Using an ICE Table with Concentrations Example

often carried out for weak acid titrations

Find the concentration of A- for the generic acid dissociation reaction:

HA(aq)+H2O(l)⇌A−(aq)+H3O(aq)

with [HA(aq)] initial=0.150M and Ka=1.6×10−2

1. Fill in given concentrations:
Reaction:HAA-H3O+I0.150 M0.000 M0.000 MC???E???
2. Calculate the change concentrations by using a variable 'x'Reaction:HAA-H3O+I0.150 M0.000 M0.000 MC-x M+x M
+x M
E???

The change in concentration is unknown, so the variable x is used to denote the change. x is the same for both products and reactants because equal stoichiometric amounts of A- and H3O+ are generated when HA dissociates in water

3. Calculate the concentrations at equilibrium

Reaction:HAA-H3O+I0.150 M0.000 M0.000 MC-x M+x M+x ME0.150 - x Mx Mx M

4. Use the ICE table to calculate concentrations with Ka

The expression for Ka is written by dividing the concentrations of the products by the concentrations of the reactants. Plugging in the values at equilibrium into the equation for Ka gives the following:

Ka=x20.150−x=1.6×10−2

To find the concentration x, rearrange this equation to its quadratic form, and then use the quadratic formula to find x:

(1.6×10−2)(0.150−x)x2+(1.6×10−2)x−(0.150)(1.6×10−2)==x20

solve for x and eliminate the negative version of x

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Notiz am Chemistry Final Review, erstellt von pierox38 am 17/06/2014.