pH = pKa + log (CBA / CHA)
7.8 = 7.2 + log (CBA / CHA)
log (CBA / CHA) = 0.6
So:
CBA / CHA = 3.98
and CBA + CHA = 0.4
Solving this system of equations, we have:
CHA = 0.08M
CBA = 0.4 − CHA = 0.32M
"n(HA)=C_{HA}*V_{sol}=0.08M*6L=0.48mol"
"n(BA)=C_{BA}*V_{sol}=0.32M*6L=1.92mol"
"n(HA)+n(BA)=0.48mol+1.92mol=2.40mol"
Now we take 2.40 mol * 209.3 g/mol = 502 g of MOPS
and 1.92 mol/10M = 0.192L of 10M solution of NaOH (react in a 1 to 1 molar relation):
C7H15NO4S + NaOH = C7H14NO4SNa + H2O
After the reaction is complete, you dissolve this mixture up to 6L in a special flask with distilled water.
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