Methanoic acid HCO2H(aq) also known as formic acid, is partly responsible for the characterisitic itchy rash produced by the leaves of the stinging nettle plant. Calculate the pH of 0.150 mol/L methanoic acid. The Ka for methanoic acid is 1.8 x 10^-4.

Follow the generic procedure I showed you for lactic acid.

To calculate the pH of a solution of a weak acid like methanoic acid (HCO2H), we need to use the acid dissociation constant (Ka) and the initial concentration of the acid.

Step 1: Write down the balanced equation for the dissociation of methanoic acid in water:
HCO2H(aq) ⇌ H+(aq) + HCO2-(aq)

Step 2: Write the expression for the acid dissociation constant (Ka):
Ka = [H+(aq)][HCO2-(aq)] / [HCO2H(aq)]

Step 3: Since methanoic acid is a weak acid, we assume that the concentration of H+ that is formed in the dissociation is x.

Ka = x^2 / (0.150 - x)

Note: The concentration of HCO2-(aq) will also be x since it is stoichiometrically equivalent to H+.

Step 4: Substitute the given value for Ka into the equation:
1.8 x 10^-4 = x^2 / (0.150 - x)

Step 5: Solve the quadratic equation to find the value of x. Rearrange the equation to the standard quadratic form:
x^2 + (1.8 x 10^-4)x - (1.8 x 10^-4)(0.150) = 0

Step 6: Solve the quadratic equation using the quadratic formula:
x = [-b ± √(b^2 - 4ac)] / (2a)

For this equation, a = 1, b = 1.8 x 10^-4, and c = -1.8 x 10^-4(0.150).

Step 7: Calculate x using the quadratic formula, and choose the appropriate value of x (the smaller positive solution) to determine the concentration of H+.

Step 8: Once you have the concentration of H+, calculate the pH using the formula:
pH = -log[H+]

That's the step-by-step process for calculating the pH of a solution of methanoic acid!