Calculate the pH of 0.0115M acetic acid solution at 25 degrees celcius with Ka=1.75*10^-5
Note the correct spelling of celsius.
CH3COOH lets call HAc.
.............HAc ==> H^+ + Ac^-
initial....0.0115.....0......0
change.......-x.......x......x
equil.....0.0115-x....x......x
Ka = (H^+)(Ac^-)/(HAc)
Substitute and solve for x then convert to pH.
Thanx a lot GOD BLESS YOU
To calculate the pH of a solution of acetic acid, we need to use the equilibrium expression for the dissociation of acetic acid in water.
The equation for the dissociation of acetic acid is as follows:
CH3COOH + H2O ⇌ CH3COO- + H3O+
The equilibrium constant for this reaction is known as the acid dissociation constant (Ka). The Ka value for acetic acid is given as 1.75 * 10^-5.
To solve the problem, we need to set up an ICE (Initial, Change, Equilibrium) table and use the given Ka value to calculate the concentration of hydronium ions (H3O+).
1. Set up the ICE table:
- We start with an initial concentration of acetic acid (CH3COOH) of 0.0115 M.
- Since acetic acid is a weak acid, we assume that it will only partially dissociate in water.
- We can let 'x' represent the concentration of hydronium ions (H3O+).
- The equilibrium concentration of acetic acid (CH3COOH) will then be (0.0115 - x) M, while the concentration of acetate ions (CH3COO-) will also be (0.0115 - x) M.
2. Write the equilibrium expression:
Ka = [CH3COO-][H3O+] / [CH3COOH]
3. Substitute the values into the equation:
1.75 * 10^-5 = (0.0115 - x)(x) / (0.0115 - x)
4. Simplify the equation:
(0.0115 - x)(x) = (1.75 * 10^-5)(0.0115 - x)
5. Solve the equation:
Distribute and rearrange the equation to obtain a quadratic equation:
x^2 - 0.0115x + 1.75 * 10^-5 * x - 1.75 * 10^-5 * 0.0115 = 0
Solve the quadratic equation using either factoring, completing the square, or the quadratic formula. In this case, we can use the quadratic formula:
x = (-b ± √(b^2 - 4ac)) / 2a
Plugging in the values:
x = (-(-0.0115) ± √((-0.0115)^2 - 4(1)(-1.75 * 10^-5 * 0.0115))) / (2 * 1)
6. Calculate the values of x (concentration of H3O+):
By solving the quadratic equation, we find two values for x: x1 and x2.
In this case, one value of x will be negligible compared to the other (since acetic acid is a weak acid), so we can ignore x2.
Therefore, x = x1.
7. Calculate the pH:
pH is defined as the negative logarithm of the concentration of hydronium ions (H3O+):
pH = -log[H3O+]
Calculate [H3O+] by plugging in the value of x into the equation.
That's how you calculate the pH of a solution of acetic acid using its Ka value. Remember to round the final pH value to the appropriate number of significant figures, based on the given data.