Hi Paul you asked for it
1) What does the abbreviation pH stand for?
2) How much more acidic is water with pH of 4.5 than water with a PH of 5.5?
See? We don't understand much about pH after all. The answers are "per Hydrion" and "ten times" respectively. Allow me to explain.
Hydrogen in its cation state is known as "hydrion". The pH scale is a logarithmic scale and can also be referred to as a "molar concentration" of hydrion ions. Now you are scratching your head and saying "Huh"? A "mole" in chemical terms is a set quantity of molecules, that quantity being referred to as Avagadro's number. Consider the number 602 with twenty-one zero's trailing it. That's a mole. A "molar concentration" is the number of moles of hydrion ions in a liter of water. Since it works out to be less than one, we can express it as a fraction (groans from the mathematically challenged). When you see a pH value of "X", it really means the molar concentration is 1/10x moles of hydrion for each liter of water. So, if you have a pH of 5.0 that means that for each mole of stuff in the sample you have 1/105, or 0.00001 moles of hydrion. Doesn't sound like a lot, but remember a mole is a really big number. You would think that it contains a lot of hydrion, but it doesn't. One mole or 602,000,000,000,000,000,000,000 ions of hydrion works out to weigh only one gram, That means a liter of water at a pH of 5.0 has only ten micrograms or ten millionths of a gram of hydrion ions. A pH of 6.0 indicates a concentration of 0.000001, or one millionth of a gram.
What about a pH of 5.1 you ask? Or 5.2, 5.3, etc? Remember this is a logarithmic scale so it kind of curves its way along, with the difference between 5.0 and 5.1 being greater than the difference between 5.1 and 5.2, and so on. Suffice it to say that it is somewhere in between and the closer it gets to6.0, the fewer it has.
At this point you need to introduce a scientific convention. Scientific conventions are things scientists all agree on so they can communicate better (and I' " bet you thought it was a bunch of nerds with lab coats and pocket protectors taking over a hotel). When a Hydrogen atom is in the hydrion state it can be shown as "H+". When it has an extra ion and therefore is negatively charged it is written as "H-" and is called Hydride. The chemical symbol for Calcium is Ca and when it is in ionic form it will be short two electrons. This will cause it to have a double positive charge and will be written as CA++. Nifty huh?
Maybe here it would be a good idea todiscuss "mass solutions.. as opposed to "molar solutions". (and not he ones I sell) While molar solutions are based on the number of molecules of something in one litre of water, a mass solution measures the weight of the substance dissolved in a liter of water. It is expressed as mg/1 (milligrams per liter) or mmg (micrograms per liter). We will need this definition later so stick it into the back of your head for future reference.
Now back to Ph water below a pH of less than 7.0 is "acidic" and above 7.0 is considered ..b,ase". If you were to distill water to an absolute purity and keep it from dissolving anything - even air, it would have a pH of 7.0. Why? Because water is an ionic compound. As such its chemical bond is not as strong as it would appear.
I'll leave it there for now
Best regards Nick
