Question

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

Short answer

The order of increasing pH for the 0.10 M solutions is e, c, d, a, b.

Step-by-step solution

Identify the nature of each chemical

We will now identify the nature of each chemical, whether it acts as an acid, base or a salt. a. \(\mathrm{NH}_{3}\): Ammonia is a weak base. b. KOH: Potassium hydroxide is a strong base. c. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\): Acetic acid is a weak acid. d. KCl: Potassium chloride is a salt derived from a strong acid (HCl) and a strong base (KOH). e. HCl: Hydrochloric acid is a strong acid.

Determine the dissociation/ionization in water

Each of these chemicals will dissociate/ionize in water to release ions. We determine how these ions will affect the pH. a. \(\mathrm{NH}_{3}\): William dissociate in water to form \(\mathrm{NH}_{4}^+\) and \(\mathrm{OH}^-\) ions. Since it is a weak base, OH- ions will have a small concentration, resulting in a pH slightly above 7. b. KOH: It will ionize in water completely, forming K+ and OH- ions. The concentration of OH- ions will be much higher, resulting in a much higher pH. c. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\): It will donate protons to water molecules and form \(\mathrm{H}_{3} \mathrm{O}^+\) ions. As a weak acid, it will result in a pH slightly below 7. d. KCl: Being a salt formed from a strong acid and a strong base, it will not have any significant acidic or basic effect on the water. It will be considered neutral with pH around 7. e. HCl: It will ionize completely, dissociating into H+ ions (protons) and Cl- ions. The concentration of H+ ions will increase, resulting in a pH much lower than 7.

Rank the solutions in order of increasing pH

Based on the nature and dissociation/ionization of each solution, we can now rank the solutions in order of increasing pH. 1. HCl (strong acid) 2. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) (weak acid) 3. KCl (neutral) 4. \(\mathrm{NH}_{3}\) (weak base) 5. KOH (strong base) So the order is e, c, d, a, b.

Key concepts

Weak Acids

Weak acids are substances that only partially dissociate in water. This means that not all of their molecules break apart into ions. For example, acetic acid ( HC_{2}H_{3}O_{2} ) is a classic weak acid. When placed in water, it releases some H^+ ions into the solution, but most of the HC_{2}H_{3}O_{2} molecules remain intact.

Characteristics of weak acids include:

• Partial ionization in solution.
• Lower concentration of H^+ ions compared to strong acids.
• Slightly acidic, resulting in a pH that is somewhat below 7.

Weak acids like acetic acid are useful in various household and industrial applications due to their milder acidic nature compared to strong acids.

Strong Acids

Strong acids fully dissociate in water, meaning they release all their H^+ ions into the solution. Hydrochloric acid (HCl) is a perfect example of a strong acid. When dissolved in water, it completely separates into H+ and Cl- ions.

Key features of strong acids:

• Complete ionization in water.
• Significant increase in the number of H^+ ions.
• Results in a very low pH, typically below 3.

The ability of strong acids to completely dissociate makes them very reactive and essential in fields like chemical manufacturing and laboratory settings for reactions requiring highly acidic conditions.

Weak Bases

Weak bases are substances that do not completely ionize in water. They only partially release OH^- ions when they dissolve. Ammonia ( NH_3 ) is a common example of a weak base. In water, NH_3 reacts with H_2O to form NH_4^+ and OH^- ions, but only a small percentage of molecules do this.

Key characteristics of weak bases include:

• Partial ionization in solution.
• Lower concentration of OH^- ions compared to strong bases.
• Slightly basic, leading to a pH that is just above 7.

Weak bases are often used in various products like cleaning supplies and pharmaceuticals due to their moderate basicity.

Strong Bases

Strong bases are distinguished by their complete ionization in water, meaning they fully release OH^- ions into the solution. Potassium hydroxide (KOH) is an excellent example of a strong base. When KOH dissolves in water, it splits entirely into K+ and OH- ions.

Characteristics of strong bases include:

• Complete ionization in water.
• High concentration of OH^- ions.
• Results in a high pH, usually much higher than 7.

Because of their high reactivity, strong bases are widely used in industries such as soap manufacturing and chemical processing where high pH solutions are required.

Neutral Salts

Neutral salts are compounds formed from the neutralization reaction of a strong acid and a strong base. Such salts, when dissolved in water, do not change the pH significantly. Potassium chloride (KCl) is a primary example of a neutral salt. It results from the reaction of hydrochloric acid (HCl) with potassium hydroxide (KOH).

Attributes of neutral salts include:

• Do not affect the pH of the solution.
• Composed of ions that neither donate nor accept H^+ or OH^- ions significantly.
• Resulting solutions often have a pH close to 7.

Neutral salts like KCl are found in a variety of household and industrial applications due to their non-reactive nature.