Problem 3 - Chemistry for Allied Health

Question

Identify each of the following as a strong acid, weak acid, strong base, or weak base. a. \(\mathrm{HCl}\) b. \(\mathrm{NaOH}\) c. KOH d. \(\mathrm{HNO}_{2}\) e. \(\mathrm{HNO}_{3}\) f. HF g. \(\mathrm{NH}_{3}\) h. \(\mathrm{Ba}(\mathrm{OH})_{2}\) i. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\)

Step-by-Step Solution

Answer

a) Strong acid; b) Strong base; c) Strong base; d) Weak acid; e) Strong acid; f) Weak acid; g) Weak base; h) Strong base; i) Weak acid.

Step 1: Identify Strong Acids

Strong acids are those that completely dissociate in water. Common examples include hydrochloric acid (\( \mathrm{HCl} \)), nitric acid (\( \mathrm{HNO}_3 \)), and sulfuric acid (\( \mathrm{H}_2\mathrm{SO}_4 \)). In this list, \( \mathrm{HCl} \) and \( \mathrm{HNO}_3 \) are strong acids.

Step 2: Identify Weak Acids

Weak acids only partially dissociate in water. Examples in the list include \( \mathrm{HNO}_2 \) (nitrous acid), \( \mathrm{HF} \) (hydrofluoric acid), and \( \mathrm{CH}_3\mathrm{CH}_2\mathrm{COOH} \) (propionic acid). These are weak acids.

Step 3: Identify Strong Bases

Strong bases completely dissociate in water and include hydroxides of alkali metals and heavier alkaline earth metals. In this problem, \( \mathrm{NaOH} \), \( \mathrm{KOH} \), and \( \mathrm{Ba(OH)}_2 \) are strong bases.

Step 4: Identify Weak Bases

Weak bases partially dissociate in water or accept a proton rather than dissociate directly. \( \mathrm{NH}_3 \) (ammonia) is a weak base, as it accepts a proton from water to form ammonium.

Key Concepts

Understanding Strong Acids

Strong acids are fascinating because they behave very predictably in water by fully dissociating into ions. This complete separation means that when you add a strong acid like hydrochloric acid (\( \mathrm{HCl} \)) or nitric acid (\( \mathrm{HNO}_3 \)) to water, all of the acid molecules separate into hydrogen ions (\( \mathrm{H}^+ \)) and their respective anions like \( \mathrm{Cl}^- \) or \( \mathrm{NO}_3^- \).
This characteristic makes strong acids excellent at conducting electricity, thanks to all the free ions they release.

• Common strong acids include \( \mathrm{HCl} \), \( \mathrm{HNO}_3 \), and sulfuric acid (\( \mathrm{H}_2\mathrm{SO}_4 \)).
• Since they completely dissociate, their reactions with bases are often more vigorous.

Understanding the behavior of strong acids helps in predicting how a solution will respond in terms of pH change, reactivity, and conductivity.

Exploring Weak Acids

Weak acids are more common in daily life than many might think. Unlike strong acids, weak acids only partially dissociate in water, meaning that only a few of the acid molecules release \( \mathrm{H}^+ \) ions. This partial dissociation results in a higher pH compared to strong acids.
This makes weak acids less corrosive and safer to handle in most cases.

• Examples include nitrous acid (\( \mathrm{HNO}_2 \)), hydrofluoric acid (\( \mathrm{HF} \)), and organic acids like propionic acid (\( \mathrm{CH}_3\mathrm{CH}_2\mathrm{COOH} \)).
• Their dissociation extent can be described by an equilibrium expression where both the ionized and unionized forms are present.

Knowing about weak acids is crucial in biology and environmental science, as these acids often occur naturally and play significant roles in various biochemical processes.

Delving into Strong Bases

Strong bases are compounds that are quite efficient in affecting pH because they dissociate completely in water, releasing hydroxide ions (\( \mathrm{OH}^- \)). This swift release of \( \mathrm{OH}^- \) ions makes them very good at neutralizing acids.
Common strong bases include

• sodium hydroxide (\( \mathrm{NaOH} \)),
• potassium hydroxide (\( \mathrm{KOH} \)), and
• barium hydroxide (\( \mathrm{Ba(OH)}_2 \)).

Their strong dissociating nature makes them useful in industry for things like soap making, cleaning products, and in chemical reactions where altering pH is necessary. Caution is often advised when working with strong bases because their ability to dissolve proteins means they can be corrosive to organic tissues.

Investigating Weak Bases

Weak bases are distinct because they are not fond of releasing \( \mathrm{OH}^- \) ions outright. Instead, they often work by accepting protons (\( \mathrm{H}^+ \)) from their environment, which can increase the pH of a solution.
A classic example is ammonia (\( \mathrm{NH}_3 \)), which grabs a proton from water to form ammonium ion (\( \mathrm{NH}_4^+ \)).
This indirect way of increasing hydroxide concentration makes them gentler compared to strong bases.

• Ammonia is common in household cleaning supplies because of its mild nature.
• Weak bases play important roles in biological systems where subtle changes in pH are needed.

Understanding weak bases is vital for fields like pharmacology and physiology, where maintaining controlled environments is crucial.