Question

Arrange the following 0.10 $M$ solutions in order of most acidic to most basic. $\begin{array}{llllll}& \text{ KOH, }& {\text{ KNO }}_3,& \text{ KCN, }& \text{ NH\_Cl, }& \text{ HCl }\end{array}$

Short answer

The order of the 0.10 M solutions from most acidic to most basic is: HCl (strong acid), NH4Cl (weak acid), KNO3 (neutral), KCN (weak base), and KOH (strong base).

Step-by-step solution

1. Identify the nature of each solution

For each given substance, determine their role as an acid or base once they dissolve in water: 1. KOH: The hydroxide ion (OH-) is a strong base. 2. KNO3: The nitrate ion (NO3-) doesn't react with water, making it neutral. 3. KCN: The cyanide ion (CN-) reacts with water as a weak base. 4. NH4Cl: The ammonium ion (NH4+) reacts with water as a weak acid. 5. HCl: The hydrogen ion (H+) is a strong acid.

2. Order the solutions from the most acidic to the most basic

Using the information on the nature of each solution obtained in the previous step, arrange the solutions from the most acidic to the most basic: 1. HCl (strong acid) 2. NH4Cl (weak acid) 3. KNO3 (neutral) 4. KCN (weak base) 5. KOH (strong base) So, the final order is: HCl, NH4Cl, KNO3, KCN, and KOH.

Key concepts

pH scale

The pH scale is a numeric scale used to specify the acidity or basicity of an aqueous solution. pH stands for 'potential of Hydrogen' or 'power of Hydrogen'. It is a logarithmic scale, which means each whole pH value below 7 is ten times more acidic than the next higher value.

For instance, a solution with a pH of 3 is ten times more acidic than one with a pH of 4 and a hundred times more acidic than a pH of 5. The pH scale typically ranges from 0 to 14, with 7 being neutral. Anything below 7 is considered acidic and anything above 7 is basic (or alkaline).

Understanding the pH scale is crucial when dealing with chemical solutions, as it directly associates with the concentration of hydrogen ions ($H^{+}$) in a solution. The pH of a solution is calculated by using the formula $pH=-\text{log}\text{(}[H^{+}]$ \), where $[H^{+}]$ represents the molar concentration of hydrogen ions. The lower the pH value, the greater the acidity and the higher the concentration of hydrogen ions in the solution. Conversely, a higher pH value indicates a lower concentration of hydrogen ions and a more basic solution.

acid-base reactions

Acid-base reactions are chemical processes that involve the transfer of protons (hydrogen ions, $H^{+}$) between a pair of compounds. These are among the most common chemical processes and are central to many biological and environmental systems.

Acids are substances that can donate a hydrogen ion to another substance in a chemical reaction; they are proton donors. Bases, conversely, are proton acceptors that can take up a hydrogen ion. When an acid and a base react, they form water and a salt in a neutralization reaction. The general form of an acid-base reaction is:$\text{acid}+\text{base}\to \text{salt}+\text{water}$

For example, hydrochloric acid ($HCl$) and sodium hydroxide ($NaOH$) react to form sodium chloride ($NaCl$), a salt, and water ($H_{2}O$). It's important to recognize the role of the solvent, often water, in facilitating acid-base reactions. In aqueous solutions, water can act as both an acid and a base, making these reactions more complex and varied.

aqueous solutions chemistry

Chemistry of aqueous solutions involves the behaviors of substances dissolved in water, which is often the solvent of choice due to its unique and versatile properties. For a chemical to be a strong acid or base in water, it must dissociate completely into ions - meaning it separates into positively and negatively charged components.

For substances that do not completely dissociate, we define them as weak acids or bases. These aspects are essential when addressing the original exercise. For instance, the strong acid HCl completely dissociates into hydrogen and chloride ions, making the solution highly acidic, while a weak acid like $N{H}_{4}Cl$ only partially dissolves into $N{H}_4^{+}$ and $C{l}^{-}$ ions.

The chemistry of these aqueous solutions is influenced by the degree of dissociation and the nature of the ions produced. To enhance students' understanding, it is helpful to discuss the conductivity and reactivity of these solutions, which vary based on their ionic strength and can be directly related to the pH scale and acid-base reactions we previously explored.