What is the expected pH of a 0.0055 M solution of HCl. Write your answer to 3 decimals.
The correct answer and explanation is:
Answer:
The expected pH of a 0.0055 M solution of HCl is 2.260.
Explanation:
Hydrochloric acid (HCl) is a strong acid, which means it completely dissociates in aqueous solution: HCl→H++Cl−\text{HCl} \rightarrow \text{H}^+ + \text{Cl}^-
Since HCl dissociates completely, the concentration of hydrogen ions [H+][H^+] in solution will be equal to the initial concentration of HCl.
Given: [HCl]=0.0055 M[HCl] = 0.0055 \, M
Therefore: [H+]=0.0055 M[H^+] = 0.0055 \, M
The pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration: pH=−log[H+]\text{pH} = -\log [H^+]
Plugging in the value: pH=−log(0.0055)\text{pH} = -\log(0.0055)
Calculate: log(0.0055)=log(5.5×10−3)=log(5.5)+log(10−3)=0.7404−3=−2.2596\log(0.0055) = \log(5.5 \times 10^{-3}) = \log(5.5) + \log(10^{-3}) = 0.7404 – 3 = -2.2596
So, pH=−(−2.2596)=2.2596≈2.260\text{pH} = -(-2.2596) = 2.2596 \approx 2.260
Additional Notes:
- Since HCl is a strong acid, it fully dissociates, so no equilibrium calculation is necessary.
- The pH scale typically ranges from 0 to 14 for aqueous solutions, where lower pH indicates higher acidity.
- For very dilute strong acid solutions (below about 1 × 10^-6 M), water autoionization affects pH, but 0.0055 M is sufficiently concentrated that we can ignore this.
- Writing the answer to three decimal places is standard practice for precision in chemistry calculations, especially in titrations or analytical chemistry contexts.
Thus, the pH of a 0.0055 M HCl solution is 2.260.