$pH$ of buffers

Tutorial 1

    

In the following tutorial, we often abbreviate $ H_3O^+ $ by $ H^+ $ (Which is actually false, indeed, $ H^+ $ is always fully hydrated in water!)

Calculating the pH of a buffer Buffer definition: A buffer is a mixture of a weak base with its conjugated acid pH calculation: In the following calculation only the numbers of moles or molarities before dissociation or before interaction between the species present are included! $ pH $ $ = $ $ pK_a \; + \; \frac{n_{base}} {n_{acid}} $ $ pH $ $ = $ $ pK_a \; + \; \frac{c_{base}} {c_{acid}} $ where $ n $ are the numbers of moles $ c $ the molarities taking into account the dilution during mixing

Which of the following mixtures is (are) a buffer(s) ?

a) $NH_3$and $NH_4Cl$ b) $HCl$ and $NaCl$ c) $H_2O$ and $NaOH$ d) $HCOOH$ and $HCOONa$

For answers, use (possibly several times) the arrows ↑ Down! and ↓ Up! Complete please this question before moving on to the next one!