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# Lect w8 152 - ka and kb calculations_summary exercises_alg

## on Apr 01, 2011

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• Kb = 6.9e-4
• Kb = 6.9e-4

## Lect w8 152 - ka and kb calculations_summary exercises_algPresentation Transcript

• 1. What is the pH of a solution of 0.050 M (C 2 H 5 ) 2 NH?
• 2. What is the pH of a solution of 0.050 M HClO 4 ?
• Summary Activity 3. Label the following as acidic, basic, or neutral solutions: KCl NaNO 2 (CH 3 ) 2 NH 2 Cl
• Which of the following is the strongest acid? HClO 2 , HBrO 2 , HIO 2
• Which of the following is the strongest acid? H 3 N, H 2 O, HF
• What kind of substance is C 2 H 5 NH 2 ?
• Strong acid
• Strong base
• Weak Acid
• Weak base
• 1. What is the pH of a solution of 0.050 M (C 2 H 5 ) 2 NH? (K b = 4.9  10 -4 ) The approximation is invalid! 0.05/(4.9  10 -4 ) = 72  ICE Table (C 2 H 5 ) 2 NH + H 2 O  (C 2 H 5 ) 2 NH 2 + + OH - I 0.050 0 0 C -x +x +x E 0.050-x x x K b = [(C 2 H 5 ) 2 NH 2 + ][OH - ] = x 2 (C 2 H 5 ) 2 NH 0.050-x  quadratic x 2 + (4.9  10 -4 )x – (2.45  10 -5 ) = 0 x = 4.7  10 -3 = [OH - ] pOH = -log(4.7  10 -3 ) = 2.33 pH = 14 – 2.33 = 11.67
• 2. What is the pH of a solution of 0.050 M HClO 4 ? Easy!! HClO 4 is a strong acid, therefore [HClO 4 ] = [H 3 O + ] dissociated! [H 3 O + ] = 0.050 M pH = -log(0.050) pH = 1.30
• Summary Activity 3. Label the following as acidic, basic, or neutral solutions: KCl NaNO 2 (CH 3 ) 2 NH 2 Cl neutral basic acidic K + (cation of a strong base)  neutral Cl - (anion of a strong acid)  neutral Overall  neutral
• Summary Activity 3. Label the following as acidic, basic, or neutral solutions: KCl NaNO 2 (CH 3 ) 2 NH 2 Cl neutral basic acidic Na + (cation of a strong base)  neutral NO 2 - (anion of a weak acid )  basic Overall  basic
• Summary Activity 3. Label the following as acidic, basic, or neutral solutions: KCl NaNO 2 (CH 3 ) 2 NH 2 Cl neutral basic acidic (CH 3 ) 2 NH 2 + (cation of a weak base —4 groups attached to N)  acidic Cl - (anion of a strong acid)  neutral Overall  acidic
• Which of the following is the strongest acid? HClO 2 , HBrO 2 , HIO 2 Non-binary acids  must consider resonance or inductive effect not resonance 1) there are no possible resonance structures (already saturated) 2) all Lewis dot structures are equivalent inductive effect  ClO 2 - has Cl (which is more electronegative than Br or I). The Cl withdraws the electrons from the O atoms, stabilizing the anion  making the HClO 2 more acidic O—Cl—O : : : : : : : : O—Br—O : : : : : : : : O—I—O : : : : : : : :   
• Which of the following is the strongest acid? H 3 N, H 2 O, HF Binary acids  must consider electronegativity or size of the anion N  O  F moving left to right across periodic chart Therefore HF is strongest acid because its anion is the most electronegative atom in the group above. And the more electronegative the anion, the greater the ability to stabilize the anion, and therefore the stronger the acid
• What kind of substance is C 2 H 5 NH 2 ?
• Strong acid
• Strong base
• Weak Acid
• Weak base
There are 3 groups on the N, leaving the lone pair available. Therefore this amine is basic. N C 2 H 5 H H :