Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
Chemistry question? Simple stoicheometry?
2HCl + caco3 -> h2co3 + cacl2
h2co3 -> h2o + co2
I used 50mL of HCl, and 0.1g of CaCO3
the co2 produced from the previous reaction, which is 24mL and 0.001 moles (found out with stoicheometry), is dissolved in 25mL of h2o. Here is the equation:
co2 + h2o <-> h2co3 <-> (h+) + hco3
my question is: how do you find the pH (concentration of (H+)) using stoicheometry?
help would be awesome! thanks!
1 Answer
- Robert DLv 78 years agoFavorite Answer
In order to do this you must ASSUME that all of the CO2 produced is dissolved in the water. This is not a normal behavior for CO2(g), but for the calculation we must use this assumption.
CO2(g) --> CO2(aq) We are assuming that this happens 100%. This is really an equilibrium, but I am writing it as a reaction (or process).
[CO2] = 0.001 mol/0.024 L = 0.042 M
Equilibrium: CO2(aq) + H2O(l) <=> H^+(aq) + HCO3^-(aq)
Ka = [H^+][HCO3^-]/[CO2] = 4.5 x 10^-7 (see link below)
Let x = [H^+] = [HCO3^-] and [CO2] = 0.042 - x (First assume that x is negligible)
x^2/(0.042) = 4.5 x 10^-7
x^2 = (4.5 x 10^-7)(0.042) = 1.875 x 10^-8
x = sq. root(1.875 x 10^-8) = 1.40 x 10^-4 M = 0.000140 M
error of assumption: [(0.000140)/(0.042)] x 100% = 0.3 % This is an acceptible error. The assumption is valid.
pH = -log[H^+] = -log(1.40 x 10^-4) = 3.85
Hope this is helpful to you. JIL HIR
