#1 a buffer is prepare from hypochlorous acid (HCIO) and sodium hypochlorite (NaCIO). It contains 0.075 mol of the acid and 0.055 mol of the base in 250.mL of aqueous solution. Calculate the pH of this buffer. (Ka=3.5x10-8)

0.025 moles HnO3 is added to the buffer from problem #1

what component of the buffer will it react with? what is the balance equation for the reaction.

use a table to determine the moles of all species after the reaction takes place

calculate the pH of the new solution. Is this a good buffer or not? compare it to the calculated pH from #1

 

• pH initial = 7.33
• NaClO will react with HNO₃, according to the reaction HNO₃ + NaClO → NaNO₃ + HClO
• pH final = 6.94

Step-by-step explanation

For the preparation of your buffer, you mixed 0.075 mol of HClO and 0.055 mol of NaClO. Your acid component is HClO while your base component is NaClO. To solve for the pH, we simply use the Henderson-Hasselbalch Equation for buffers, which goes

pH = pK_a + log?MolesofAcidMolesofBase??

pK_a is simply -logK_a, so pK_a = -log(3.5 x 10^-8) = 7.46

Thus, pH = 7.46 + log?0.075mol0.055mol??

pH = 7.33

For the second part, you added 0.025 mol HNO₃, a strong acid. Being an acid, it will of course react with your basic component, NaClO. The balanced equation is HNO₃ + NaClO → NaNO₃ + HClO.

The balanced equation dictates that your NaClO will react (decrease) the same amount of HNO₃ added, and the HClO will increase the same amount of HNO₃ added. The table summarizes what will happen in the reaction:

Thus, Final Moles Base = 0.03 mol and Final Moles Acid = 0.10 mol, and pH = 7.46 + log?0.10mol0.03mol??

pH = 6.94

ΔpH = 6.94 - 7.33 = -0.39

Your pH dropped by only 0.39 units, which is not bad, considering that HNO₃ is a strong acid. Thus, your buffer is okay.

Please see the attached file for the complete solution