Respuesta :
Answer:
pH = 2.21
Explanation:
Hello there!
In this case, according to the reaction between NaF and HCl as the latter is added to the buffer:
[tex]NaF+HCl\rightarrow NaCl+HF[/tex]
It is possible for us to see how more HF is formed as HCl is added and therefore, the capacity of this HF/NaF-buffer is diminished as it turns acid. Therefore, it turns out feasible for us to calculate the consumed moles of NaF and the produced moles of HF due to the change in moles induced by HCl:
[tex]n_{HF}^{new}=0.300mol+0.150mol=0.450mol\\\\n_{NaF}^{new}=0.200mol-0.150mol=0.050mol[/tex]
Next, we calculate the resulting concentrations to further apply the Henderson-Hasselbach equation:
[tex][HF]=\frac{0.450mol}{1.0L} =0.450M[/tex]
[tex][NaF]=\frac{0.050mol}{1.0L} =0.050M[/tex]
Now, calculated the pKa of HF:
[tex]pKa=-log(6.8x10^{-4})=3.17[/tex]
We can proceed to the HH equation:
[tex]pH=pKa+log(\frac{[NaF]}{[HF]} )\\\\pH=3.17+log(\frac{0.05M}{0.45M} )\\\\pH=2.21[/tex]
Best regards!
pH is the measure of the hydrogen or hydronium ion concentration in an aqueous solution. The pH of the buffer made with HF and NaF is 2.21.
What is pH?
pH is the measure of the acidic or the basic content in a solution that can be given by the hydrogen or the hydroxide concentration.
The reaction can be shown as,
[tex]\rm NaF + HCl \rightarrow NaCl + HF[/tex]
New moles of HF is 0.300 + 0.150 = 0.450 moles and new moles of NaF is 0.200 - 0.150 = 0.050 moles.
The concentration is calculated by the Henderson-Hasselbach equation:
[tex]\rm [HF] = \dfrac{0.450 \;\rm mol}{1.0 \;\rm L} = 0.450 \;\rm M[/tex]
And,
[tex]\rm [NaF] = \dfrac{0.050\;\rm mol}{1.0 \;\rm L} = 0.050\;\rm M[/tex]
pKa of hydrogen fluoride is calculated as:
[tex]\rm pKa = - log (6.8 \times 10^{-4}) = 3.17[/tex]
The pH from the pKa can be calculated as:
[tex]\begin{aligned}\rm pH &=\rm pKa + log (\dfrac{[NaF]}{[HF]})\\\\&= 3.17 + \rm log (\dfrac{0.05}{0.45})\\\\&= 2.21\end{aligned}[/tex]
Therefore, the pH is 2.21.
Learn more about pH here:
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