Respuesta :
Explanation:
- Let lactic acid be represent as HA. And, pH is given as 2.75.
Hence, concentration of hydrogen ions will be calculated as follows.
pH = [tex]-log[H^{+}][/tex]
[tex][H^{+}] = 10^{-2.75}[/tex]
= [tex]1.78 \times 10^{-3}[/tex] M
= 0.00178 M
The reaction equation will be as follows.
[tex]HA \rightarrow H^{+} + A^{-}[/tex]
Initial: 0.025 0 0
Change: -0.00178 0.00178 0.00178
Equilibrium: 0.0232 0.00178 0.00178
Hence, calculate the value of [tex]K_{a}[/tex] as follows.
[tex]K_{a} = \frac{[H^{+}][A^{-}]}{[HA]}[/tex]
= [tex]\frac{0.00178 \times 0.00178}{0.0232}[/tex]
= [tex]1.37 \times 10^{-4}[/tex]
Therefore, value of the equilibrium constant is [tex]1.37 \times 10^{-4}[/tex] .
- Another method that we can use to determine the value of [tex]K_{a}[/tex] of any weak acid is when weak acid is titrating with a strong base then,
number of moles of acid = moles of salt formed by (acid + base)
These moles of salt are actually known as half equivalence point. So, at this point we need we need to measure the pH of solution with the help of a device called pH meter.
As we known that pH = [tex]pK_{a}[/tex]
and, [tex]K_{a} = 10^{-pK_{a}}[/tex]
