Question

What's the pH of a solution composed of 0.2 moles of NH3 and 0.15 moles of nh4cl​

Answer 1

Answer:

$pH=4.63$

Explanation:

Hello!

In this case, since the ionization of ammonia, which is a weak base, is written as:

$NH_3+H_2O\rightleftharpoons NH_4^++OH^-$

We can see that the ammonium ion is the conjugate acid whereas the hydroxide ions the conjugate base; that is why we use the Henderson-Hasselbach equation to compute the pH, given the pKb of ammonia 4.75:

$pH=pKb+log(\frac{[conj\ acid]}{[base]} )$

In such a way, for the given moles of ammonia, base, and those of ammonium chloride, conjugate acid form, we obtain:

$pH=4.75+log(\frac{0.15}{0.2} )\\\\pH=4.63$

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