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Question: What is the pH of \( 3.1 \times {10^{ - 3}}M\,\,\,\,HCl? \)...

What is the pH of 3.1×10−3M    HCl?3.1 \times {10^{ - 3}}M\,\,\,\,HCl?

Explanation

Solution

In this question we have to find the pH of the given data. We know that the degree of alkalinity or acidity of a solution is known as its pH . “pH” is the negative algorithm of hydrogen ion concentration. Here we have been given the concentration of HClHCl solution. From the concentration of HClHCl we will calculate the concentration of hydrogen ions, then we will calculate the pH.

Complete answer:
We know that if the pH of the solution is less than 77 , then the solution has an acidic nature. If the pH of the solution is more than 77 then the solution has basic nature. If the pH of the solution is equal to 77 , then we know that the solution is neither acidic or basic, it is neutral in nature .
Here we have been given the concentration of HClHCl which is 3.1×10−3M3.1 \times {10^{ - 3}}M .
We know that HClHCl is a strong acid and dissociates completely in water.
The dissociation reaction of HClHCl is as follow:
HCl→H++Cl−HCl \xrightarrow H^+ + Cl^-
We know that the concentration of H+{H^ + } is equal to HClHCl
So we can say that the concentration of H+{H^ + } due to HClHCl is
3.1×10−3M3.1 \times {10^{ - 3}}M .
We know that pH is the negative logarithm of the hydrogen ion concentration, so we can write this as pH=−log⁡[H+]pH = - \log \left[ {{H^ + }} \right]
We will substitute 3.1×10−3M3.1 \times {10^{ - 3}}M for the hydrogen ion concentration, Thus we have:
pH=−log⁡(  3.1×10−3M)pH = - \log \left( {\;3.1 \times {{10}^{ - 3}}M} \right)
We will now simplify this:
⇒pH=−log⁡(  3110×11000M)\Rightarrow pH = - \log \left( {\;\dfrac{{31}}{{10}} \times \dfrac{1}{{1000}}M} \right)
⇒pH=−log⁡(  0.0031)\Rightarrow pH = - \log \left( {\;0.0031} \right)
Now we will substitute the value of given logarithm expression and we have:
⇒pH=−(−2.5086)\Rightarrow pH = - ( - 2.5086)
⇒pH=+2.5086\Rightarrow pH = + 2.5086
Hence the required pH is 2.512.51 .

Note:
We should note that as we have calculated above the pH of the hydrogen ion is less than 77 , so we can say that the 3.1×10−3M3.1 \times {10^{ - 3}}M solution of HClHCl is acidic in nature. We must always remember that as concentration increases with temperature, the pH always changes. With the increase in temperature the pH decreases, however this does not mean that the water becomes acidic at higher temperature.