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Chapter 15: Problem 148

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?

Short Answer

Expert verified
HX is the stronger acid at these concentrations.

Step by step solution

01

Calculate Molar Concentration

First, calculate the concentrations of HX and HY in moles per liter. This is done by dividing the mass concentration (\(16.9 \mathrm{~g} / \mathrm{L}\) for HX and \(9.05 \mathrm{~g} / \mathrm{L}\) for HY) by the respective molar mass (180 g/mol for HX and 78 g/mol for HY). This gives you molar concentrations of \[\frac{16.9 \mathrm{~g} / \mathrm{L}}{180 \mathrm{~g} / \mathrm{mol}} = 0.094 \mathrm{~M}\] for HX and \[\frac{9.05 \mathrm{~g} / \mathrm{L}}{78.0 \mathrm{~g} / \mathrm{mol}} = 0.116 \mathrm{~M}\] for HY.
02

Compare Acid Strengths

Since both solutions have the same pH, the concentration of H+ ions is the same in both. A stronger acid will donate more protons and therefore have a higher concentration of H+ ions in solution. But since both solutions have the same pH, it means they have the same concentration of H+ ions. As a result, the acid with the smaller molar concentration (HX) must be the stronger acid, because less of it is needed to achieve the same concentration of H+ ions.

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Most popular questions from this chapter

At \(28^{\circ} \mathrm{C}\) and 0.982 atm, gaseous compound HA has a density of \(1.16 \mathrm{~g} / \mathrm{L}\). A quantity of \(2.03 \mathrm{~g}\) of this compound is dissolved in water and diluted to exactly \(1 \mathrm{~L}\). If the \(\mathrm{pH}\) of the solution is 5.22 (due to the ionization of \(\mathrm{HA}\) ) at \(25^{\circ} \mathrm{C}\), calculate the \(K_{\mathrm{a}}\) of the acid.

Calculate the number of moles of \(\mathrm{KOH}\) in \(5.50 \mathrm{~mL}\) of a \(0.360 \mathrm{M}\) KOH solution. What is the \(\mathrm{pOH}\) of the solution?

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?

You are given two beakers, one containing an aqueous solution of strong acid (HA) and the other an aqueous solution of weak acid (HB) of the same concentration. Describe how you would compare the strengths of these two acids by (a) measuring the \(\underline{p H},\) (b) measuring electrical conductance, (c) studying the rate of hydrogen gas evolution when these solutions are reacted with an active metal such as \(\mathrm{Mg}\) or \(\mathrm{Zn}\).

Without referring to the text, write the formulas of four strong acids and four weak acids.
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