CH301 - Type2.base - page 1 TYPE 2 (base buffer) ( both B...

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TYPE 2 (base buffer) ( both B and BH + are put into solution ) For a weak base (B) in water: B + H 2 O OH - + BH + For a salt, BHX, of the weak base (B) in water: BHX (s) + H 2 O BH + + X - (100% ionization!!!, and X - - is some anion of a strong acid - it does nothing) NOTICE: There are now TWO sources for the ion BH + . When there is more than one source for an ion in solution, this is called the COMMON ION EFFECT. Please be VERY aware that the main source for the ion, BH + , is from the salt and not from the base. This is the key to understanding TYPE 2 problems. Here, the two reactions BHX (s) are shown intersecting + at the point of the H 2 O common ion. 100 % forward X - this ion does NOTHING in aqueous solution! + B + H 2 O OH - + The following equilibrium condition still applies: K b = [OH ± ][BH + ] [B] Now let C B be the analytical concentration (label) of the weak base B, and C BH+ be the label concentration of the salt of the weak base BHX. Our Equilibrium "ICE" Table [B] [OH - ][ B H + ] initial C B 0 C BH + change – x + x + x equilibrium C B – x x C BH + + x K b = x ( C BH + + x ) ( C B
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CH301 - Type2.base - page 1 TYPE 2 (base buffer) ( both B...

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