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The flask shown here contains 10 mL of HCl and a few drops of phenolphthalein indicator
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17. Acid and Base Equilibrium
pH of Strong Acids and Bases
Multiple Choice
A 25.00 mL sample of 0.175 M HCl is being titrated with 0.250 M NaOH. What is the pH when 0 mL of NaOH has been added?
A
1.00
B
13.00
C
7.00
D
0.76
Verified step by step guidance1
Identify the initial conditions: You have a 25.00 mL sample of 0.175 M HCl. Since no NaOH has been added yet, the solution is purely HCl, a strong acid.
Calculate the initial moles of HCl: Use the formula \( \text{moles} = \text{concentration} \times \text{volume} \). Convert the volume from mL to L by dividing by 1000.
Since HCl is a strong acid, it dissociates completely in water. Therefore, the concentration of \( \text{H}^+ \) ions is equal to the concentration of HCl.
Use the formula for pH: \( \text{pH} = -\log[\text{H}^+] \). Substitute the concentration of \( \text{H}^+ \) ions into this formula to find the pH.
Interpret the result: Since no NaOH has been added, the pH should reflect the acidic nature of the solution, which is consistent with the calculated pH value.
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