pH scale - with a special log

The http://webwork.rutgers.edu/webwork2_...0c5825b3f1.png scale for acidity is defined by http://webwork.rutgers.edu/webwork2_...6e536fbfa1.png where http://webwork.rutgers.edu/webwork2_...ba85997071.pngis the concentration of hydrogen ions measured in moles per liter (M).

A solution has a http://webwork.rutgers.edu/webwork2_...0c5825b3f1.png of 7.8.

Calculate the concentration of hydrogen ions in moles per liter (M).

The concentration of hydrogen ions is moles per liter

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okay so here's what i did

7.8 = -log10 (X)

10^7.8 = -X

seems like that's wrong though? any thoughts?