Ascorbic acid, H2C6H6O6, is a diprotic acide with a K1= 7.9 E-5 and a K2=1.6E-12. In a .005 M aq solution of ascorbic acid which of the following species is present in the lowest concentration.
1. H2O
2. H3O
3. H2C6H6O6
4. HC6H6O6
5. C6H6O6
You didn't put charges on what you wrote. The way you work this problem is to write the ionization of the two hydrogens and the k1 and k2 expressions. Then some reasoning ability to see which one is the least. k1 and k2 are given so logic will tell you.
To determine which species is present in the lowest concentration in a .005 M aqueous solution of ascorbic acid, you need to compare the dissociation of ascorbic acid through its two dissociation constants, K1 and K2.
Ascorbic acid, H2C6H6O6, is a diprotic acid, meaning it can donate two protons. It first donates one proton to form the first dissociation product, HC6H6O6-, and then donates the second proton to form the second dissociation product, C6H6O6-.
Let's write down the dissociation reactions and their respective equilibrium expressions:
1. H2C6H6O6 ⇌ HC6H6O6- + H+
Equilibrium expression: K1 = [HC6H6O6-][H+] / [H2C6H6O6]
2. HC6H6O6- ⇌ C6H6O6- + H+
Equilibrium expression: K2 = [C6H6O6-][H+] / [HC6H6O6-]
In an aqueous solution of ascorbic acid with an initial concentration of 0.005 M, the concentration of H2C6H6O6 can be assumed to remain nearly constant as it does not significantly dissociate.
To determine which species is present in the lowest concentration, we need to compare the concentrations of the dissociation products, HC6H6O6-, and C6H6O6-.
At equilibrium, the concentration of H+ can be obtained by rearranging the equilibrium expression for the first dissociation:
[H+] = (K1 * [HC6H6O6-]) / [H2C6H6O6]
Similarly, the concentration of H+ in the second dissociation can be obtained using the equilibrium expression for the second dissociation:
[H+] = (K2 * [C6H6O6-]) / [HC6H6O6-]
Given that the initial concentration of H2C6H6O6 is 0.005 M, you can substitute this value along with the known values of K1 and K2 into the above equations to calculate the concentrations of HC6H6O6- and C6H6O6-.
Now compare the concentrations of HC6H6O6- and C6H6O6-. The species with the lower concentration is present in the lowest concentration in the solution. Based on this comparison, you can determine which of the given species (H2O, H3O, HC6H6O6, or C6H6O6) is present in the lowest concentration.