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20 mL of an approximately 10% aqueous solution of ethylamine, CH3CH2NH2, is titrated with 0.3000 M aqueous HCl. Which indicator would be most suitable for this titration? The pKa of CH3CH2NH3+ is 10.75.
Answer:
Bromocresol green, color change from pH = 4.0 to 5.6
Explanation:
The equation for the reaction is as follows:
+
⇄
Given that concentration of = 10%
i.e 10 g of in 100 ml solution
molar mass = 45.08 g/mol
number of moles =
= 0.222 mol
Molarity of = 0.222 ×
= 2.22 M
However, number of moles of in 20 mL can be determined as:
number of moles of = 20 mL × 2.22 M
=
Concentration of =
= 2.22 M
Similarly, The pKa Value of is given as 10.75
pKb value will be: 14 - pKa
= 14 - 10.75
= 3.25
Finally, the pH value at equivalence point is:
pH=
pH =
pH = 5.21
∴
The indicator that is best fit for the given titration is Bromocresol Green Color change from pH between 4.0 to 5.6.