pH Levels for Chemistry Dummies

Every one in a while we run across a nicely-polished bit of freelancery that appears, on the surface at least, to be a well-done job of rewording something authoritative. Closer inspection, however, will reveal the cracks below the surface... one of the most frequent deficiencies of an otherwise serviceable copy-reword-paste job is that the writer depended on a single source, or sources of limited scope. For instance, we once found a pine tree ID guide that reworded a biology lab exercise for identifying the trees on a single college campus. Today's nominee does pretty much the same: she's Cassandra Tribe, writing for Sciencing.com on the topic of "What Variables Affect pH Levels?"

We're always concerned when someone refers to pH the way Tribe introduces the concept in her opening paragraph:

"Maintaining the correct pH level in a pool, aquarium, soil or even the human body requires frequent testing and correction. PH [sic] is the measure of the balance of acids and alkalis in the fluid or soil."

We strenuously object to her definition: pH is not "the measure of the balance of acids and alkalis"; it is a measure of the concentration of hydrogen ions in solution. The phrase "balance of acids and alkalis" makes no friggin' sense except to someone babbling about a diet.

We looked, and (at least) two of Cassandra's references were pitches for that "alkaline diet" thing; a fad that was hot at the time she wrote the post. A couple discuss pH levels in aquariums and/or pools and spas. Unfortunately, Tribe pulled most of her "variables" from a primer on stream water analysis. That's why her list includes "rocks, soil, coral..."

Whatever the case, Tribe rattled off an extensive list of "variables"; almost all of which are external influences and specific to one or two applications. The chemistry of the bedrock and soil may change stream pH; dissolved CO₂ affects the pH of sea water; chlorine affects the pH of pool and spa water, as might airborne contaminants; air pollution affects the pH of rain.

All of those are more or less true, but it's likely that none of them (except perhaps CO2) is the correct answer. In the world of science instead of freelancing, the variables that affect pH are simple: the concentration of hydrogen ions, which is a function of the chemistry of the solvent (if any) and the chemistry of the solute(s). Temperature and any buffering agents present also act as controls on pH. Tribe didn't say that, instead harvesting a bunch of disconnected factoids. That's Dumbass of the Day-level work.

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