffers what are they
Buffers: What are they?
  • resist changes in pH when an acid/base is added
  • in the body, absorb H3O+ or OH- from foods and cellular processes to maintain pH.
  • are important in the proper functioning of cells and blood.
  • in blood maintain a pH close to 7.4. A change in the pH of the blood affects the uptake of oxygen and cellular processes.
components of a buffer
Components of a Buffer
  • contains a combination of acid-base conjugate pairs.
  • may contain a weak acid and a salt of its conjugate base.
  • typically has equal concentrations of a weak acid and its salt.
  • may also contain a weak base and a salt of the conjugate acid.
buffer action
Buffer Action

In the acetic acid/acetate buffer with acetic acid

(CH3COOH) and sodium acetate (CH3COONa)

  • The salt produces acetate ions and sodium ions.

CH3COONa(aq) CH3COO-(aq) + Na+ (aq)

  • The salt is added to provide a higher concentration of the conjugate base CH3COO- than the weak acid alone.

CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)

Large amount Large amount

function of the weak acid in a buffer
Function of the Weak Acid in a Buffer

The function of the weak acid in a buffer is to neutralize a base. The acetate ion produced adds to the available acetate.

CH3COOH + OH− CH3COO− + H2O

acetic acidbase acetate ion water

function of the conjugate base
Function of the Conjugate Base

The function of the acetate ion CH3COO− is to neutralize H3O+ from acids. The acetic acid produced contributes to the available weak acid.

CH3COO− + H3O+ CH3COOH + H2O

acetate ion acid acetic acidwater

summary of buffer action
Summary of Buffer Action

Buffer action occurs as

  • the weak acid in a buffer neutralizes base.
  • the conjugate base in the buffer neutralizes acid.
  • the pH of the solution is maintained.
organic chemistry
Organic Chemistry

An organic compound

  • is a compound made from carbon atoms.
  • has one or more C atoms.
  • has many H atoms.
  • may also contain O, S, N, and halogens.
organic compounds
Organic Compounds

Typical organic compounds

  • have covalent bonds.
  • have low melting points.
  • have low boiling points.
  • are flammable.
  • are soluble in nonpolar solvents.
  • are usually not soluble in water.

oil (organic) and water (inorganic)

organic vs inorganic
Organic vs. Inorganic
  • Propane, C3H8, is an organic compound used as a fuel.
  • NaCl, salt, is an inorganic compound composed of Na+ and Cl- ions.
writing formulas for alkanes
Writing Formulas for Alkanes

In organic compounds

  • carbon has 4 valence electrons and hydrogen has 1.

• C • H •

  • to achieve an octet, C forms four bonds.

H H

 

H  C  H H C H

 

H H CH4 , methane

tetrahedral structure of carbon
Tetrahedral Structure of Carbon

VSEPR theory predicts that a carbon atom with four single, covalent bonds, has a tetrahedral shape.

tetrahedral structure of carbon32
Tetrahedral Structure of Carbon

In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape.

names of alkanes
Names of Alkanes

The names of alkanes

  • are determined by the IUPAC (International Union of Pure and Applied Chemistry) system.
  • end in –ane.
  • with 1-4 carbons in a chain use prefixes as follows.

Name # Carbons Structural Formula

Methane 1 CH4

Ethane 2 CH3CH3

Propane 3 CH3CH2CH3

Butane 4 CH3CH2CH2CH3

names of alkanes35
Names of Alkanes

Alkanes with 5-10 carbon atoms in a chain use Greek prefixes.

Name # Carbons Structural Formula

Pentane 5 CH3CH2CH2CH2CH3

Hexane 6 CH3CH2CH2CH2CH2CH3

Heptane 7 CH3CH2CH2CH2CH2CH2CH3

Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3

Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3

Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

getting ziggy with it
Getting ziggy with it.

Hexane

  • is an alkane with six carbon atoms in a continuous chain.
  • has a “zig-zag” look because each carbon atom is at the center of a tetrahedron.
  • is represented by a ball-and-stick model as shown below.
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