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Chapter 15: Problem 12

Define \(\mathrm{pH}\). Why do chemists normally choose to discuss the acidity of a solution in terms of pH rather than hydrogen ion concentration, \(\left[\mathrm{H}^{+}\right] ?\)

Short Answer

Expert verified
pH is the negative logarithm (base 10) of the activity of the hydrogen ions (H+) in a solution. Chemists use pH to discuss acidity because it simplifies the wide range of potential hydrogen ion concentrations, and it represents an exponential scale that aligns with the nature of acid/base reactions.

Step by step solution

01

Definition of pH

pH is a scale used to specify the acidity or basicity of an aqueous solution. It is defined as the negative logarithm (base 10) of the activity of the hydrogen ions (H+) in a solution. Mathematically, it can be expressed as: \( pH = -\log [\mathrm{H}^{+}] \)
02

Explanation for discussing acidity in terms of pH

First, the range of \([\mathrm{H}^{+}]\) in solutions is quite wide, from around 1 M in strong acids to 10^-14 M in strong bases. Using the pH scale, which ranges from 0 to 14, simplifies these numbers. Second, a change in one unit of pH represents a tenfold change in the hydrogen ion concentration. This aligns with the exponential changes in \([\mathrm{H}^{+}]\) concentrations when mixing acids/bases with water, making pH a more intuitive measure.

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Most popular questions from this chapter

Like water, liquid ammonia undergoes autoionization: $$ \mathrm{NH}_{3}+\mathrm{NH}_{3} \rightleftharpoons \mathrm{NH}_{4}^{+}+\mathrm{NH}_{2}^{-} $$ (a) Identify the Brønsted acids and Brønsted bases in this reaction. (b) What species correspond to \(\mathrm{H}^{+}\) and \(\mathrm{OH}^{-}\) and what is the condition for a neutral solution?

Consider the two weak acids HX (molar mass = \(180 \mathrm{~g} / \mathrm{mol}\) ) and \(\mathrm{HY}\) (molar mass \(=78.0 \mathrm{~g} / \mathrm{mol}\) ). If a solution of \(16.9 \mathrm{~g} / \mathrm{L}\) of \(\mathrm{HX}\) has the same \(\mathrm{pH}\) as one containing \(9.05 \mathrm{~g} / \mathrm{L}\) of \(\mathrm{HY},\) which is the stronger acid at these concentrations?

Hydrocyanic acid (HCN) is a weak acid and a deadly poisonous compound -in the gaseous form (hydrogen cyanide) it is used in gas chambers. Why is it dangerous to treat sodium cyanide with acids (such as HCl) without proper ventilation?

Predict whether a solution containing the salt \(\mathrm{K}_{2} \mathrm{HPO}_{4}\) will be acidic, neutral, or basic.

Which of the following has a higher pH: (a) \(0.20 \mathrm{M}\) \(\mathrm{NH}_{3},\) (b) \(0.20 \mathrm{M} \mathrm{NaOH} ?\)
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