Why is boric acid relatively harmless, but hydrochloric and sulfuric acid are very corrosive? There all acids?
by 
Tiffany
ANSWERS: 5
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Boric acid is a weak acid, so it doesn't fully dissociate in an aqueous solution. HCL, or Hydrochloric acid, is a strong acid: so it fully dissociates in aqueous solution.
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To add to the good answer from The Special One, not all acids are strong, if you look at acetic acid (aka vinegar...at low concentrations) and citric acid (found in most citrus fruit). The term acid tends to be assumed to automatically mean highly corrosive which is misleading, particularly when some very corrosive species (e.g. NaOH - caustic soda) are actually at the opposite end of the pH scale. To finish my long-winded answer, I wuld say that anything at the 'extreme end' of the pH scale will be corrosive.
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were you in Mr.Kelly's chemisty class?
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look at citric acid, you eat that stuff!
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The answers about pH are correct. But just to confuse, another way to cause corrosion is by oxidation by the anion. Nitric acid gives H+ and NO3(-) and for some metals it is the Nitrate anion which is responsible for the corrosion. If this happens you often get brown fumes of N2O4 in which the nitrogen is nominally +4 instead of +5 as it is in nitrate anion. In other words the Nitrogen is reduced. Note that H+ going to hydrogen gas is also a reduction which is why you can use redox tables to predict which metals will dissolve in acid to give H2. There is one other corrosive effect, which probably best covers the NaOH situation also. If the negative ion can complex the metal ion then corrosion is greatly enhanced. Some examples are OH-, Cl-, F-. Cars made of steel rust faster on salted roads because the Cl- ion can complex the iron cations produced by oxidation. Both OH- and F- will complex with silicon in glass causing it to dissolve to give silicate and fluorosilicate. The latter is used in etching glass. These processes do not involve a change in oxidation.
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