Posted: 2/18/2008 3:39:58 PM EDT
|
My son has a chemistry question he's working on, and my chemistry college class is 20+ years in the rearview mirror. Here is the setup. Things I know: - amount of acid in grams - vol of H2O - the molarity of the base - volume of the base What I need to figure out is the pH of the solution. Any chemistry majors out there? |
Is the acid in question a "strong acid"? Otherwise you'd need to know the disassociation constant of the acid to determine H+ concentration. If it's a strong acid (HCl, H2SO4, etc) and strong base (NaOH, KOH) you need to do the following... ------ moles of acid = weight of acid in grams/molecular weight of acid moles of base = volume of base * molarity of base moles of acid = moles of acid - moles of base concentration of acid = moles of acid/TOTAL volume (base + water) concentration of protons = concentration of acid * number of protons on acid (=1 for HCl, =2 for H2SO4) pH = -log[concentration of protons] ------- Of course if they aren't strong acids and bases, then it gets much more complicated. You'll need the Henderson-Hasselbalch equation and the pKa of the acid. More on that here. RF |
It was a strong unknown acid. Therefore he doesn't have the gfm of the acid. This was the part that was tripping us up. The base was NaOH. |
Hmmm... without the molecular weight of the acid, you can't really figure it out. Is there another piece of data? If you knew the pH of the acid solution, you could figure out the final pH. RF |
|
This is what we came up with. Do you think it will work? Givens: moles of NaOH, grams of acid, vol of acid (mL) is dissolved in, and volume of NaOH (Moles of base [equals to grams of acid] / gfm of acid) * vol in liters of base solve above for gfm Take the grams used * (1/gfm from above) = moles of acid m= moles of acid/liter of water (given) That give the hydroxide ion. pH = -log[hydroxide ion] |