Question

Rank the following \(0.10 M\) solutions in order of increasing pH. a. \(\mathrm{NH}_{3}\) d. \(\mathrm{KCl}\) b. \(\mathrm{KOH}\) e. \(\mathrm{HCl}\) c. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\)

Short answer

The order of increasing pH for the given 0.10 M solutions is: e. \(\mathrm{HCl}\), c. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\), d. \(\mathrm{KCl}\), a. \(\mathrm{NH}_{3}\), and b. \(\mathrm{KOH}\).

Step-by-step solution

Identify the nature of each solution

Begin by identifying the nature of each given compound (acidic, basic, or neutral) when dissolved in water. a. \(\mathrm{NH}_{3}\) - Ammonia is a weak base. d. \(\mathrm{KCl}\) - Potassium chloride is a neutral salt. b. \(\mathrm{KOH}\) - Potassium hydroxide is a strong base. e. \(\mathrm{HCl}\) - Hydrochloric acid is a strong acid. c. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) - Acetic acid is a weak acid.

Compare acidic and basic strengths

Now we need to compare the acidic and basic strengths of these compounds: Strong acids, like HCl, will have the lowest pH. Among bases, the strong base (KOH) will have the highest pH. Weak acids and weak bases will have pH values in the middle range. Neutral salts like KCl will have a pH of 7, which is between acidic and basic pH values.

Rank the solutions by pH

Now we can rank these solutions in order of increasing pH: 1. \(\mathrm{HCl}\) - Strong acid (lowest pH) 2. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) - Weak acid (moderate pH) 3. \(\mathrm{KCl}\) - Neutral salt (pH 7) 4. \(\mathrm{NH}_{3}\) - Weak base (moderate to high pH) 5. \(\mathrm{KOH}\) - Strong base (highest pH) Thus, the order of increasing pH is: e. \(\mathrm{HCl}\), c. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\), d. \(\mathrm{KCl}\), a. \(\mathrm{NH}_{3}\), and b. \(\mathrm{KOH}\).

Key concepts

Acid-Base Chemistry

Acid-base chemistry is a fundamental concept in chemistry that deals with the nature and interactions of acids and bases. When an acid dissolves in water, it releases hydrogen ions ( H^+ ) into the solution, making it more acidic. Conversely, a base releases hydroxide ions ( OH^− ), which makes the solution more basic. Therefore, the concentration of these ions can affect the pH level of the solution.

Acids can be strong or weak based on their ability to donate H^+ ions. Strong acids, like hydrochloric acid ( HCl ), fully dissociate in water, resulting in a low pH. Weak acids, such as acetic acid ( HC_2H_3O_2 ), do not fully dissociate, so they have a slightly higher pH compared to strong acids.

Similarly, bases can also have different strengths. Strong bases, like potassium hydroxide ( KOH ), completely dissociate in water, providing a high pH. Weak bases, such as ammonia ( NH_3 ), do not dissociate fully, resulting in a moderate pH level. Neutral compounds, like potassium chloride ( KCl ), neither release H^+ nor OH^− ions in water, so they have a pH close to 7.

Amphoteric Compounds

Amphoteric compounds are unique substances that can react as either an acid or a base, depending on the environment they are in. This dual behavior means they can either donate or accept H^+ ions. A common example of an amphoteric compound is water ( H_2O ), which can donate an H^+ to become hydroxide ( OH^− ) or accept an H^+ to become hydronium ( H_3O^+ ).

Amphoteric behavior is crucial in balancing pH levels in various chemical reactions and natural processes. For instance, in biological systems, proteins exhibit amphoteric properties by acting as buffers, which maintain stable pH levels necessary for life.

• Amphoterism is observed in oxides and hydroxides of certain metals like zinc and aluminum.
• Compounds that display amphoteric properties often form complex solutions that make them versatile in industrial and scientific applications.

pH Scale

The pH scale is a tool used to determine how acidic or basic a solution is. It ranges from 0 to 14, where 7 is considered neutral. Solutions with a pH lower than 7 are acidic, and those higher than 7 are basic or alkaline.

The term "pH" stands for "potential of hydrogen" and measures the concentration of hydrogen ions in a solution. Each unit change on the pH scale represents a tenfold change in H^+ concentration, making it logarithmic.

• A solution with a pH of 1 is ten times more acidic than a solution with a pH of 2.
• Similarly, a pH of 13 is ten times more basic than a pH of 12.

Understanding the pH scale is essential, especially in areas like medicine, agriculture, and environmental sciences. By knowing how solutions rank on the pH scale, we can predict chemical reactions, manage soil health, or even ensure safe drinking water.

Having an accurate understanding of the pH scale helps in interpreting and predicting the outcomes of chemical interactions. This understanding is crucial when studying various substances, such as those listed in the given exercise, and aids in practical applications across different fields.