Calculate the concentration of hydronium ion of both buffer solutions at their s

Question

Calculate the concentration of hydronium ion of both buffer solutions at their starting pHs. Calculate the moles of hydronium ion present in 20.0 mL of each buffer. A change of pH by 1 unit means a change in hydronium ion concentration by a factor of 10. Calculate the number of moles of NaOH that would theoretically be needed to decrease the moles of hydronium calculated in #1 by a factor of 10 for each buffer. Are their any differences between your experimental results and the theoretical calculation. Which buffer had a higher buffering capacity? Why?

Explanation / Answer

(1)

We know that

pH=-log [H+]

[H+]=10-pH mol/lit

In 20 ml solution means 0.02 lit

Moles of [H+]=10-pH*0.02 moles

(2)

If pH increases 1

So [H+]=10-pH-1

So moles of hydronium ion decreasing by 10 factor.

So we know that pH+pOH=14

So [OH-]=10-pOH=10-14+pH+1

So [NaOH]=10-14+pH+1

Moles of NaOH increasing by 10 factor.

(3)

Buffer solution is able to retain almost constant pH when small amount of acid/base is added. Quantitative measure of this resistance to pH changes is called buffer capacity.A solution with more weak base, [A-], has a higher buffer capacity for addition of strong acid.

So if increasing pH by 1 factor then NaOH concentration increasing by 10 factor.So buffer capacity is higher.

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