melody2k6 wrote:starpug wrote:frogzorz wrote:Oops. My bad. I thought it had two sulfur molecules. I hate my partner!!
A weak acid? We tested for a pH of 1 or 2.
It's a common mistake
Also the term "weak acid" doesn't mean it can't have a ph of 1 or 2. pH is a measure of H+ ion concentration, so a saturated solution of say citric acid (what makes lemons so sour) can have a pH as low as or lower then a dilute solution of HCl. What makes HCl and other strong acids strong is that they completely dissociate in water so if you were to add the same number of moles of HCl and citric acid to water, the HCl would have the higher pH. The HCl would donate more H+ ions to the solution then the citric acid (making more Hydronium Ions, but the difference between H+ and H30+ is irrelvant to what I'm saying.) which makes the pH lower (they're inversely proportional since pH is the -log[H+]). Even among weak acids, some are stronger then others because some dissociate better then others. Also, pH paper has a history of being unreliable, so it's possible that was a faulty reading.
Ferric Acid's formula H2FeO4, I can't seem to find it's dissociation constant so I don't know how strong of a weak acid it is.
I have always thought a weak acid meant an acid with a pH close to neutral. When my partner and I tested the pH of Ferric Acid (or whatever it is) we got a pH of 4. Would that be considered a weak acid?
Let me say this, pH does not tell you whether it is strong or weak acid, unless you know the concentration of the solute in the solution as in that case the H+ concentration you get from the pH (if the pH was 4 the H+ concentration would be .0001 mol/L) matches the total concentration of the solute in the solution you have a strong acid. If it were less then the total concentration it would be weak.
I don't think they gave you enough data to do that, so it's much easier to memorize the strong acids
HCl - Hydrochloric
HI - Hydroiodic
HBr - Hydrobromic
H2SO4 - Sulfuric
HClO4 - Perchloric
HClO3 - Chloric
HNO3 - Nitric
Anything else is a weak acid