Calculate the concentration of HCO3- in an aqueous solution of 0.0885 M carbonic acid, H2CO3 (aq).
I was going to set this up as 0.0885 -x = ? Am I suppose to use the Ka value for carbonic acid?
Yes, k1 for carbonic acid.
0.0885 - x = 4.2e-7
Then I added 0.0885 to the right side and got 8.85e-2. Would this be the concentration or do I need to do another step?
You need another step.
H2CO3 --> H^+ + HCO3^-
.0885-x...x......x
k1 = (H^+)(HCO3^-)/(H2CO3)
To calculate the concentration of HCO3- in the aqueous solution of carbonic acid, you need to consider the dissociation of carbonic acid in water. Carbonic acid (H2CO3) undergoes a reversible reaction to produce hydrogen ions (H+) and bicarbonate ions (HCO3-).
The balanced equation for the dissociation of carbonic acid is:
H2CO3 (aq) ⇌ H+ (aq) + HCO3- (aq)
Since the concentration of H2CO3 is given as 0.0885 M, you can assume that the initial concentration of H+ and HCO3- is zero.
Let's assume that x M is the concentration of H+ and HCO3- formed at equilibrium. Therefore, the equilibrium concentration of H2CO3 will be (0.0885 - x) M.
Now, you need the equilibrium constant (Ka) for the dissociation reaction of carbonic acid. Ka represents the ratio of the concentration of products (H+ and HCO3-) to the concentration of the reactant (H2CO3). The Ka value for carbonic acid is approximately 4.3 × 10^-7.
The equilibrium expression for the reaction is given as:
Ka = [H+][HCO3-] / [H2CO3]
Substituting the values into the equilibrium expression:
4.3 × 10^-7 = x * x / (0.0885 - x)
Since the concentration of H+ and HCO3- are equal in this case, you can rewrite the above equation as:
4.3 × 10^-7 = x^2 / (0.0885 - x)
Now, you can solve this quadratic equation to find the value of x, which represents the concentration of H+ and HCO3- at equilibrium. Once you have the value of x, you can calculate the concentration of HCO3- by multiplying it by 2 (since 2 moles of HCO3- are formed for every 1 mole of H2CO3).
Please note that solving quadratic equations can get a bit complicated, and it's recommended to use a calculator or software that can handle algebraic calculations.