Question

A nitric acid solution, pH=2.7, results from NO_x removal from a stack gas. Neglect ionic strength effects and the temperature is 25^oC. How much Na₂CO_{3 must be added to neutralize this solution prior to discharge? (the final pH=8.3. Assume that no weak acids are present in the scrubber water.) What is the buffer intensity of the final solution?}

I figured out the first question already. But I have no idea how to calculate the buffer intensity.............

Answer 1

In this case, we have the following equations:

pH = -log[H⁺]

We have the pH of both solutions, so solving for H⁺:

[H⁺] = antlog(-pH) = 10^-pH

To know the quantity to be added to neutralize this solution, and assuming there's no weak acids presents, then just calculating the quantity of H⁺ to be neutralized, we know how much is needed to neutralize the solution so:

[H⁺] = [H⁺]₁ - [H⁺]₂

[H⁺]₁ = antlog(-2.7) = 1.9953x10^-3 M

[H⁺]₂ = antlog(-8.3) = 5.0119x10^-9 M

So the final would be:

[H⁺] = 1.9953x10^-3 - 5.0119x10^-9 =1.9953x10^-3 M

Then, the relation between Na₂CO₃ and HNO₃ is 2:1 so:

[Na₂CO₃] =1.9953x10^-3 M / 2 = 9.9765x10^-4 M

Now a buffer is prepared by mixing two solutions, so, adding this solution to HNO₃ we'll got a buffer and the intensity:

[B] = [HNO₃] + [Na₂CO₃]

[B] = 1.9953x10^-3 + 9.9765x10^-4 M

[B] = 2.993x10^-3 M

Hope this helps