Question

Classify each of the following as a strong acid, weak acid, strong base, or weak base in aqueous solution. a. ${\mathrm{HNO}}_2$ b. HNO ${}_3$ c. ${\mathrm{CH}}_3{\mathrm{NH}}_2$ d. $\mathrm{NaOH}$ e. ${\mathrm{NH}}_3$ f. $\mathrm{HF}$ g. $\mathrm{HC}-\mathrm{OH}$ h. $\mathrm{Ca}(\mathrm{OH}{)}_2$ i. ${\mathrm{H}}_2{\mathrm{SO}}_4$

Short answer

a. HNO${}_2$ - Weak Acid b. HNO${}_3$ - Strong Acid c. CH${}_3$NH${}_2$ - Weak Base d. NaOH - Strong Base e. NH${}_3$ - Weak Base f. HF - Weak Acid g. HCOH - Weak Acid h. Ca(OH)${}_2$ - Strong Base i. H${}_2$SO${}_4$ - Strong Acid

Step-by-step solution

To identify strong acids and strong bases, we refer to a list of common strong acids, such as HCl, HNO${}_3$, H${}_2$SO${}_4$, HI, HBr, and HClO${}_4$, and a list of common strong bases, such as NaOH, KOH, and Ca(OH)${}_2$. Here, we see that some of the substances in the exercise are on these lists: - HNO${}_3$ is a strong acid - NaOH is a strong base - Ca(OH)${}_2$ is a strong base #Step 2: Identify weak acids and weak bases in the list#

For weak acids and weak bases, we can look at their general properties and formulas. Weak acids are typically molecular substances that only partially ionize in water, whereas weak bases only partially accept protons from water molecules. Now, let's identify the remaining substances: a. HNO${}_2$ - This is a weak acid because it will only partially ionize in water. c. CH${}_3$NH${}_2$ - This is a weak base because it can accept protons but not as effectively as strong bases. e. NH${}_3$ - This is a weak base because it can accept protons, but not as effectively as strong bases. f. HF - This is a weak acid because it only partially ionizes in water. g. HCOH - This is a weak acid because it contains a hydrogen ion (H${}^{+}$) that can be donated, but it only partially ionizes in water. Now we have classified all the given substances in the exercise: a. HNO${}_2$ - Weak Acid b. HNO${}_3$ - Strong Acid c. CH${}_3$NH${}_2$ - Weak Base d. NaOH - Strong Base e. NH${}_3$ - Weak Base f. HF - Weak Acid g. HCOH - Weak Acid h. Ca(OH)${}_2$ - Strong Base i. H${}_2$SO${}_4$ - Strong Acid

Key concepts

Strong Acids

Strong acids are acids that completely dissociate in water, releasing all their hydrogen ions (H${}^{+}$) into the solution. This means they ionize fully, leading to a high concentration of hydrogen ions which makes them very effective in increasing the acidity of a solution.
${\text{HNO}}_3$ (nitric acid) and ${\text{H}}_2{\text{SO}}_4$ (sulfuric acid) are strong acids mentioned in our exercise.

Common characteristics of strong acids include:

• Completely ionize in water
• Produce a high concentration of H${}^{+}$ ions
• Have a very low pH value, usually below 1-2
• Examples include: HCl, HBr, HI, HNO${}_3$, HClO${}_4$, H${}_2$SO${}_4$

This complete ionization is what gives them their strong acidic properties, making them suitable for reactions requiring a consistent and strong acidic environment.

Weak Acids

Weak acids are those that only partially dissociate in water, meaning that only a small amount of their hydrogen ions (H${}^{+}$) are released into the solution. This means they do not ionize completely, which results in a lower concentration of hydrogen ions compared to strong acids.
Examples of weak acids from the exercise include ${\text{HNO}}_2$ (nitrous acid) and HF (hydrofluoric acid).

Let's highlight some key features of weak acids:

• Only partially ionize in water
• Produce fewer H${}^{+}$ ions compared to strong acids
• Have a higher pH value compared to strong acids, typically between 3-6
• Examples include: ${\text{CH}}_3\text{COOH}$ (acetic acid), ${\text{H}}_2{\text{CO}}_3$ (carbonic acid), HF, ${\text{HNO}}_2$

Weak acids are crucial in situations where a gentle, controlled acid environment is needed, allowing precision in biochemical reactions without a large pH change.

Strong Bases

Strong bases are substances that dissociate completely in water, therefore readily providing large quantities of hydroxide ions (OH${}^{-}$) into the solution. This complete dissociation makes them highly effective in neutralizing acids and therefore increasing the pH of a solution.
Examples of strong bases from our exercise include $\text{NaOH}$ (sodium hydroxide) and ${\text{Ca(OH)}}_2$ (calcium hydroxide).

Characteristics of strong bases include:

• Completely dissociate in water
• Produce high concentrations of OH${}^{-}$ ions
• Have a very high pH value, often greater than 12
• Examples include: $\text{NaOH}$, $\text{KOH}$, ${\text{Ca(OH)}}_2$

This complete dissociation allows strong bases to effectively neutralize acids, making them perfect choices for chemical reactions requiring high alkalinity.

Weak Bases

Weak bases are compounds that do not fully accept protons or dissociate in water, leading to only a small number of hydroxide ions (OH${}^{-}$) or other anions forming in solution. This partial dissociation results in a lower basic pH, compared to strong bases.
Examples from the exercise include ${\text{CH}}_3{\text{NH}}_2$ (methylamine) and ${\text{NH}}_3$ (ammonia).

Key points about weak bases:

• Partially dissociate in water
• Produce fewer OH${}^{-}$ ions than strong bases
• Have a pH that is less than that of strong bases, typically between 8-11
• Examples include: ${\text{NH}}_3$, ${\text{CH}}_3{\text{NH}}_2$, ${\text{C}}_6{\text{H}}_5{\text{NH}}_2$ (aniline)

Weak bases are ideal for processes where over-neutralization could be problematic, as they enable more controlled and gradual increases in pH.