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+ Chemical reactions
+ Sodium hydroxide
+ Titration
+ Chemistry
+ Aspirin
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Maria Pugliese

What is the balanced equation for the back titration of aspirin and NaOH?

Mbanginu Aurelie Kfe  Follow

Aspirin ist just the common name for acetylsalicylic acid. It is a benzoic acid, substituted in the ortho position with an acylated alcohol (actually a phenol) function.

Thus, there are two reactions that can occur between aspirin and NaOH: the faster will be deprotonation of the acid function, so you'll get sodium acetylsalicylate. This is actually what is present in many aspirin formulations.

The other is saponification of the acetyl function. This function is an ester. In the case of aspirion, it is the salicylate ester of acetic acid. Salicylate is the common name of 2-hydroxy-benzoic acid. So if you saponify the acetyl, you will get sodium acetate and sodium salicylate.

The first reaction is complete and fast at room temperature. The second is slower, and requires prolonged heating, and higher NaOH concentration.

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Christian Acevedo  Follow

In a back titration reaction there has to be 2 titrations meaning 2 equations

The first reaction is to add an excess of NaOH to the aspirin - which is acetylsalicylic acid - C8H7O2COOH. The NaOH reacts with all the acid according to the following equation .

C8H7O2COOH + NaOH → H2O + C8H7O2COONa

You record the volume of standard NaOH solution used

You then determine the excess unreacted NaOH by (back) titrating with standard HCl . From the volume of HCl required you can determine the moles of unreacted NaOH and hence the NaOH used in the neutralisation of the aspirin .

The back titration equation is

NaOH + HCl → NaCl + H2O .

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