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I'm trying to extract citric acid from squeezed lemons. After studying the subject, I found the following document on next URL.

http://www.staff.amu.edu.pl/~psorg/serp.pdf

Especially pages 68 - 69 are very interesting.

Does anybody know the reason for adding hydrochloric acid and sodium hydroxide on the end of page 68?

This looks very useless to me, since in this case the alkaline and acid neutralize each other.

Thanks in advance!

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    $\begingroup$ True, they would neutralize, and the authors actually did bother to emphasize that: "Then neutralize the solution with 2M NaOH..." That's the very point of it. If you could add just the right amount of acid on the first try, you probably wouldn't need this step, but that's hardly possible. $\endgroup$ – Ivan Neretin Aug 24 '16 at 11:40
  • $\begingroup$ Thanks for your comment. But why should you add hydrochloric acid and sodium hydroxide, after we already obtained calcium citrate? After the following step: "Stir for 15 minutes, then heat it to boiling and filter calcium citrate (Ca3C12H10O14) from the hot mixture on a Büchner funnel..." we could also go to the next steps on page 69, without adding an acid and alkaline? $\endgroup$ – ChemStudent Aug 24 '16 at 11:58
  • $\begingroup$ Theoretically, we could. But see, they are still adding acid there on p.69. $\endgroup$ – Ivan Neretin Aug 24 '16 at 12:07
  • $\begingroup$ Is this maybe a purification step? But which impurities are removed and on which chemical principle is this based? $\endgroup$ – ChemStudent Aug 24 '16 at 12:09
  • $\begingroup$ I have also found recipes, without the last step on page 68 (without adding HCl and NaOH). But I would like to know what the reason was. $\endgroup$ – ChemStudent Aug 24 '16 at 12:15

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