Calculate the pH at the equivalence point for the titration of a solution containing 150.0 mg of ethylamine (C2H5NH2) with 0.1000 M HCl solution. The volume of the solution at the equivalence point is 250.0 mL. Kb for
ethylamine is 4.7 × 10−4.
these questions are followups of the original questin posted.
How much base much be added to make the
solution equalized?
Answer in units of mL
What is the pKa for this acid?
To calculate the pH at the equivalence point of this titration, we need to determine the concentration of the conjugate acid and conjugate base formed at the equivalence point.
First, let's calculate the number of moles of ethylamine (C2H5NH2) in 150.0 mg. We can use the formula:
moles = mass / molar mass
The molar mass of ethylamine (C2H5NH2) is:
2 * atomic mass of carbon (C) + 5 * atomic mass of hydrogen (H) + atomic mass of nitrogen (N)
= 2 * 12.01 g/mol + 5 * 1.01 g/mol + 14.01 g/mol
= 29.06 g/mol
Therefore, the number of moles of ethylamine (C2H5NH2) is:
moles = 150.0 mg / 29.06 g/mol
Next, let's calculate the volume of the HCl solution required to reach the equivalence point. Since we know the concentration of the HCl solution and the moles of ethylamine, we can use the formula:
moles = concentration * volume
Volume = moles / concentration
The concentration of the HCl solution is 0.1000 M and the moles of ethylamine is calculated in the previous step.
Now, we can calculate the volume of the HCl solution:
Volume = moles / concentration
= (moles of ethylamine) / (concentration of HCl solution)
= (moles of ethylamine) / 0.1000 M
Since the volume of the solution at the equivalence point is given as 250.0 mL, we have:
250.0 mL = (moles of ethylamine) / 0.1000 M
Now, we can solve for the moles of ethylamine:
moles of ethylamine = 0.1000 M * 250.0 mL
Next, we need to determine the moles of HCl that reacted with the ethylamine at the equivalence point. Since HCl is a strong acid, it will react completely with ethylamine in 1:1 stoichiometric ratio.
Therefore, the moles of HCl is also equal to the moles of ethylamine.
Now that we have the moles of HCl and its concentration, we can calculate the concentration of the conjugate acid, which is ethylammonium ion (C2H5NH3+).
Next, we can calculate the concentration of the conjugate base, which is chloride ion (Cl-), using the volume of the HCl solution at the equivalence point and the concentration of HCl.
Finally, we can use the Kb (base dissociation constant) of ethylamine, along with the concentrations of ethylammonium ion and the conjugate base, to calculate the pOH at the equivalence point.
pOH = -log10(concentration of ethylammonium ion / concentration of conjugate base)
The pH at the equivalence point can be obtained using the following equation:
pH = 14 - pOH
By following these step-by-step calculations, you should be able to determine the pH at the equivalence point for the given titration.