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9

The colour of black tea is given by a complex mixture of theaflavins and thearubigins. These compounds are formed by enzymatic oxidation and condensation of polyphenols of green tea, typically of gallocatechin and epigallocatechin gallate ( EGCG ) Basic dissociated forms of these compounds have strong absorption of visible light due to delocalization of ...

3

As pointed out in the comments, the concept of pH as a thermodynamic property of nanodroplets does not quite make sense unless the nanodroplets are in equilibrium (stable). If they are in equilibrium you can still apply the equation $$\textrm{pH}=-\log_{10}(a_{\ce{H+}})$$ but now you have to be aware that the activity will be influenced by surface (and ...

2

Please be aware that adding salt changes the ionic strength of your solution. Therefore, the activity $a_\mathrm H$ of $\ce{H+}$ is changed. This changes $\mathrm{pH}=-\log_{10}(a_\mathrm H)$. In a 1 molar $\ce{NaCl}$ solution ($I\approx 1\ \mathrm{mol/l}$) the Debye-Hueckel (DH) approximation gives a shift of the activity by around 0.5 pH units (compared to ...

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