Quadratic Formula

Moderators: Chem_Mod, Chem_Admin

Kassidy Tran 1E
Posts: 77
Joined: Fri Sep 28, 2018 12:15 am

Quadratic Formula

Postby Kassidy Tran 1E » Mon Jan 21, 2019 7:30 pm

I'm a bit confused on when we need to apply the quadratic formula and use the ICE table. How can we tell when to use this?

Matthew Choi 2H
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

Re: Quadratic Formula

Postby Matthew Choi 2H » Mon Jan 21, 2019 7:56 pm

Typically, you use an ICE table when the question asks for the equilibrium concentrations of a reaction and they give you the initial concentrations. Then when you construct your ICE table, you will fill in the blanks for the initial concentrations but use "x" for the change in concentration from initial to equilibrium. In order to find out what "x" is, you write the Ka/Kb expression with the equilibrium concentrations of the products over the equilibrium concentrations of the reactants. When you simplify the expression, you might end up with a quadratic equation in which case you would use the quadratic formula to solve for "x".

Hedi Zappacosta 1E
Posts: 66
Joined: Fri Sep 28, 2018 12:27 am

Re: Quadratic Formula

Postby Hedi Zappacosta 1E » Mon Jan 21, 2019 8:55 pm

If you are dealing with a very weak acid or base, then you can assume that x is negligible and eliminate the x from the denominator of your Ka equations, leaving you with x^2/the original concentration of the acid or base. To check if it was correct to assume that x was negligible, check the percent ionization, and if it is less than 5%, then it was okay to assume negligibility.


Return to “Equilibrium Constants & Calculating Concentrations”

Who is online

Users browsing this forum: No registered users and 1 guest