Question

Calculate the ratio of ch3nh2 to ch3nh3cl required to create a buffer with ph = 10.28. express your answer using two significant figures.

Answer 1

Hello!

The chemical reaction for the ionization of CH₃NH₂ is the following:

CH₃NH₂ + H₂O ⇄ CH₃NH₃⁺ + OH⁻ pKb=3,30

$pKa=14-pKb=14-3,30=10,70$

Now we apply the Henderson-Hasselbach equation and clear for the ratio of CH₃NH₂ to CH₃NH₃Cl:

$pH=pKa+log( \frac{[CH_3NH_2]}{[CH_3NH_3Cl]} ) \\ \\\frac{[CH_3NH_2]}{[CH_3NH_3Cl]}= 10^{(pH-pKa)}= 10^{(10,28-10,70)}=0,38$

So, the ratio of CH₃NH₂ to CH₃NH₃Cl is 0,38

Have a nice day!