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Acids and Bases Acids Acids and Bases Dr.Gergens - SD! Mesa College • General Properties Periodic Trends • Acid - Base (Strong versus Weak) • Acid - Base Conjugates • Reactions • pH Scale • Solution Stoichiometry and Titration • Overall Review of Basic Principles Acids MOST acids in the world are Weak Organic Acids • taste sour (vinegar, vitamin C, citric acid, folic acid) • feel sticky BLUE (litmus) to red … acid • turn blue litmus indicator paper (acid) to red • often have H listed first in their chemical formula strong acid car battery #1 stomach acid Coke & Pepsi vinegar HClO4 > H2SO4 > HCl > HNO3 >> H3PO4 > HC2H3O2 perchloric sulfuric hydrochloric nitric phosphoric acetic acid acid acid acid acid acid • often react with metals to produce hydrogen gas 1 Mg (s) + 2 HCl (aq) 1 MgCl2 (aq) + 1 H2 (g) atom metal strong acid ionic salt covalent (zero charge) • strong acids react with strong base to give salt and water 1 NaOH (aq) + 1 HCl (aq) 1 NaCl (aq) + 1 H2O (l) ionic salt base strong acid ionic salt weak acid (metal hydroxide) 1 Acids HClO4 > H2SO4 > HCl > HNO3 >> H3PO4 > HC2H3O2 hydrogen listed first Acids hydrogen-nonmetals H—X as a gas aqueous solution hydrogen perchlorate perchloric acid dihydrogen sulfate sulfuric acid hydrogen chloride hydrochloric acid aqueous solution hydrogen nitrate nitric acid acid dissolved in H2O aqueous acids trihydrogen phosphate phosphoric acid suffix name change hydrogen acetate acetic acid suffix -ate changes to —ic oxy acids hydrohalic acids O atomic acids H—O–X O H—X O Bases • taste bitter (shampoo, soap, baking soda, bleach) • feel slippery (saponify the oils in your skin to form soap) • turn red litmus to blue (base) - • sometimes have hydroxide ion OH given in their formula NaOH (drano), Ca(OH)2 (added to orange juice), Mg(OH)2 (milk of magnesia) • weak bases react with water to form hydroxide ion at equilibrium + – 1 NH3 (g) + 1 H2O (l) 1 NH4 (aq) + 1 OH (aq) covalent weak acid ammonium ion hydroxide ion weak base • strong acids react with strong base to give salt and water 1 NaOH (aq) + 1 HCl (aq) 1 NaCl (aq) + 1 H2O (l) strong base strong acid ionic salt water ionic salt pH = 7 2 Acid-Base Trends, Conjugates, and Reactions Dr. Gergens - SD Mesa College Periodic Trend ACIDS conjugate bases acidity increases basicity increases – – - - CH4 NH3 H2O H-F CH3 NH2 OH F – - - PH3 H2S H-Cl PH2 SH Cl acidity basicity increases increases - H-Br Br - H-I I Evaluating Acid-Base Reactions Definitions (relative strength to produce weaker acid) — – H—I + OH I + H2O – - SH + H2O H2S + OH + - NH3 + H-Cl NH4 + Cl •• •••• N H Predicting Proton-Transfer Products H O H H - H CH3 + H2O - HO + H S 2 H ⊕ •• •••• - N O NH2 + HBr H H H H NH3 + HF Can you name all the ions on molecules on this handout? Periodic Trend for increasing Acid Strength (across a period) Periodic Trend ACIDS acidity increases CH4 NH3 H2O H-F Electronegativity increases within a row PH3 H2S H-Cl Electronegativity increases within a row acidity increases H-Br H-I The more electronegative atom produces a more polar H-X bond Electronegativity Trend F > O > N > Cl > Br > I > S > C > H Foncl Brisch 3 Periodic Trend for increasing Acid Strength (down a family) Periodic Trend ACIDS acidity increases CH4 NH3 H2O H-F H F PH3 H2S H-Cl acidity increases Acidity Increases H-Br Down a family H-I H I Atom size increases going down a family with in “n” shells. A larger atoms afford longer H–X bond. Longer covalent bonds are more easily broken. Use the Periodic Trend for increasing acid strength to make your prediction Which is the stronger acid and why? HCl or HI I is a larger atom with a more easily broken H-I bond H2O or H2S S is a larger atom with a more easily broken H-S bond H2S or HCl Cl is a more electronegative atom; more polar bond 4 Periodic Trend for increasing conjugate base strength For every Acid, there is a conjugate base + To draw a conjugate base, just remove a H from its acid formula conjugate bases basicity increases ACID Conjugate base – – - - CH3 NH2 OH F _ H-I becomes I – - - PH2 SH Cl _ basicity H-Br becomes Br increases - Br _ H-Cl becomes Cl - I _ H-F becomes F _ H O becomes OH Note: basicity for these conjugate base 2 is the reverse of the acidity trend _ NH3 becomes NH2 _ CH4 becomes CH3 weakest acid strongest base Use the Periodic Trend for increasing conjugate base strength to make your prediction Which is the stronger base? _ _ Cl or I _ _ HO or HS _ _ HS or Cl 5 Definitions Know these definitions!!!!!! •• •••• N H Bronsted-Lorwy Bronsted-Lowry proton acceptor H O H H proton donor H Which definition best H ⊕ •• •••• N describes the reaction on H O H H the right? H Evaluating Acid-Base Reactions (relative strength to produce weaker acid) — – H—I + OH I + H2O Acid Base conjBase conjAcid – - SH + H2O H2S + OH Base Acid conjAcid conjBase + - NH3 + H-Cl NH4 + Cl Base Acid conjAcid conjBase 1) The first questions to ask in evaluating the preferred side of a proton transfer reaction: A) Which is the Acid? (acids generally have H listed first in their formula), and are the proton donor on the left side of the equation. B) Which is the Base? (bases can be anions or ionic salts, NaSH, KOH, LiCH3), and are the proton acceptor on the left side of the equation, including ammonia, NH3 2) The second question to ask in : Where is the conjugate base? The conjugate base shown on the right hand side of the reaction is the species formed from the Acid with a hydrogen ion missing. Where is the conjugate acid? the conjugate acid shown on the right hand side of the reaction is the species formed from the Base with a hydrogen ion added. 6 Evaluating Acid-Base Reactions (relative strength to produce weaker acid) — – H—I + OH I + H2O Acid Base conjBase conjAcid – - SH + H2O H2S + OH + - NH3 + H-Cl NH4 + Cl 3) Using our period trend for acidity and conjugate base strength, we can make an educated decisions regarding relative strength for our acids and bases in each reaction. 4) Our reaction arrow points to the weaker side of equilibrium. Periodic Trend ACIDS acidity increases conjugate bases basicity increases HI > H2O CH4 NH3 H2O H-F – – - - CH3 NH2 OH F - - PH OH > I – - - 3 H2S H-Cl PH2 SH Cl acidity basicity increases increases - H-Br Br - I H-I Evaluating Acid-Base Reactions (relative strength to produce weaker acid) — – H—I + OH I + H2O – - SH + H2O H2S + OH Base Acid conjAcid conjBase + - NH3 + H-Cl NH4 + Cl Our reaction arrow points to the weaker side of equilibrium. Periodic Trend ACIDS acidity increases conjugate bases basicity increases H2S > H2O CH4 NH3 H2O H-F – – - - CH3 NH2 OH F - - PH OH > SH – - - 3 H2S H-Cl PH2 SH Cl acidity basicity increases increases - H-Br Br - I H-I 7 Evaluating Acid-Base Reactions (relative strength to produce weaker acid) — – H—I + OH I + H2O Demonstrated in class – An ionic salt formed!!!!! - SH + H2O H S + OH It 2appeared as smoke. + - NH3 + H-Cl NH4 + Cl Base Acid conjAcid conjBase Our reaction arrow points to the weaker side of equilibrium. Periodic Trend ACIDS acidity increases + conjugate bases basicity increases HCl > NH4 CH4 NH3 H2O H-F – – - - CH3 NH2 OH F - PH NH > Cl – - - 3 H2S H-Cl 3 PH2 SH Cl acidity basicity increases increases - H-Br Br - I H-I Predicting Proton-Transfer Products - – CH3 + H2O CH + HO Base Acid conj Acid4 conj Base - – HO + H2S H O + HS Base Acid conj 2Acid conj Base - – NH2 + HBr NH + Br Base Acid conj Acid3 conj Base + – • NH + HF NH + F • 3 4 Base Acid conj Acid conj Base Let me demonstrate the ionic salt formed!!!!! Make Smoke?!?!?!?!?!?! 8 Acidic Oxides (nonmetal oxide molecules) nonmetal oxide molecules CO2 H CO The reaction of the oxides on the left 2 3 added to water produces SO3 H SO these acids on the right 2 4 NO HNO3 Can you draw the Lewis dot structures for all of these compounds? Begin by counting valence electrons. Remember, acids containing oxygen have an. H attached to an O make a table : O : 2H x 1 = 2 . .| . 4O x 6 = 24 H-O-S-O-H 1S x 6 = 6 . | . 32 VE : . .O : Basic Oxides (metal oxides ionic salts - nonmolecules) metal oxide nonmolecules Na2O NaOH The reaction of the oxides on the left MgO added to water produces Mg(OH)2 these ionic base salts on the right CaO Ca(OH)2 Can you draw the visual representation for all these compounds? 2- Na+ O Na+ Na+ OH1- 9 Acid-Base reactions of Carbonates ionic carbonate salts NaHCO3 The reaction of these carbonates CO on the left 2 MgCO3 & added to acid produces H O carbon dioxide gas and H O 2 CaCO3 (marble) 2 Predict the products of these reactions and balance the reaction: 1 NaHCO 3 + 1 HCl ----------> 1 NaCl + 1 H 2 O + 1 CO2 1 MgCO 3 + 1 H 2 SO 4 ----------> 1 MgSO 4 + 1 H 2 O + 1 CO2 1 CaCO 3 (marble) + 2 HNO 3 ----------> 1Ca(NO 3 ) 2 + 1 H 2 O + 1 CO2 10 —(pH value) [H+] = 10 + pH value = —log10 [H ] Kw = [H+] [OH–] 11 [H+] = 10—(pH value) + pH value = —log10 [H ] Kw = [H+] [OH–] Kw = 1 EE -14 12 H O Cabbage Juice as a pH indicator H C O C C H H H ⊕ C C - O C O Cl C C C C H Demonstration H C C C H C C O cyanidin O H H (red cabbage indicator) H Stoichiometry & Titration Watch the video on titration linked below http://homework.sdmesa.edu/dgergens/chem100L/titration/titration.html 13.
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