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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 l.jpg
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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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 (-)


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Last Time: [H (H3O+] and [OH−] in Solutions

IMPORTANT: Kw is always 1.0 x 10−14.


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

pH = - log [H3O+]

NOTE: pH is a logarithmic scale!!!


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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


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[H more neutral rain (pH 7) would be needed to have a final pH of 6?3O+], [OH-], and pH Values


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Calculating [H more neutral rain (pH 7) would be needed to have a final pH of 6?3O+] 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


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Neutralization Rxns of Acids & Bases more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Bases Used in Some Antacids more neutral rain (pH 7) would be needed to have a final pH of 6?

Antacids are used to neutralize stomach acid (HCl).


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Neutralization Equations more neutral rain (pH 7) would be needed to have a final pH of 6?

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!


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Solving Problems… more neutral rain (pH 7) would be needed to have a final pH of 6?

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”:


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18.5 mL NaOH x more neutral rain (pH 7) would be needed to have a final pH of 6? 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!!!


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Two More Acid/Base Reactions… more neutral rain (pH 7) would be needed to have a final pH of 6?

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)


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Acids and Carbonates more neutral rain (pH 7) would be needed to have a final pH of 6?

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)


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Conjugate Acid-Base Pairs more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Example: Reaction of HF and H more neutral rain (pH 7) would be needed to have a final pH of 6?2O

  • 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+.


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Learning Check more neutral rain (pH 7) would be needed to have a final pH of 6?

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-


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Buffers more neutral rain (pH 7) would be needed to have a final pH of 6?

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.


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Buffers: What are they? more neutral rain (pH 7) would be needed to have a final pH of 6?

  • 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.


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Components of a Buffer more neutral rain (pH 7) would be needed to have a final pH of 6?

  • 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.


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Buffer Action more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Function of the Weak Acid in a Buffer more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Function of the Conjugate Base more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Summary of Buffer Action more neutral rain (pH 7) would be needed to have a final pH of 6?

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.


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Chapter 10: Introduction to more neutral rain (pH 7) would be needed to have a final pH of 6?Organic Chemistry - Alkanes


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Organic Chemistry more neutral rain (pH 7) would be needed to have a final pH of 6?

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.


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Organic Compounds more neutral rain (pH 7) would be needed to have a final pH of 6?

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)


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Organic vs. Inorganic more neutral rain (pH 7) would be needed to have a final pH of 6?

  • Propane, C3H8, is an organic compound used as a fuel.

  • NaCl, salt, is an inorganic compound composed of Na+ and Cl- ions.


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Comparing Organic and Inorganic Compounds more neutral rain (pH 7) would be needed to have a final pH of 6?


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Writing Formulas for Alkanes more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Tetrahedral Structure of Carbon more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Tetrahedral Structure of Carbon more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Structural Formulas: Expanded & Condensed Structures more neutral rain (pH 7) would be needed to have a final pH of 6?


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Names of Alkanes more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Names of Alkanes more neutral rain (pH 7) would be needed to have a final pH of 6?

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


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Getting ziggy with it. more neutral rain (pH 7) would be needed to have a final pH of 6?

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.