HCl aq H 2 O l o H 3 O aq Cl aq 100 ionization 056 M 0 0 K 1 056 M 056 M 056 M

Hcl aq h 2 o l o h 3 o aq cl aq 100 ionization 056 m

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HCl( aq ) + H 2 O( l ) o H 3 O + ( aq ) + Cl ( aq ) 100% ionization 0.56 M 0 0 K >> 1 0.56 M +0.56 M +0.56 M 0 0.56 M 0.56 M pH of a 0.56 M HCl solution: Strong bases : KOH( aq ) o K + ( aq ) + OH ( aq ) 100% ionization 0.024 M 0 0 K >> 1 – 0.024 M + 0.024 M + 0.024 M 0 0.024 M 0.024 M pH of a 0.024 M KOH solution: Example Problem : What is the pH of a 0.10 M Ca(OH) 2 solution? 1036 Chapter 18 15 of 51 Memorize these strong acids and bases: Strong Acids Strong Bases HCl Group 1 hydroxides (LiOH, NaOH,etc) HBr Ca(OH) 2 HI Sr(OH) 2 HNO 3 Ba(OH) 2 H 2 SO 4 HClO 4 Summary of pH calculations for Strong Acids and Strong Bases : Strong Acids, HA: [HA] = [H 3 O + ] pH = –log[H 3 O + ] pH = –log[HA] Strong Bases, B: For Group 1 Hydroxides For Group 2 Hydroxides [B] = [OH ] 2[B] = [OH ] pOH = –log[OH ] pOH = –log[OH ] pOH = –log[B] pOH = –log 2[B] 1036 Chapter 18 16 of 51 Weak Acids Strong acid: HCl( aq ) + H 2 O( l ) o H 3 O + ( aq ) + Cl ( aq ) 100% ionization 0.10 M 0 0 K >> 1 0.10 M +0.10 M +0.10 M 0 0.10 M 0.10 M pH = –log[0.10] = 1.00 Weak acid: HC 2 H 3 O 2 ( aq ) + H 2 O( l ) H 3 O + ( aq ) + C 2 H 3 O 2 ( aq ) < 100% ionization 0.10 M 0 0 K << 1 x + x + x ? ? ? [H 3 O + ] < 0.10 and pH > 1.00 Weak acids: Produced with a Trial Version of PDF Annotator -
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1036 Chapter 18 17 of 51 1036 Chapter 18 18 of 51 HA( aq ) + H 2 O( l ) H 3 O + ( aq ) + A ( aq ) K a = Example : Write the K a expression for HNO 2 : First, write the reaction: Then, write the K a expression: 1036 Chapter 18 19 of 51 p K a = 1036 Chapter 18 20 of 51 Factors Affecting Acid Strength H + ----A H + + A Since the bond between H and A is broken during the acid ionization process, factors that affect the strength and polarity of this bond also affect the strength of the acid. 1. Binary acids: Hydrogen and a nonmetal, HX Horizontal trend: in a given period (row): Example: H 2 S (K a = 9 x 10 –8 ) vs. HCl ( K a = large) In a given period, the greater the electronegativity of A, the stronger the acid, HA. Increases left to right across row Electronegativity: Acid strength: Produced with a Trial Version of PDF Annotator -
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1036 Chapter 18 21 of 51 Vertical trend: in a given group (column): Example: Group 17: Acid strength HF < HCl < HBr < HI Bond strength: 565 > 431 > 366 > 299 kJ/mol In a given group, the weaker the H A bond, the stronger the acid. Bond strengths decrease down a group in the periodic table as bond length increases. 1036 Chapter 18 22 of 51 Binary Acid Strength Trend: 1036 Chapter 18 23 of 51 2. Oxoacids H , O, and a third nonmetal, HOX Acid K a Acid K a Acid K a HClO 4 ~10 7 HBrO 4 ~10 6 HIO 4 1.4x10 1 HClO 3 ~10 3 HBrO 3 3.0 HIO 3 1.6x10 –1 HClO 2 1.12x10 –2 HClO 2.9x10 –8 HBrO 2.0x10 –9 HIO 2.3x10 –11 Compare HClO 4 ( K a = 107) to HClO ( K a = 2.9x10 –8 ): 1036 Chapter 18 24 of 51 Compare: HClO HBrO HIO The more electronegative the atom present in the molecule, the stronger the acid. Produced with a Trial Version of PDF Annotator -
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1036 Chapter 18 25 of 51 Weak Bases NaOH( aq ) o Na + ( aq ) + OH ( aq ) 100% ionization 0.10 M 0 0 K > > 1 0.10 M + 0.10 M + 0.10 M 0 0.10 M 0.10 M pOH = log[OH ] = [0.10] = 1; pH = 14 – pOH = 14 – 1 = 13 NH 3 ( aq ) + H 2 O( l ) NH 4 + ( aq ) + OH ( aq ) <100% ionization 0.10 M 0 0 K < < 1 x + x + x ? ? ?
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