ph = - log [H3O+] Example: ph 7 = - log [ 1 x 10-7] [H3O+] = mole/liter units ph values are unitless

Transcription

1 E4 Acids, Bases, and Salts Oct and Oct. 2728* Session One of two session lab Complete Parts 1 and 2 in lab. Part 1. Structure and AcidBase Properties Q. Are properties of a compound predictable from its chemical formula? If time allows, start or complete Part 3. Prelab report (page 120) correction: Question 3 prelab report correction: Based on the above p data, identify the strongest from the list of : ousehold s ousehold s * Fall break Oct NO chem.125/126 activities Oct Part 1. Structure and AcidBase Properties Information Acids and Bases usually contain O,, and another element (X). Teams will be provided with compounds labeled with the formula XcOab (X= some element; a, b, and c = some number) Determine if the p of XcOab compounds and the or properties can be predicted from: The number of oxygen and/or hydrogen atoms in XcOab compounds? The position of element X in the Periodic Table The electronegativity of element X? Determine if compounds with the formula XcOab are s or s by measuring the p Part 1 Data collection p Determine the p of XcOab compounds Example: LIO BO33 C2O24 NO3 p = log [3O+] Example: p 7 = log [ 1 x 107] [3O+] = mole/liter units p values are unitless 1

2 p and [ 3 O + ] DIGIT/S LEFT of the p decimal point J = POWER of TEN by which the hydronium concentration value is multiplied. [ 3 O + ] p If p = 3.27, [ 3 O + ] = [? ] x 10 3 [ 3 O + ] p = 1 reflects a ten fold change in [ 3 O + ]; p = 2 reflects a hundred fold change in [ 3 O + ], etc. As [ 3 O + ] increases, p decreases: p p measurement p ACID = p < p paper p indicator p meter Universal indicator BASE = p > 7 Part 1 Data analysis Based on the p, indicate if each compound is an or. X c O a b compounds and AcidBase formulas The formulas for s are written in the form b X c O a. p LiO 1 BO 3 3 C 2 O 2 4 NO 3 Acid/ Rewrite the formula to reflect the or p 2 CO 3 (carbonic ) 3 PO 4 (phosphoric ) 2

3 XcOab compounds and AcidBase formulas Rewrite the formulas to reflect if each compound is an or The formulas for s are written as Xc(O)n. p 1 LiO BO33 C2O24 NO3 NaO Mg(O)2 Ca(O)2 Acid/ LiO 3BO3 C23O2 NO3 N4O Q. Are / characteristics dependent on: the number of atoms? If so, how? p 1 LiO 3BO3 C23O2 NO3 Q. Are / characteristics related to: the electronegativity of the element X? If so, how? Acid/ LiO 3BO3 p Acid/ 1 Electronegativity Li = C23O2 C= NO3 N= B= NO. Answer: Electronegativity of X vs. p of XcOab compounds Electronegativity of the elements* IA IIA IIIB IVB VB VIB VIIB Li Be Na 0.9 K 0.8 Rb 0.8 Cs 0.7 Fr 0.7 Mg 1.2 Ca Sr Ba 0.9 Ra VIIIB 11 IB LiO vs. 3BO3vs. C23O2vs NO3? B C N O F Sc Y 1.2 La Lu Ac 1.1 = Metalloids Ti Zr 1.4 f Th V Nb Ta Pa Cr Mo W U Mn Tc Re Np = Nonmetals Fe Ru Os No Co Rh Ir Ni Pd Pt Cu Ag Au IIB IIIA IVA VA VIA VIIA Zn Cd g Al Ga In Tl Si Ge Sn Pb P As Sb Bi S Se 2.4 Te Po Cl Br 2.8 I At Q. Are / characteristics related to: the electronegativity of element X? If so, how? LiO 3BO3 p 1 Acid/ Electronegativity of X C23O2 NO3 Yes. Answer: The higher the electronegativity of X the lower the p = Metals 3

4 Bronsted Definition of Acids and Bases Acid characteristics are related to the electronegativity of element X in X c O a b compounds Why? Lets explore the definition of an. An is a proton ( + ) donor forms hydronium ions. Cl + O + Cl + O A is a proton ( + ) acceptor forms hydroxide ions. O + : N 3 N O Lewis Definition of Acids and Bases An is an electron pair seeker. Cl + O A is an electron pair donor + Cl + O O + : N 3 N O AcidBase Strength and Structure If in a compound is a bare proton it will be an electron pair seeker and readily bond to water to form [ 3 O] + Example: ClO is a bare proton when bonded to an O atom, which in turn is attached to highly electronegative Cl in ClO ClO + O 3 O+ + ClO 100% ionization O The higher the electronegativity of element X in X c O a b compounds: The lower the p of the compound The more likely the compound is a proton donor. p Acid/ Electronegativity of X LiO 1 3 BO 3 C 2 3 O 2 NO 3 Electronegativity of X vs. p of X c O a b compounds Electronegativity of the elements* IA IIA IIIB IVB VB VIB VIIB VIIIB IB IIB IIIA IVA VA VIA VIIA LiO vs. 3 BO 3 vs. C 2 3 O 2 vs NO 3 > electronegativity and < p Li Be B C N O F Na Mg Al Si P S Cl K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Cs Ba La f Ta W Re Os Ir Pt Au g Tl Pb Bi Po At Lu 2.4 Fr Ra Ac Th Pa U Np No = Metalloids = Nonmetals = Metals 4

5 AcidBase Ionization The production of hydronium (or hydroxide ions) is solvent and concentration dependent. + + O anion : Addition of water to C 2 3 O 2 + O When comparing (or ) strength, concentration of the solutions must be considered Q. Indicate the strength of C 2 3 O 2 and NO 3 p Acid/ Electronegativity of X LiO 1 3 BO 3 C 2 3 O 2 NO 3 Answer: NO 3 > C 2 3 O 2 [ 3 O + ] p Acid Strength and p Stronger s donate protons/ionize to a greater extent than weak s. Stronger s exhibit a lower p than equimolar concentrations of weaker s. Example M NO 3 = p M C 2 3 O 2 = p Strength: NO 3 > C 2 3 O 2 Acid strength, p and structure Q. The electronegativity of N = and C =. Predict the comparative rate of reaction of 5 NO 3 and 5 M C 2 3 O 2 with zinc: Zn (s) (aq) = Zn 2+ (aq) + 2(g) Rate: > NO 3 C 2 3 O 2 AcidBase Strength and % Ionization AcidBase Strength and % Ionization % Ionization % ionization = [ 3 O+ ] X 100% [] i % ionization = [O ] X 100% [] i Value in numerator determined from p = 100% I m strong! You are weak! = < 100% 5

6 Q.Your team determines that p M NO 3 = p. What is its % ionization? [ 3 O + ] X 100% [] i [0.01] x 100% = 1000% [0.001] = % ionization NO 3 % ionization cannot be greater than 100%; there is likely an error in the p or concentration. [ 3 O + ] p Check p data for errors Q. Your team determines that M NO 3 = p. You correctly respond, your p reading must be wrong! Why? If ionizes completely: NO O 3 O + + NO M M M Answer: [ 3 O + ] cannot be more (more, less) than M and p cannot be less (more, less) than p. Q. The textbook figure below depicting p and strength is misleading. ow? p Acid strength Acid strength cannot be determined d only on p p AND sample concentration must be known Example 10 4 M ClO 4 (strong ) = p 4 Part 2. Conjugate AcidBase Pairs Conjugate s and s differ by one proton. Conjugate of CO 3 is 2 CO 3 Conjugate of CO 3 is CO 3 2 Lab Compare the p of conjugate s (0.10 M s) and conjugate s (0.10 M sodium salts.) \ Conjugate AcidBase Pairs Conjugate AcidBase Pairs Exhibit predictable p relationships Canada Dry Canada Dry p 2 CO 3 (aq) versus CO 3 (aq) versus CO 3 2 (aq)? p 2 CO 3 (aq) versus CO 3 (aq) versus CO 3 2 (aq) Indicator p scale p increase 6

7 Titration (Part 3) A procedure for determining the unknown concentration of an (or ) Q. ow many ml of 0.10 M NaO will be required to neutralize 5.0 ml of 0.10 M oxalic? Oxalic OOCCOO + 2 NaO 2COONa + 2O 2 mol of NaO is required to neutralize one mol of oxalic : 2 (mmol ) = mmol 2 (5.0 ml 0.10 M) = x ml 0.10 M = 10 ml of 0.10 M NaO Any Questions? Contact nkerner@umich.edu 7