Announcements & Agenda (02/26/07)

1. 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)

2. 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 (-)

3. Last Time: [H3O+] and [OH−] in Solutions IMPORTANT: Kw is always 1.0 x 10−14.

4. Last Time: pH as a Measure of A/B Strength pH = - log [H3O+] NOTE: pH is a logarithmic scale!!!

5. 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

6. [H3O+], [OH-], and pH Values

7. 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

8. 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

9. Bases Used in Some Antacids Antacids are used to neutralize stomach acid (HCl).

10. 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!

11. 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”:

12. 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!!!

13. 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)

14. 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)

15. 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

16. 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+.

17. 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-

18. 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.

19. 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.

20. 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.

21. 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

22. 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

23. 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

24. 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.

25. Chapter 10: Introduction to Organic Chemistry - Alkanes

26. 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.

27. 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)

28. 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.

29. Comparing Organic and Inorganic Compounds

30. 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

31. Tetrahedral Structure of Carbon VSEPR theory predicts that a carbon atom with four single, covalent bonds, has a tetrahedral shape.

32. Tetrahedral Structure of Carbon In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape.

33. Structural Formulas: Expanded & Condensed Structures

34. 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

35. 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

36. 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.