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chem 101 chapter 6 slides

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Published on January 4, 2008

Author: Me_I

Source: authorstream.com

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Implications of H-bonding in Water:  Implications of H-bonding in Water Water can dissolve a wide range of solutes by forming hydrogen bonds with them. Your DNA is held together by hydrogen bonds:  Your DNA is held together by hydrogen bonds + - + - + - + - + - Ionic Bonding:  Ionic Bonding Ionic bonds are created between 2 atoms with very different electronegativities (EN). Na Cl Group 1a: Very low EN. Will get full octet if it gives away 1 electron (e-) Group 7a: Very high EN. Will get full octet if it gets 1 electron (e-) Formulas and names of simple ionic compounds:  Formulas and names of simple ionic compounds Combine cations and anions in such a way as to neutralize the charge MgCl2 Name of simple ionic compounds = name of cation + name of anion with –ide instead of –ine Magnesium Chloride What compounds would be made out of: Na and Br? Ca and F? Formulas and names of polyatomic ionic compounds:  Formulas and names of polyatomic ionic compounds Combine cations and anions in such a way as to neutralize the charge NH4Cl; Ca3(PO4)2 Name of polyatomic ionic compounds = name of cation + name of anion Ammonium Chloride; Calcium Phosphate What compounds would be made out of: K+ and SO32-? NH4+ and PO43- ? What does it mean for something to be dissolved in something else?:  What does it mean for something to be dissolved in something else? Key is the presence of intermolecular forces between the solvent and the solute Salt (NaCl) Glucose Electrolytes vs. non-electrolytes:  Electrolytes vs. non-electrolytes Pure distilled water (non-conducting) Sugar dissolved in water (non-conducting): a nonelectrolyte NaCl dissolved in water (conducting): an electrolyte Electrolytes are salts:  Electrolytes are salts Salts are compounds that are held together by ionic bonds When some salts are combined with water, these ionic bonds break and the charges. are separated. Electrolytes conduct electricity:  Electrolytes conduct electricity Nonelectrolytes are covalent compounds :  Nonelectrolytes are covalent compounds Glucose in water Hydrogen Bond Chapter 6: Neutralizing the threat of acid rain:  Chapter 6: Neutralizing the threat of acid rain What is an acid? What is a base? How do we express how acidic or basic something is? How do acids and bases react? What is acid rain? Where does it come from? What are the effects of acid rain? Definitions of acids and bases:  Definitions of acids and bases Acid: Generates H+ ions HCl  H+ + Cl- HNO3  H+ + NO3- EOC Problem 33: CH3COOH Also called “protons.” Why?? Definitions of acids and bases:  Definitions of acids and bases Acid: Generates H+ ions HCl  H+ + Cl- HNO3  H+ + NO3- HCl + H2O  H3O+ + Cl- HNO3 + H2O  H3O+ + NO3- H+ ions don’t generally exist by themselves. Instead, they combine with water. H+ + H2O  H3O+ Hydronium ion Still an ok “shorthand” to use in many cases. Definitions of acids and bases:  Definitions of acids and bases Base: Generates OH- ions NaOH  Na+ + OH- Ca(OH)2  Ca2+ + 2 OH- But Ammonia (NH3) is a base! Generates OH- when it reacts with water NH3 + H2O  NH4+ + OH- Where is the charge? O or H? How do we express how acidic something is?:  How do we express how acidic something is? HCl  H+ + Cl- We have defined acidity as being directly related to H+ ions. How might we quantify this idea? Molarity of H+, or [H+] Quantifying acidity:  Quantifying acidity [H+] in pure water = 0.0000001 M [H+] in acid rain = 0.0001 M Is this a convenient way of quantifying acidity? [H+] in pure water = 1 x 10-7 M [H+] in acid rain = 1 x 10-4 M Better, but. . . Why don’t we just use this #? Quantifying acidity:  Quantifying acidity [H+] in pure water = 0.0000001 M [H+] in acid rain = 0.0001 M Is this a convenient way of quantifying acidity? [H+] in pure water = 1 x 10-7 M [H+] in acid rain = 1 x 10-4 M Better, but. . . Why don’t we just use this #? Using pH:  Using pH [H+] in Coke = 0.0016 M pH = -log (0.0016) = -log (1.6 x 10-3) = 2.8 A solution is made in which 50 mg HCl(g) is dissolved in enough water to make a 100 mL solution. Assuming all the HCl dissociates into H+ and Cl- in water, what is the pH of this solution? Using pH:  Using pH [H+] in Coke = 0.0016 M pH = -log (0.0016) = -log (1.6 x 10-3) = 2.8 A solution is made in which 50 mg HCl(g) is dissolved in enough water to make a 100 mL solution. Assuming all the HCl dissociates into H+ and Cl- in water, what is the pH of this solution? Quantifying acidity:  Quantifying acidity [H+] in pure water = 0.0000001 M [H+] in acid rain = 0.0001 M Is this a convenient way of quantifying acidity? pH:  pH pH = “power of Hydrogen” Uses a logarithmic scale (powers of 10 – good for expressing numbers in a broad range) Using pH:  Using pH [H+] in Coke = 0.0016 M pH = -log (0.0016) = -log (1.6 x 10-3) = 2.8 A solution is made in which 50 mg HCl(g) is dissolved in enough water to make a 100 mL solution. Assuming all the HCl dissociates into H+ and Cl- in water, what is the pH of this solution? Dissociation of water:  Dissociation of water Pure water H OH H OH H OH H OH H OH H+ H+ OH- OH- If this solution were acidic, how should we change this drawing? What if it were basic? Acids and bases in water:  Acids and bases in water How do acids and bases react?:  How do acids and bases react? HCl + NaOH  HBr + KOH  HNO3 + NaOH  Ca(OH)2 + HCl  On your own: Slide26:  6.5 Why is rain naturally acidic? Carbon dioxide in the atmosphere dissolves to a slight extent in water and reacts with it to produce a slightly acidic solution of carbonic acid: CO2(g) + H2O(l) H2CO3 (aq) H2CO3 (aq) H+(aq)  + HCO3-(aq) The carbonic acid dissociates slightly, leading to rain with a pH around 5.3. What makes acid rain acidic?:  What makes acid rain acidic? Scientists analyzed the composition of acid rain and found: NO2 NO SO2 SO3 No H+ to donate! How can these be acids? NOx SOx How can NOx and SOx be acidic?:  How can NOx and SOx be acidic? Recall: CO2(g) + H2O(l) H2CO3 (aq) H2CO3 (aq) H+(aq)  + HCO3-(aq) Now consider SO4 and SO3. Can you write products for the following reactions? SO4 + H2O  SO3 + H2O  How can NOx and SOx be acidic?:  How can NOx and SOx be acidic? Recall: CO2(g) + H2O(l) H2CO3 (aq) H2CO3 (aq) H+(aq)  + HCO3-(aq) Now consider SO4 and SO3. Can you write products for the following reactions? SO4 + H2O  SO3 + H2O  Slide30:  6.8 4 NO2(g) + 2 H2O(l) + O2(g) 4 HNO3(aq) Like sulfuric acid, nitric acid also dissociates to release the H+ ion: HNO3 (aq) H+(aq) + NO3-(aq) What about NOx? What can be done??:  What can be done?? Think of the sources SOx: Coal Burning Coal contains 1-3% S S + O2  SO2 NOx: Combustion of fossil fuels Air contains 78% N N + O2  NO2 Using pH:  Using pH A solution is made in which 50 mg HCl(g) is dissolved in enough water to make a 100 mL solution. Assuming all the HCl dissociates into H+ and Cl- in water, what is the pH of this solution? 1. How many moles of HCl are there? 2. What is [HCl]? 3. What is [H+]? 4. What is the pH? Dissociation of water:  Dissociation of water [H+][OH-] = 1 x 10-14 M Pure water H OH H OH H OH H OH H OH H+ H+ OH- OH- [H+] = 1 x 10-7 M [OH-] = 1 x 10-7 M

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