<P> An alternative scale, the' free scale', often denoted' pH', omits this consideration and focuses solely on (H), in principle making it a simpler representation of hydrogen ion concentration . Only (H) can be determined, therefore (H) must be estimated using the (SO) and the stability constant of HSO, K: </P> <Dl> <Dd> (H) = (H) − (HSO) = (H) (1 + (SO) / K) </Dd> </Dl> <Dd> (H) = (H) − (HSO) = (H) (1 + (SO) / K) </Dd> <P> However, it is difficult to estimate K in seawater, limiting the utility of the otherwise more straightforward free scale . </P>

Where do acids exist on the ph scale