Question

the molarity of nitrous acid at which its pH becomes 2​

Answer 1

Nitric acid, HNO2 is a weak acid with Ka= 4.5 x 10-4. It dissociates according to: HNO2 (aq) <--> H+ (aq) + NO2- (aq) a.) What is the pH ...

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Answer 2

Answer: The molarity of nitrous acid at pH = 2 is 0.222 M

Explanation:

To calculate the pH of the solution, we use the equation:

$pH=-\log[H^+]$

We are given:

pH = 2

Putting values in above equation, we get:

$2=-\log[H^+]$

$[H^+]=10^{-2}$

The chemical equation for the dissociation of nitrous acid follows:

$HNO_2(aq.)\rightarrow H^+(aq.)+NO_2^-(aq.)$

We know that:

$K_a(HNO_2)=4.5\times 10^{-4}$

The expression of $K_a$ for above reaction is:

$K_a=\frac{[H^+][NO_2^-]}{[HNO_2]}$

Taking concentration of $H^+\text{ and }NO_2^-$ as equal. Putting values in above equation, we get:

$4.5\times 10^{-4}=\frac{10^{-2}\times 10^{-2}}{[HNO_2]}$

$[HNO_2]=\frac{10^{-4}}{4.5\times 10^{-4}}=0.222M$

Hence, the molarity of nitrous acid at pH = 2 is 0.222 M