Hydrogen ions, which are protons, determine acidity. Conversely, hydroxide ions (OH-) produce basicity. If an aqueous solution contains more H+ than OH- ions it's acidic, and if it contains more OH- than H+ ions it's basic. And acid and a base neutralize each other because the H+ and OH- ions combine to form water.
The pH scale is based on the concentration of H+ ions in a solution. pH is the negative logarithm of the...
Hydrogen ions, which are protons, determine acidity. Conversely, hydroxide ions (OH-) produce basicity. If an aqueous solution contains more H+ than OH- ions it's acidic, and if it contains more OH- than H+ ions it's basic. And acid and a base neutralize each other because the H+ and OH- ions combine to form water.
The pH scale is based on the concentration of H+ ions in a solution. pH is the negative logarithm of the H+ concentration. In other words, it's the exponent but with the opposite sign. If a solution has an H+ concentration of 10^(-4), its pH is 4. If it has an H+ concentration of 10^-6, which is lower, it's pH is 6. This explains why lower pH indicates a more acidic solution. An solution with a pH of 7 is neutral because the product of H+ and OH- concentrations in a solution is always 10^(-14), so if the concentration of one is 10^(-7) the other must be the same. If the pH is above 7 the solution will be basic as the OH- concentration exceeds the H+ concentration.
Strong and concentrated acids are corrosive. They react with metals and can cause injury to skin and eyes. Weaker acids are often consumed in foods, for example vinegar and citrus juices. Acids taste sour.
In summary, using brackets to denote concentration,
[H+] > [OH-] = acid
[H+] < [OH-] = base
[H+] = [OH-] = neutral
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