If you have 500 ml of .15M Formic Acid, what is the pH of this solution? What is the

Question

If you have 500 ml of .15M Formic Acid, what is the pH of this solution? What is the

pKa? How many grams of Sodium Formate would you have to add to raise the pH to 3.85? How many grams of HCl would you have to add to lower the new pH by .2 ?

Answer 1

I'll get you started. It appears to me you've just copied the problem and haven't tried anything. Look up Ka for formic acid. pka = -log Ka.

Let HFo stand for formic acid.
Then .......................HFo ==> H^+ + Fo^-
I................................0.15.......0..........0
C................................-x.........x...........x
E...........................0.15-x........x...........x
Write the expression for Ka, substitute the E line into the Ka expresion and solve for x = (H^+), then convert to pH.

grams of HCOONa needed to raise pH to 3.85 is done with the Henderson-Hasselbalch equation. Same for grams HCl to change pH from 3.85 to 3.65.
Post your work if you get stuck.

Answer 2

To find the pH of a solution, you need to use the equilibrium expression for the ionization of formic acid (HCOOH), which is as follows:

HCOOH ⇌ H+ + HCOO-

To find the pH, we need to know the concentration of H+ ions in the solution. You mentioned that you have a 0.15 M solution of formic acid, but we need to determine the concentration of H+ ions.

Formic acid is a weak acid, and it partially dissociates in water. Its dissociation constant, represented as Ka, is related to the concentration of H+ ions and the concentration of the undissociated formic acid in the solution. The Ka expression is as follows:

Ka = [H+][HCOO-] / [HCOOH]

The pKa is the negative logarithm (base 10) of Ka:

pKa = -log(Ka)

To find the pH, we need the concentration of H+ ions, which can be calculated using the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

Where [A-] is the concentration of the conjugate base (HCOO-) and [HA] is the concentration of the acid (HCOOH).

Next, you asked for the pKa value. To determine the pKa, you can either consult a reference source or use experimental data. However, if you have the Ka value, you can calculate the pKa.

Finally, you asked how many grams of sodium formate (HCOONa) would need to be added to raise the pH to 3.85. To answer this question, we need to know the pKa value and the Henderson-Hasselbalch equation once again. By substituting the values into the equation, we can determine the required concentration of the conjugate base ([A-]). From there, we can calculate the number of moles of sodium formate needed, and finally convert it to grams using its molar mass.

Similarly, for the last question, to find the number of grams of HCl needed to lower the new pH by 0.2, we need to know the pKa value and use the Henderson-Hasselbalch equation to determine the required concentration of the conjugate base ([A-]). From there, we can calculate the number of moles of HCl needed, and convert it to grams using its molar mass.