What is the citric acid concentration, [HCit], in the lemon juice?


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> The pH of lemon juice is about 2.1. What is the citric acid concentration, [HCit], in the lemon juice?
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I am given that $HCit \leftarrow \rightarrow H^+ + Cit^-$ and that $K\_a = 8.4 \times 10^{-4}$. 


$K\_a = \frac{[H+][Cit]}{[HCit]} = 8.4 \times 10^{-4}$, and $[H+]$ is $10^{-2.1}$. However, without knowing $[Cit]$, how can I get [HCit]? Any help would really be appreciated!




For any mono-protic acid, when the acid dissociates in water, every H+ created will create one CB-.



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> H-Cit <--> H+ + Cit-
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For each 1 H-Cit. 1 H+ and 1 Cit- is produced upon dissociation.
Therefore, the [H+] = [Cit-]


For a Ka expression, set these two [] equal to each other, and the expression for [H+]\*[Cit-] = x^2


Use this to determine the amount of [Cit-] created when you create x amount of [H+].


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