Cliffs AP Chemistry, 3rd Edition

Since H+from the acid reacts in a 1:1 mole ratio with OH–, the number of moles of H+fur-

nished by the acid must also be 0.00393.

.

.

equivalent mass /

moles of H

grams of acid

mol

g

0 00393 g mol

0 500

= + == 127

6. Referring to Appendix B, which indicator(s) would have been the most appropriate to use?
   Phenolphthalein would have been a good choice because the pH at the equivalence point
   falls within the range over which this indicator changes its color.


7. Does the solid acid appear to be monoprotic or diprotic and why?
   This acid appears to be monoprotic because the titration curve (see Figure 3 above) only
   shows one inflection point so far as plotted. Another end-point (equivalence point) is gen-
   erally hard to find, using only indicators above pH=10.5 since the indicator equilibrium
   reaction HInEH+-+=In K_iHIn 10 -^12 interacts and interferes.

Part III: AP Chemistry Laboratory Experiments