|MadSci Network: Chemistry|
Hi Amanda, It all comes down to what is the strongest acid and what is the strongest base. The stronger an acid is, the lower is its pKa value. The strongest acid has a pKa of -9 and is sulfuric acid (H2SO4). Conversely, the stronger a base is, the higher is its pKa value. The strongest base has a pKa of 49 and is a methyl ion (CH3-) Bearing in mind that... pKa = -log Ka Ka = Concentration of anion multiplied by concentration of hydronium ions divided by concentration of the acid For example, for a dilute solution of acetic acid (CH3COOH) Ka = [CH3COO-]x[H3O+]/[CH3COOH] = 1.75x10-5 pKa thus equals -log 1.75x10-5 = 4.76 Hope this helps! Mike Dan Berger adds: 1. If you're putting it in water, you don't need to worry as long as it's a strong acid or base in water. Sulfuric, hydrochloric, nitric and phosphoric acids are all "strong acids" in water, which means that they lose 100% of their protons and lower the pH accordingly. The same goes for bases. Most hydroxide bases (except so-called "ammonium hydroxide" which is a solution of ammonia in water--ammonia is a weak base!) are strong enough; you don't need to go to exotic and dangerous bases like methyl anion. 2. Given (1), the major thing for the answer to your question is to get the biggest bang per gram (or per molecule, not necessarily the same thing). For that you need the most H+ or OH- per gram or per molecule; and for THAT you need to know the structure of your acid or base. Pitfalls: phosphoric acid (H3PO4) only loses TWO (2) H+ per mole; the third H is a weak acid. Aluminum hydroxide, Al(OH)3 is strongly-enough bonded that it doesn't lose hydroxide easily at all; in fact, it's just as likely to lose H+!
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