When 50.0 mL of 0.050 M formic acid, HCHO2, is
titrated with 0.050 M sodium hydroxide, what is the pH
at the equivalence point?
NaOH + HCOOH ==> HCOONa + H2O
The pH at the equivalence point is determined by the hydrolysis of the salt, in this case sodium formate.
Write the hydrolysis equation and set up an ICE chart, solve for OH^- and converft to pH. Kb for the formate ion is Kb = Kw/Ka for formic acid.
To determine the pH at the equivalence point of the titration, we need to understand the reaction between formic acid (HCHO2) and sodium hydroxide (NaOH).
The balanced chemical equation for the reaction is:
HCHO2 + NaOH → HCOONa + H2O
In this reaction, formic acid reacts with sodium hydroxide to produce sodium formate (HCOONa) and water (H2O).
At the equivalence point, the moles of formic acid are stoichiometrically equivalent to the moles of sodium hydroxide added. This means that all the formic acid has reacted to form sodium formate. The resulting solution will be a sodium formate solution.
To calculate the pH, we need to consider the dissociation of sodium formate in water. Sodium formate is the salt of a weak acid (formic acid) and a strong base (sodium hydroxide). When a salt dissolves in water, it can undergo hydrolysis, leading to the formation of a weak acid or base.
In the case of sodium formate, it undergoes hydrolysis to form formic acid (a weak acid) and hydroxide ions (OH-):
HCOONa + H2O → HCHO2 + NaOH
The hydroxide ions (OH-) from the hydrolysis will increase the pH of the solution.
To determine the pH at the equivalence point, we need to find the concentration of hydroxide ions (OH-) in the solution. Since we started with equal concentrations of formic acid (HCHO2) and sodium hydroxide (NaOH), at the equivalence point, half of the formic acid is neutralized and converted into sodium formate.
Therefore, the concentration of sodium formate at the equivalence point is 0.050 M / 2 = 0.025 M.
When a salt like sodium formate dissociates in water, it produces equal amounts of hydroxide (OH-) and formate (HCOO-) ions. So, the concentration of hydroxide ions in the solution is also 0.025 M.
Now, to find the pOH, we can use the formula:
pOH = -log[OH-]
pOH = -log(0.025) ≈ 1.60
To calculate the pH, we can use the equation:
pH + pOH = 14
pH + 1.60 = 14
pH ≈ 12.4
Hence, the pH at the equivalence point is approximately 12.4.
To determine the pH at the equivalence point of the titration, we need to consider the reaction between formic acid (HCHO2) and sodium hydroxide (NaOH).
The balanced chemical equation for the reaction is as follows:
HCHO2 + NaOH → HCOONa + H2O
At the equivalence point, the moles of acid will be equal to the moles of base. In this case, the volume of sodium hydroxide required to reach the equivalence point is not provided, so we will calculate the pH at the equivalence point assuming equal volumes of acid and base are used.
Step 1: Calculate the moles of formic acid (HCHO2):
Moles of HCHO2 = Volume of HCHO2 solution (L) × Molarity of HCHO2 (mol/L)
= 0.050 L × 0.050 mol/L
= 0.0025 mol
Step 2: Calculate the moles of sodium hydroxide (NaOH) required to react with 0.0025 mol of formic acid:
From the balanced equation, the stoichiometric ratio between HCHO2 and NaOH is 1:1. Therefore, the moles of NaOH required = 0.0025 mol.
Step 3: Calculate the volume of sodium hydroxide solution needed:
Volume of NaOH solution (L) = Moles of NaOH (mol) / Molarity of NaOH (mol/L)
= 0.0025 mol / 0.050 mol/L
= 0.050 L or 50.0 mL
Since equal volumes of acid and base are used at the equivalence point, the final volume of the solution will be 100.0 mL.
Step 4: Determine the concentration of the resulting salt (sodium formate, HCOONa):
Since equal moles of acid and base react at the equivalence point, the concentration of the salt formed after the reaction will be:
Concentration of HCOONa = Moles of HCOONa / Volume of solution (L)
= 0.0025 mol / 0.100 L
= 0.025 M
Step 5: Calculate the pH of the resulting sodium formate (HCOONa) solution:
Sodium formate (HCOONa) is a salt of a strong base (NaOH) and a weak acid (HCHO2). As a result, the pH of its solution will be basic.
To find the pH, we can use the formula:
pH = 14 - pOH
Since the solution is basic, we need to find the pOH using the concentration of sodium formate:
pOH = -log10[NaOH]
= -log10(0.025)
= 1.60
Then, we can find the pH using the pOH:
pH = 14 - pOH
= 14 - 1.60
= 12.40
Therefore, the pH at the equivalence point is approximately 12.40.