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Asked by anon-217186 to Savannah, Philippe, Lucy, Joanna, Harrison, Edoardo on 12 Jun 2019.
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Edoardo Vescovi answered on 12 Jun 2019: last edited 13 Jun 2019 12:09 am
pH measures the concentration of hydrogen ions (in symbol, H+) in water that contains chemicals.
One step back. Hydrogen atoms (H) have a nucleus made of 1 proton and have 1 electron orbiting around it. They are neutral because the proton (positive) charge compensates that (negative) of the electron. Coming to H+, the “+” means that one electron is gone, leaving only a proton. H+ is an “ion” because it has net electric charge.
Next step: the higher the number of H+ is, the lower the pH is and vice versa. Since chemistry (and science) is more than words, we say that pH is minus the logarithm of their number. Don’t worry what logarithm is and how the number of H+ is measured; keep an eye on the minus instead. It says that pH decreases when the number increases, just as said in words. By the way, the number is measured in “moles”, but nothing to do with the animal!
Final step is to remind that an acid tends to create H+, the opposite goes for alkali, whereas water has somehow a neutral tendency. So acids have lower pH. This should answer your question in simple words.
You find a nice pH scale and the math definition of pH in https://en.wikipedia.org/wiki/PH for example.
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Lucy Budge answered on 12 Jun 2019:
I think Edoardo has got this answer covered!
In two sentences: pH is a measure of how acidic something is – with a lower number being more acidic than a higher one. By definition alkalis are the opposite of acids (if you mix them together you get something neutral) and so alkalis have a high pH.
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Savannah Clawson answered on 12 Jun 2019:
I think everyone else already have this answer covered – basically a pH level is just a measurement of how acidic something is. The pH scale goes from 1 to 14. Anything with a pH level below 7 is an acid and anything with a pH level about 7 is an alkali (water is neutral with a pH of 7). Acids produce molecules called ions that have a positive charge when they are added to water, whereas alkalis produce ions with a negative charge.
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Philippe Gambron answered on 14 Jun 2019:
It’s the definition of the pH. An acid will have a low pH and an alkali a high one.
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