Determine the [OH^-] of a solution that is 0.145 M in CO3^2-.
...CO3^2- + HOH ==> HCO3^- + OH^-
I..0.145..............0......0
C...=x................x......x
E.0.145-x.............x......x
Kb for CO3^2- = (Kw/k2 for H2CO3) = (x)(x)/(0.145-x)
Solve for x = (OH^-)
To determine the [OH^-] (hydroxide ion concentration) of a solution, we need to first write the balanced equation for the dissociation of the species present in the solution. In this case, the CO3^2- ion can react with water to form OH^- ions:
CO3^2- + H2O <=> HCO3^- + OH^-
The concentration of the CO3^2- ion is given as 0.145 M, but we don't have the initial concentration of OH^- to calculate the equilibrium concentration directly. However, we can use the equilibrium constant expression (Kw) for water to find the concentration of OH^-.
The equilibrium constant expression for water, Kw, is defined as:
Kw = [H+][OH^-]
At 25 degrees Celsius, the value of Kw is 1.0 x 10^-14.
Since water is neutral, the [H+] is equal to [OH^-]. Let's assume the concentration of OH^- as x. Therefore, [OH^-] = x.
Plugging in the values into the equilibrium constant expression, we get:
Kw = [H+][OH^-] = x * x = x^2
Now, we can solve for x:
1.0 x 10^-14 = x^2
Taking the square root of both sides:
x = √(1.0 x 10^-14) = 1.0 x 10^-7
So, the concentration of OH^- (i.e., [OH^-]) in the solution is 1.0 x 10^-7 M.
To determine the concentration of hydroxide ions ([OH^-]) in a solution that is 0.145 M in carbonate ions (CO3^2-), we need to consider the equilibrium reaction involving carbonate and hydroxide ions:
CO3^2- + H2O ⇌ HCO3^- + OH^-
In this reaction, one hydroxide ion is produced for every carbonate ion consumed. Therefore, the concentration of hydroxide ions is equal to the concentration of carbonate ions.
Thus, the [OH^-] in the solution is 0.145 M.