Papaverine hydrochloride (abbreviated papH^+ Cl^-; molar mass =378.85 g / mol ) is a drug that

step 1 All right, guys. Zoom problem 122 at Chapter 14. So papyrene hydrochloride is a drug that belong

Papaverine hydrochloride (abbreviated papH^+ Cl^-; molar...

Papaverine hydrochloride (abbreviated $\mathrm{papH}^{+} \mathrm{Cl}^{-}$; molar mass $=378.85 \mathrm{~g} / \mathrm{mol}$ ) is a drug that belongs to a group of medicines called vasodilators, which cause blood vessels to expand, thereby increasing blood flow. This drug is the conjugate acid of the weak base papaverine (abbreviated pap; $K_{\mathrm{b}}=$ $8.33 \times 10^{-9}$ at $35.0^{\circ} \mathrm{C}$ ). Calculate the pH of a $30.0-\mathrm{mg} / \mathrm{mL}$ aqueous dose of $\mathrm{papH}^{+} \mathrm{Cl}^{-}$prepared at $35.0^{\circ} \mathrm{C}$. $K_{\mathrm{w}}$ at $35.0^{\circ} \mathrm{C}$ is $2.1 \times 10^{-14}$.

Key Concepts

Molarity and Concentration Conversions

Molarity, defined as the number of moles of solute per liter of solution, is a key concentration unit in chemistry. Converting from mass concentration (such as mg/mL) to molarity requires the molar mass of the compound. This conversion is fundamental to determining the number of moles of a substance in solution, which is necessary for quantitative analyses and equilibrium calculations.

Acid-Base Equilibrium

Acid-base equilibrium involves the reversible reaction in which acids donate protons to bases, establishing a balance between the forward and reverse reactions. This concept is central to understanding how solutions attain a certain pH, especially in systems where weak acids or bases are present and do not fully dissociate.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs are species formed when an acid loses a proton and becomes its conjugate base, or when a base gains a proton to form its conjugate acid. This relationship is crucial in predicting the direction of acid-base reactions and in understanding the behavior of weak acids and bases in solution.

Relationship Between Kw, Ka, and Kb

The interrelationship between the ion-product constant for water (Kw), the acid dissociation constant (Ka), and the base dissociation constant (Kb) is expressed as Ka × Kb = Kw. This connection is essential for converting Kb values of weak bases to Ka values of their conjugate acids, which is often necessary for calculating the pH of solutions containing weak acids.

Weak Acid pH Calculation

Calculating the pH of a weak acid solution involves establishing an equilibrium expression for the acid's partial dissociation in water. Using the acid dissociation constant (Ka), one can determine the concentration of hydrogen ions produced, often employing approximations for weak acids, and subsequently compute the pH by taking the negative logarithm of the hydrogen ion concentration.

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