Q.1 Calculate the extent of hydrolysis of 0.005M K2CrO4.If K2=5*10^-7 for H2CrO4.(It is essentially strong for first ionisation).
To calculate the extent of hydrolysis of K2CrO4, we need to determine the concentration of HCrO4- ions formed through hydrolysis.
First, let's write the equation for the hydrolysis of K2CrO4:
K2CrO4 + H2O ↔ 2K+ + HCrO4-
The equilibrium constant for this reaction is given by:
K = ( [K+]^2 * [HCrO4-] ) / [K2CrO4]
Given:
K2 = 5 * 10^-7
We need to find the concentration of HCrO4- ions, [HCrO4-].
Let's assume that 'x' is the extent of hydrolysis in moles/liter.
Then, the concentration of K2CrO4 after hydrolysis becomes 0.005 - 2x, as 2 moles of K2CrO4 form 2 moles of K+ ions.
According to the equation, 1 mole of HCrO4- ions is formed for every 2 moles of K2CrO4 that undergo hydrolysis. Therefore, the concentration of HCrO4- ions is 'x'.
Substituting these concentrations into the equilibrium expression:
K = ( [K+]^2 * [HCrO4-] ) / [K2CrO4]
K = ( (2x)^2 * x ) / (0.005 - 2x)
Now, substitute the value of K2:
5 * 10^-7 = ( (2x)^2 * x ) / (0.005 - 2x)
Simplifying the equation further, we get:
(1 - 400x) * (100x^2) = 5 * 10^-9
Expanding the equation:
100x^2 - 400x^3 = 5 * 10^-9
Rearranging the equation:
400x^3 - 100x^2 + 5 * 10^-9 = 0
Now, we can solve this equation to find the value of 'x', which represents the extent of hydrolysis of K2CrO4.
To calculate the extent of hydrolysis of K2CrO4, we need to use the given equilibrium constant (K2) and the initial concentration of K2CrO4.
The hydrolysis reaction of K2CrO4 can be represented as follows:
K2CrO4 + H2O ⇌ 2 KOH + H2CrO4
The equilibrium constant for this reaction (K2) is given as 5 * 10^(-7) for H2CrO4. Note that K2 is for the ionization of H2CrO4, which is considered a strong acid for the first ionization. Therefore, we can assume that most of the H2CrO4 completely ionizes.
The initial concentration of K2CrO4 is given as 0.005 M.
Now, let's assume the extent of hydrolysis to be 'x' (in moles) and calculate the concentrations at equilibrium:
[K2CrO4] = (0.005 - 2x) M (subtracting 2x as 2 moles of KOH are formed for every mole of K2CrO4 hydrolyzed)
[KOH] = 2x M
[H2CrO4] = 0.005 M (as it completely ionizes, so the concentration remains constant)
Using the equilibrium constant expression for the hydrolysis reaction:
K2 = ([KOH]^2 * [H2CrO4]) / [K2CrO4]
5 * 10^(-7) = (2x)^2 * 0.005 / (0.005 - 2x)
Simplifying the equation:
5 * 10^(-7) = 4x^2 / (0.005 - 2x)
Now, we can solve this equation to find the value of 'x', which represents the extent of hydrolysis. This can be done either manually by using numerical methods, or by using computer software that can solve equations numerically.
Alternatively, if you have access to a spreadsheet program like Microsoft Excel or Google Sheets, you can set up a table with incremental values of 'x' and calculate the corresponding values of both sides of the equation until you find a reasonable approximation for 'x' that satisfies the equation.
Please note that this calculation involves solving a quadratic equation, which may require the use of appropriate numerical methods or software to find an accurate solution.
Amother copied answer
CrO4^-2 + HOH ==> HCrO4^- + OH^-
Kh = kb = (Kw/k2) =
(HCrO4^-)(OH^-)/(CrO4^-2)
You know (CrO4^-2), Kw, and k2. (HCrO4^-) = (OH^-) = x.
Solve for x to determine (HCrO4^-), then extent hydrolysis = (HCrO4^-)/(CrO4^-2).
Check my work. Check my thinking.