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unit 8 must knows

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what is a buffer ☝️ Click to use flashcards

unit 8 must knows

12 Flashcards 0 recently 0/10

Elias A

unit 8

Physical chemistry

Terms

what is a buffer
 solution that is resistant to a small pH change, it has to contain a weak acid or base pared with its conjugate salt(Na+, H3O-, etc...) and it creates neutral compounds, keeping pH relatively stable
how do you calculate a buffer's pH
 pH = pKa + log [A-]/[HA] ---> acids pOH = pKb + log [BH+]/[B] ---> bases the conjugate salt is on top, and the bottom is either the base or the acid assume there is a limiting and excess reagent (because it will contain either a strong acid or base)
in what range are buffers effective
 within 1 pH of its pKa, up or down
pH + pOH =
 14 always!!
H2O pH is always...
 7, could be acid (pH) or base (pOH)
Kw =
 1.0 x 10^-14 at 25 C or 298 K
weak acid-strong base reaction
 HA(aq) + OH- --> A-(aq) + H2O(L) if weak acid is in excess --> a buffer --> Hendeson Hasselbalch equaiton if strong base is in excess, the moles of excess hydroxide ions is used for pH if acid and base are equimolar then the equilibrium concentr
strong acid-weak base reaction
 if weak base is in excess --> a buffer --> Hendeson Hasselbalch equaiton if strong acid is in excess, the moles of excess acid are used to determine pH if acid and base are equimolar then the equilibrium concentrations are used to determine pH
maximum buffering capacity
 pH = pKa
how to increase/decrease buffering capacity
 increasing/decreasing concentrations of buffer components, but keeping the ratios constant (if you don't it'll change the buffer capacity for either acid or base respectively)
equivalence point
 straight line up part of graph #miles of titrant = #moles of analyte concentration and volume of titrant is then used to determine concentration of analyte
strong acid strong base equivalence point
 pH = 7 @ 25 C / 298 K