Question

Classify each of the following as a strong or weak acid or base. (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{HCNO}\) (c) \(\mathrm{Mg}(\mathrm{OH})_{2}\) (d) \(\mathrm{HClO}_{3}\)

Short answer

(a) Weak Base, (b) Weak Acid, (c) Weak Base, (d) Strong Acid.

Step-by-step solution

Understanding Acids and Bases

We need to determine if each given compound is a strong or weak acid or base. Strong acids and bases dissociate completely in water, while weak ones do not fully dissociate.

Classify  NH_{3} 10 as an Acid or Base

Ammonia,  NH_{3} 10, is a base. As it only partially accepts protons when dissolved in water, it is classified as a weak base.

Classify  HCNO 10

Cyanoic acid,  HCNO 10, is an acid that does not completely dissociate in water, thus it is considered a weak acid.

Classify  Mg(OH)_{2} 10

Magnesium hydroxide,  Mg(OH)_{2} 10, is a base that does not dissolve well in water, making it a weak base.

Classify  HClO_{3} 10

Chloric acid,  HClO_{3} 10, is an acid that fully dissociates in water. Therefore, it is considered a strong acid.

Key concepts

Strong Acids

Strong acids are special because they completely dissociate in water. This means that when a strong acid is added to water, it fully breaks apart into ions. For example, if you take chloric acid (\(\mathrm{HClO}_{3}\)), it separates entirely into hydrogen ions (\(\mathrm{H}^+\)) and chlorate ions (\(\mathrm{ClO}_{3}^{-}\)). This complete dissociation is what makes an acid "strong". It's essential to understand this process because it plays a fundamental role in reactions involving acids. When you're dealing with strong acids,

• they have a very low pH (below 3)
• they are strong electrolytes, so they conduct electricity well in solution
• they react vigorously in chemical reactions, especially with bases

Always handle these acids with care due to their powerful reactivity.

Weak Acids

Weak acids are quite different from strong acids because they do not fully dissociate in water. Instead, when you add a weak acid like cyanoic acid (\(\mathrm{HCNO}\)) to water, most of it stays as whole molecules, with only a small fraction breaking into ions.This incomplete ionization means:

• weak acids generally have a higher pH than strong acids (usually between 3 and 7)
• they are weak electrolytes, so they conduct electricity poorly in solution
• they engage less vigorously in reactions compared to strong acids

Weak acids often reach a kind of balance called an equilibrium in solution, where both the dissociated ions and the whole acid molecules coexist. This equilibrium is key to many processes in chemistry, including buffer solutions.

Strong Bases

Strong bases, similar to strong acids, dissociate completely in water. When a strong base like sodium hydroxide (\(\mathrm{NaOH}\)) dissolves in water, it fully splits into sodium ions (\(\mathrm{Na}^+\)) and hydroxide ions (\(\mathrm{OH}^-\)). This full dissociation gives strong bases their characteristic properties:

• they have a very high pH (above 11)
• they are strong electrolytes, effectively conducting electric current
• they react powerfully, especially when neutralizing acids

Due to their complete ionization, strong bases are essential in many industrial applications. Always employ caution when using strong bases, as their reactivity can cause significant chemical burns.

Weak Bases

Weak bases, unlike strong ones, do not dissociate completely in solution. When a weak base such as ammonia (\(\mathrm{NH}_{3}\)) is mixed with water, only a small number of molecules will accept hydrogen ions from water to form hydroxide ions (\(\mathrm{OH}^-\)).The incomplete ionization results in:

• relatively lower pH than strong bases (usually between 7 and 11)
• weak electrolytic properties, so they don't conduct electricity well
• less intense reactions compared to strong bases

Because a substantial portion of the base remains undissociated, weak bases play an essential role in biological and environmental systems, helping to maintain pH balance.