In a solution of a weak acid and its conjugate base, which condition has to be true for pH to equal pKa?
The concentration of acid has to be greater than the concentration of base.
The concentration of acid has to be equal to the concentration of base.
An indicator has to be present that changes color at pKa.
You can reason this out.
pH = pKa + log (base)/(acid)
So if pH = pKa, then log (base)/(acid) must be zero. Set that as an equation to get log (base)/(acid) = 0
and 10^0 = ?
? must be 1; how do you get 1 out of
log(base)/(acid). The only way to obtain 1 is for (base) = (acid) which means log(base)/(acid) = log 1 = 0, then
pH = pKa.
so is it a b or c
for anyone else needing this info it is b
The correct condition for the pH to equal pKa in a solution of a weak acid and its conjugate base is: The concentration of acid must be equal to the concentration of its conjugate base.
To understand why this is the case, it's important to first understand what pH and pKa represent in this context.
pH is a measure of the acidity or basicity of a solution, specifically the concentration of hydrogen ions (H+) present. It is expressed on a logarithmic scale from 0 to 14, with pH 7 being considered neutral, pH less than 7 being acidic, and pH greater than 7 being basic.
pKa, on the other hand, is a measure of the acidity or basicity of a molecule or ion. It represents the extent to which an acid dissociates in water. A lower pKa value indicates a stronger acid, and a higher pKa value indicates a weaker acid.
When a weak acid (HA) and its conjugate base (A-) are in the same solution, they are in equilibrium and can interchange protons (H+). This equilibrium is described by the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In order for the pH to equal pKa, the log term must be zero, and this can only happen if [A-] is equal to [HA]. This means that the concentration of the acid must be equal to the concentration of its conjugate base.
To determine the actual concentrations of the acid and its conjugate base, one could perform a titration or use known initial concentrations of the components and the equilibrium constant of the acid dissociation reaction to calculate the concentrations at equilibrium.
In summary, the correct condition for the pH to equal pKa in a solution of a weak acid and conjugate base is that the concentration of the acid must be equal to the concentration of its conjugate base.