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A solution of HCl has = 0.01 M. What is the pH of this solution? use. –2 –1 1 2
17. Acid and Base Equilibrium
The pH Scale
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If you decrease the pH of a solution from pH = 2 to pH = 1, which of the following statements is TRUE? Assume the temperature is held constant.
A
There are no OH⁻ ions in the solution.
B
It changes the Kw value for the solution.
C
The H+ concentration has increased tenfold.
D
The solution becomes less acidic.
Verified step by step guidance1
Understand the pH scale: The pH scale is logarithmic, meaning each whole number change in pH represents a tenfold change in hydrogen ion concentration \((\text{H}^+)\). A decrease in pH indicates an increase in \(\text{H}^+\) concentration.
Calculate the change in \(\text{H}^+\) concentration: When the pH decreases from 2 to 1, the \(\text{H}^+\) concentration increases by a factor of 10. This is because \(\text{pH} = -\log[\text{H}^+]\), so a decrease in pH by 1 unit corresponds to a tenfold increase in \(\text{H}^+\) concentration.
Consider the statement about OH⁻ ions: Even at low pH, there are still \(\text{OH}^-\) ions present due to the autoionization of water, although their concentration is very low compared to \(\text{H}^+\) ions.
Evaluate the statement about Kw: The ion product of water \((K_w)\) is constant at a given temperature, typically \(1.0 \times 10^{-14}\) at 25°C. Changing the pH does not affect \(K_w\).
Assess the statement about acidity: A decrease in pH from 2 to 1 means the solution becomes more acidic, not less. The \(\text{H}^+\) concentration increases, making the solution more acidic.
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