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) Acid & base reactions (8.6) Conjugate acids & bases (8.2), buffers (8.7) Conjugate acids & bases (8.2), buffers (8.7) Introduction to Organic Chemistry (Ch 10) Introduction to Organic Chemistry (Ch 10)

2 In water occasionally, H + is transferred from 1 H 2 O molecule to another.H + is transferred from 1 H 2 O molecule to another. one water acts an acid, the another acts as a base.one water acts an acid, the another acts as a base. H 2 O + H 2 O H 3 O + + OH − :O: H + H:O: H:O:H + + :O:H − :O: H + H:O: H:O:H + + :O:H − H H H H H H water water hydronium hydroxide ion (+) ion (-) water water hydronium hydroxide ion (+) ion (-) Last Time: Ionization of Water: A Basis for Understanding pH (H + concentrations)

3 Last Time: [H 3 O + ] and [OH − ] in Solutions IMPORTANT: K w is always 1.0 x 10 −14.

4 Last Time: pH as a Measure of A/B Strength NOTE: pH is a logarithmic scale!!! pH = - log [H 3 O + ]

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? 1.Approximately 2 inches 2.Approximately 9 inches 3.Approximately 20 inches 4.Approximately 100 inches 12345

6 [H 3 O + ], [OH - ], and pH Values

7 Calculating [H 3 O + ] from pH The [H 3 O + ] can be expressed by using the pH as the negative power of 10. [H 3 O + ] = 1 x 10 -pH For pH = 3.0, the [H 3 O + ] = 1 x On a calculator 1. Enter the pH value Change sign Use the inverse log key (or 10 x ) to obtain the [H ]. = 1 x M the [H ]. = 1 x M

8 In a neutralization reaction: a base such as NaOH reacts with an acid such as HCl.a base such as NaOH reacts with an acid such as HCl. HCl + H 2 OH 3 O + + Cl − NaOHNa + + OH − the H 3 O + from the acid and the OH − from the base form water.the H 3 O + from the acid and the OH − from the base form water. H 3 O + + OH − 2 H 2 O H 3 O + + OH − 2 H 2 O Neutralization Rxns of Acids & Bases

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

10 In the equation for neutralization, an acid and a base produce a salt and water. acid base salt water acid base salt water HCl + NaOH NaCl + H 2 O HCl + NaOH NaCl + H 2 O 2HCl + Ca(OH) 2 CaCl 2 + 2H 2 O 2HCl + Ca(OH) 2 CaCl 2 + 2H 2 O Neutralization Equations Balance these like any other reaction!

11 Solving Problems… What is the molarity of an HCl solution if 18.5 mL of a M NaOH are required to neutralize 10.0 mL HCl? HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)Method: Get into moles with “known”: Given: 18.5 mL of M NaOH Do a moles-to-moles conversion Get out of moles with “unknown”:

mL NaOH x 1 L NaOH x mole NaOH 1000 mL NaOH 1 L NaOH 1000 mL NaOH 1 L NaOH x 1 mole HCl = mole HCl x 1 mole HCl = mole HCl 1 mole NaOH 1 mole NaOH M HCl = mole HCl = M HCl L HCl 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.such as K, Na, Ca, Mg, Al, Zn, Fe, and Sn. to produce hydrogen gas and the salt of the metal.to produce hydrogen gas and the salt of the metal. Molecular equations: 2K(s) + 2HCl(aq) 2KCl(aq) + H 2 (g) Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g)

14 Acids and Carbonates Acids react with carbonates & hydrogen carbonateswith carbonates & hydrogen carbonates to produce carbon dioxide gas, a salt, & water.to produce carbon dioxide gas, a salt, & water. 2HCl(aq) + CaCO 3 (s) CO 2 (g) + CaCl 2 (aq) + H 2 O(l) HCl(aq) + NaHCO 3 (s) CO 2 (g) + NaCl (aq) + H 2 O(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 +. Each pair is related by the loss and gain of H +. One pair occurs in the forward direction. One pair occurs in the forward direction. One pair occurs in the reverse direction. One pair occurs in the reverse direction. conjugate acid-base pair 1 conjugate acid-base pair 1 HA + B A − + BH + HA + B A − + BH + conjugate acid-base pair 2

16 Example: Reaction of HF and H 2 O one conjugate acid-base pair is HF/F −.one conjugate acid-base pair is HF/F −. the other conjugate acid-base pair is H 2 O/H 3 O +.the other conjugate acid-base pair is H 2 O/H 3 O +. each pair is related by a loss and gain of H +.each pair is related by a loss and gain of H +.

17 Learning Check A. Write the conjugate base of the following. 1. HBr 1. HBr 2. H 2 S 2. H 2 S 3. H 2 CO 3 3. H 2 CO 3 B. Write the conjugate acid of the following. 1. NO NO NH 3 2. NH 3 3. OH - 3. OH -

18 Buffers When an acid or base is added to pure water, the pH changes drastically.to pure water, the pH changes drastically. to a buffer solution, the pH is maintained; pH does not change.to a buffer solution, the pH is maintained; pH does not change.

19 resist changes in pH when an acid/base is addedresist changes in pH when an acid/base is added in the body, absorb H 3 O + or OH - from foods and cellular processes to maintain pH.in the body, absorb H 3 O + or OH - from foods and cellular processes to maintain pH. are important in the proper functioning of cells and blood.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.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. Buffers: What are they?

20 contains a combination of acid-base conjugate pairs.contains a combination of acid-base conjugate pairs. may contain a weak acid and a salt of its conjugate base.may contain a weak acid and a salt of its conjugate base. typically has equal concentrations of a weak acid and its salt.typically has equal concentrations of a weak acid and its salt. may also contain a weak base and a salt of the conjugate acid.may also contain a weak base and a salt of the conjugate acid. Components of a Buffer

21 In the acetic acid/acetate buffer with acetic acid (CH 3 COOH) and sodium acetate (CH 3 COONa) The salt produces acetate ions and sodium ions.The salt produces acetate ions and sodium ions. CH 3 COONa(aq) CH 3 COO - (aq) + Na + (aq) The salt is added to provide a higher concentration of the conjugate base CH 3 COO - than the weak acid alone.The salt is added to provide a higher concentration of the conjugate base CH 3 COO - than the weak acid alone. CH 3 COOH(aq) + H 2 O(l) CH 3 COO - (aq) + H 3 O + (aq) Large amount Large amount Large amount Large amount Buffer Action

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. CH 3 COOH + OH − CH 3 COO − + H 2 O CH 3 COOH + OH − CH 3 COO − + H 2 O acetic acid base acetate ion water acetic acid base acetate ion water

23 Function of the Conjugate Base The function of the acetate ion CH 3 COO − is to neutralize H 3 O + from acids. The acetic acid produced contributes to the available weak acid. CH 3 COO − + H 3 O + CH 3 COOH + H 2 O CH 3 COO − + H 3 O + CH 3 COOH + H 2 O acetate ion acid acetic acid water acetate ion acid acetic acid water

24 Summary of Buffer Action Buffer action occurs as the weak acid in a buffer neutralizes base.the weak acid in a buffer neutralizes base. the conjugate base in the buffer neutralizes acid.the conjugate base in the buffer neutralizes acid. the pH of the solution is maintained.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.is a compound made from carbon atoms. has one or more C atoms.has one or more C atoms. has many H atoms.has many H atoms. may also contain O, S, N, and halogens.may also contain O, S, N, and halogens.

27 Organic Compounds Typical organic compounds have covalent bonds.have covalent bonds. have low melting points.have low melting points. have low boiling points.have low boiling points. are flammable.are flammable. are soluble in nonpolar solvents.are soluble in nonpolar solvents. are usually not soluble in water.are usually not soluble in water. oil (organic) and water (inorganic)

28 Organic vs. Inorganic Propane, C 3 H 8, is an organic compound used as a fuel.Propane, C 3 H 8, is an organic compound used as a fuel. NaCl, salt, is an inorganic compound composed of Na + and Cl - ions.NaCl, salt, is an inorganic compound composed of Na + and Cl - ions.

29 Comparing Organic and Inorganic Compounds

30 In organic compounds carbon has 4 valence electrons and hydrogen has 1.carbon has 4 valence electrons and hydrogen has 1. C H C H to achieve an octet, C forms four bonds.to achieve an octet, C forms four bonds. H H H H     H  C  H H C H     H H CH 4, methane H H CH 4, methane Writing Formulas for Alkanes

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.are determined by the IUPAC (International Union of Pure and Applied Chemistry) system. end in –ane.end in –ane. with 1-4 carbons in a chain use prefixes as follows.with 1-4 carbons in a chain use prefixes as follows. Name # Carbons Structural Formula Methane1CH 4 Ethane2CH 3 CH 3 Propane3CH 3 CH 2 CH 3 Butane4CH 3 CH 2 CH 2 CH 3

35 Names of Alkanes Alkanes with 5-10 carbon atoms in a chain use Greek prefixes. Name # Carbons Structural Formula Pentane 5 CH 3 CH 2 CH 2 CH 2 CH 3 Hexane 6 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Heptane 7 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Octane 8 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Nonane 9 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Decane 10 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3

36 Getting ziggy with it. Hexane is an alkane with six carbon atoms in a continuous chain.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.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.is represented by a ball-and-stick model as shown below.