L16_AcidBase3_115b08

L16_AcidBase3_115b08 - L16: Polyprotic acids: H2SO4, H2SO3,...

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L16: Polyprotic acids: H 2 SO 4 , H 2 SO 3 , H 2 CO 3 , H 3 PO 4 , etc Several equilibria: H 2 SO 4 H + + HSO 4 - K a1 >100 HSO 4 - H + + SO 4 2- K a2 =1.2*10 -2 Note: hydrogen sulfate ion HSO 4 - is amphoteric; K a1 >> K a2 is very common ; If K a1 and K a2 are different by a factor 100 or more => can treat 2 equilibria sequentially
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When a 0.034 M H 2 CO 3 solution is prepared, what are the concentrations of HCO 3 - , CO 3 -2 and H + ? K a1 =4.3*10 -7 and K a2 =4.8*10 -11 . (1) H 2 CO 3 H + + HCO 3 - (2) HCO 3 - H + + CO 3 2- Main source of H + is step 1, because K a1 >>K a2 >>K w (this assumption will be checked later). (1) H 2 CO 3 H + + HCO 3 - Eq: 0.034- x x x x =1.2*10 -4 M=[H + ]=[HCO 3 - ] Assumption is valid! ] [ ] ][ [ 3 2 3 1 CO H H HCO K a + = ] [ ] ][ [ 3 2 3 2 + = HCO H CO K a 7 - 2 2 3 2 3 1 10 4.3 034 . 0 034 . 0 ] [ ] ][ [ = = = + x x x CO H H HCO K a
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When a 0.034 M H 2 CO 3 solution is prepared, what are the concentrations of HCO 3 - , CO 3 -2 and H + ? K a1 =4.3*10 -7 and K a2 =4.8*10 -11 . (1) H 2 CO 3 H + + HCO 3 - (2) HCO 3 - H + + CO 3 2- (1) H 2 CO 3 H + + HCO 3 - x = 1.2*10 -4 M=[H + ] = [HCO 3 - ] (2) HCO 3 - H + + CO 3 2- Eq: 1.2*10 -4 y 1.2*10 -4 + yy y =4.8*10 -11 = [CO 3 2- ]
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This note was uploaded on 07/22/2008 for the course CHEM 115b taught by Professor Reisler during the Spring '08 term at USC.

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L16_AcidBase3_115b08 - L16: Polyprotic acids: H2SO4, H2SO3,...

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