A solution of the weak acid HA was titrated with 0.100 M NaOH. the pH measured when vb=ve was 4.62 mL was 4.62 mL. Calculate the Ka of weak acid. (vb= added base volume, ve= equivalence point reading)
mols NaOH = M x L = ?
pH = 4.62 mL?????
Please rephrase the question of supply additional information.
To calculate the Ka of the weak acid, we need to follow these steps:
Step 1: Find the moles of NaOH used.
Since the volume of NaOH used (vb) is given as 4.62 mL and the concentration of NaOH is given as 0.100 M, we can calculate the moles of NaOH using the formula:
moles of NaOH = volume (in liters) × concentration (in mol/L)
= (4.62 mL / 1000 mL/L) × 0.100 mol/L
Step 2: Determine the moles of the weak acid.
Since the balanced equation for the reaction between the weak acid (HA) and NaOH is 1:1, the moles of the weak acid will be the same as the moles of NaOH.
Step 3: Calculate the molarity of the weak acid.
The volume of the weak acid used (vb) and the volume of NaOH used (vb) are equal at the equivalence point. Therefore, the moles of the weak acid (HA) will be the same as the moles of NaOH. Since the volume of the weak acid is not given in the question, we'll assume it's in excess, so the initial moles of the weak acid and remaining moles of the weak acid will be equal.
Therefore, we can calculate the initial moles of the weak acid using the formula:
moles of HA = moles of NaOH
= (4.62 mL / 1000 mL/L) × 0.100 mol/L
Step 4: Calculate the initial molarity (concentration) of the weak acid.
The initial molarity (M) can be calculated using the formula:
Molarity (M) = moles / volume (in liters)
Therefore, the initial molarity of the weak acid (HA) can be calculated using the formula:
Molarity of HA = moles of HA / volume (in liters)
Step 5: Calculate the concentration of H+ ions.
Since the pH of the solution is given as 4.62 mL, we know that the concentration of H+ ions is 10^(-pH) or 10^(-4.62).
Step 6: Calculate the concentration of the weak acid (HA) dissociated.
At the equivalence point, all of the weak acid (HA) is converted to its conjugate base (A-).
Since the reaction is 1:1, the concentration of the dissociated acid (A-) will be the same as the concentration of the added base (NaOH).
Therefore, the concentration of the weak acid dissociated (A-) is equal to the molarity of NaOH: 0.100 M.
Step 7: Calculate the concentration of the weak acid (HA) undissociated.
The concentration of the weak acid (HA) undissociated (HA) is equal to the initial concentration minus the concentration of the weak acid dissociated (A-).
Therefore,
Concentration of HA undissociated (HA) = Initial concentration - Concentration of A-
Step 8: Calculate the Ka of the weak acid.
The Ka value is the ratio of the concentration of the products (H+ and A-) to the concentration of the reactants (HA).
The equation for the dissociation of a weak acid (HA) can be represented as HA ⇌ H+ + A-
Therefore,
Ka = [H+] * [A-] / [HA]
By substituting the values we obtained from the previous steps into this equation, we can calculate the Ka value of the weak acid.