POST-LAB QUESTIONS Show all work for full credit. 1. Why did you have to remove

Question

POST-LAB QUESTIONS Show all work for full credit. 1. Why did you have to remove CO, from your partially neutralized stomach acid before the titration? (This was done by heating the solution gently.) 2. Why was methyl red used as an indicator in this experiment rather than phenolphthalein? Based upon the data collected by your lab section, are extra strength antacids more cost effective than the regular strength tablets? (Clearly explain your answer in terms of cost and volume of acid neutralized.) 3.

Explanation / Answer

Q1) CO2 +H2O <-->H2CO3

The stomach acid is HCl, it my have dissolved CO2 which is partially in H2CO3 or carbonic acid form due to the above written reaction equilibrium existing in the acid.This H2CO3 also gets neutralized with NaOH and increase the volume of titrant (NaOH) if not removed.Higher volume of titrant may result in higher value of molarity of stomch acid in calcultions.

M(acid)*V(acid)=M(NaOH)V(NaOH)

M(acid)=M(NaOH)V(NaOH)/V(acid)

Q2)Methyl red works at the pH range of 4.2 to 6.2 ,but phenolpthalein works at the pH range above 9.0

The antacid tablet components gives the solution a final pH between 4 and 6 ,so methyl orange is a suitable indicator for this titration, giving pinkish red in acid and yellow color in basic medium of pH=6 and above

Q3) For a stronger antacid , more volume of stomach will be neutralized for the same dose of the antacid,so a lesser dose is required to be administered ,making it cost-effective.

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