I am reviewing the book Biochemistry Concepts and Connections by Appling, Cahill, and Mathews and I cannot understand why they divide by the hydrogen concentration by 10^-7.  Why not just leave it at the antilog(-8.1) over 1 M like the other concentrations?  I literally have see nothing else on the internet like this.

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  [1]: https://i.sstatic.net/Dnkrb.jpg