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

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.

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.

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