Class #4 Solutions and Ions CHEM 107 L.S. Brown Texas A&M University Pure Substances Pure substance: described completely by a single chemical formula Fixed composition 1
Mixtures Combination of 2 or more pure substances Variable composition Full description requires knowledge of relative amounts of each component Solutions Homogeneous mixtures, 2 or more components Often liquids, but can also be gases or solids Solvent: major component Solute: minor component Aqueous solution: solvent = water 2
Concentrated and Dilute Solutions 4.57 g CuSO 4 in 100 ml 0.54 g CuSO 4 in 100 ml Concentration Describes relative amounts of solution components We ll usually use MOLARITY: molarity = moles of solute liters of solution Other units are also possible 3
Molarity Calculation Calculate the molarity of the CuSO 4 solutions we saw earlier. 1: 4.57 g CuSO 4 in 100 ml 2: 0.54 g CuSO 4 in 100 ml Ions Ions: atoms or groups of atoms with electric charge Cations: positive charge Anions: negative charge 4
Monatomic Cations Make from neutral atoms by removing electrons Metals, often from first 2 columns of periodic table Na à Na + + e Periodic Table IA VIIA 0 (1) (17) (18) 1 1 2 H IIA IIIA IVA VA VIA H He 1.008 (2) (13) (14) (15) (16) 1.008 4.003 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 6.941 9.012 10.81 12.01 14.01 16.00 19.00 20.18 11 12 13 14 15 16 17 18 VIIIB Na Mg IIIB IVB VB VIB VIIB IB IIB Al Si P S Cl Ar 22.99 24.31 (3) (4) (5) (6) (7) (11) (12) 26.98 28.09 30.97 32.07 35.45 39.95 (8) (9) (10) 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 39.10 40.08 44.96 47.88 50.94 52.00 54.94 55.85 58.93 58.69 63.55 65.39 69.72 72.61 74.92 78.96 79.90 83.80 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 85.47 87.62 88.91 91.22 92.91 95.94 (98) 101.07 102.91 106.42 107.87 112.41 114.82 118.71 121.75 127.60 126.90 131.29 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 132.91 137.33 138.91 178.49 180.95 183.85 186.21 190.2 192.22 195.08 196.97 200.59 204.38 207.2 208.98 (209) (210) (222) 87 88 89 104 105 106 107 108 109 Fr Ra Ac Rf Ha Sg Ns Hs Mt (223) (226) (227) (261) (262) (263) (262) 1.1 58 1.1 59 1.1 60 1.1 61 1.1 62 1.1 63 1.1 64 1.1 65 1.1 66 1.1 67 1.1 68 1.1 69 1.0 70 1.2 71 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 140.12 140.91 144.24 (145) 150.36 151.97 157.25 158.93 162.50 164.93 167.26 168.93 173.04 174.97 1.2 90 1.3 91 1.5 92 1.3 1.3 94 1.3 95 1.3 96 1.3 97 1.3 98 1.3 99 1.3 100 1.3 101 1.3 102 1.5 103 93 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 232.04 231.04 238.03 (237) (244) (243) (247) (247) (251) (252) (257) (258) (259) (260) 5
Monatomic Anions Make from neutral atoms by adding electrons Nonmetals, often halogens Cl + e à Cl Periodic Table IA VIIA 0 (1) (17) (18) 1 1 2 H IIA IIIA IVA VA VIA H He 1.008 (2) (13) (14) (15) (16) 1.008 4.003 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 6.941 9.012 10.81 12.01 14.01 16.00 19.00 20.18 11 12 13 14 15 16 17 18 VIIIB Na Mg IIIB IVB VB VIB VIIB IB IIB Al Si P S Cl Ar 22.99 24.31 (3) (4) (5) (6) (7) (11) (12) 26.98 28.09 30.97 32.07 35.45 39.95 (8) (9) (10) 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 39.10 40.08 44.96 47.88 50.94 52.00 54.94 55.85 58.93 58.69 63.55 65.39 69.72 72.61 74.92 78.96 79.90 83.80 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 85.47 87.62 88.91 91.22 92.91 95.94 (98) 101.07 102.91 106.42 107.87 112.41 114.82 118.71 121.75 127.60 126.90 131.29 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 132.91 137.33 138.91 178.49 180.95 183.85 186.21 190.2 192.22 195.08 196.97 200.59 204.38 207.2 208.98 (209) (210) (222) 87 88 89 104 105 106 107 108 109 Fr Ra Ac Rf Ha Sg Ns Hs Mt (223) (226) (227) (261) (262) (263) (262) 1.1 58 1.1 59 1.1 60 1.1 61 1.1 62 1.1 63 1.1 64 1.1 65 1.1 66 1.1 67 1.1 68 1.1 69 1.0 70 1.2 71 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 140.12 140.91 144.24 (145) 150.36 151.97 157.25 158.93 162.50 164.93 167.26 168.93 173.04 174.97 1.2 90 1.3 91 1.5 92 1.3 1.3 94 1.3 95 1.3 96 1.3 97 1.3 98 1.3 99 1.3 100 1.3 101 1.3 102 1.5 103 93 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 232.04 231.04 238.03 (237) (244) (243) (247) (247) (251) (252) (257) (258) (259) (260) 6
2 or more atoms Polyatomic Ions Held together by chemical bonds Electrically charged Cations or anions NH 4+, H 3 O +, NO 3, SO 4 2 See table in textbook for more Ionic Compounds Anions & cations, charges balancing Coulomb force (attraction of opposite charges) Crystalline solids, high melting points. 7
Structure of Ionic Crystals In an ionic crystal, positive and negative ions are arranged in an orderly array. This is what leads to the crystalline appearance. NaCl Crystal Structure 8
Ionic Compounds in Solution Many ionic compounds dissolve in water Properties in solution different from in solids Many ionic solutions conduct electricity Ionic compounds in Solution Conductivity implies free ions. Soluble ionic compounds dissociate in solution NaCl(s) à Na + (aq) + Cl (aq) Overall solution is still electrically neutral! 9
Chemistry in Solution Ionic solids usually don t react readily with one another But solutions often react very rapidly Difference is due to the dissociation in solution Solution Chemistry: KI + Pb(NO 3 ) 2 10
Solution Chemistry: KI + Pb(NO 3 ) 2 Solution Chemistry: KI + Pb(NO 3 ) 2 11
Equations? Molecular Equation 2 KI + Pb(NO 3 ) 2 à 2 KNO 3 + PbI 2 Drawback is that solution does NOT contain ANY molecules of KI or Pb(NO 3 ) 2 Ionic Equations Solutions contain free ions KI(s) à K + (aq) + I (aq) Pb(NO 3 ) 2 (s) à Pb 2+ (aq) + 2 NO 3 (aq) Products? KNO 3 (s) à K + (aq) + NO 3 (aq) PbI 2 (s) à (NOT SOLUBLE) 12
TOTAL Ionic Equation Show ALL ions present: 2 K + + 2 I + Pb 2+ + 2 NO 3 à 2 K + + 2 NO 3 + PbI 2 (s) Note K +, NO 3 on both sides Spectator Ions NET Ionic Equation Don t write spectators ions 2 I (aq) + Pb 2+ (aq) à PbI 2 (s) Only shows reacting ions Simpler looking equation; more commonly used 13