Question

Classify each of the following acids as a strong or weak electrolyte: (a) \(\mathrm{HF}(a q)\) (b) \(\mathrm{HCl}(a q)\) (c) \(\mathrm{HNO}_{3}(a q)\) (d) \(\mathrm{HNO}_{2}(a q)\)

Short answer

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

Step-by-step solution

Understanding Electrolytes

Electrolytes are substances that, when dissolved in water, dissociate into ions and conduct electricity. Strong electrolytes completely ionize in solution, while weak electrolytes only partially ionize.

Identify Strong and Weak Acids

Strong acids are strong electrolytes because they completely dissociate into ions in water. Common strong acids include \( \mathrm{HCl} \), \( \mathrm{HNO}_{3} \), \( \mathrm{HBr} \), and \( \mathrm{H_2SO_4} \). Weak acids are weak electrolytes and only partially dissociate. \( \mathrm{HF} \) and \( \mathrm{HNO}_{2} \) are examples of weak acids.

Classify Each Acid

Review the four acids given:- (a) \( \mathrm{HF}(aq) \) is a weak acid and thus a weak electrolyte.- (b) \( \mathrm{HCl}(aq) \) is a strong acid, making it a strong electrolyte.- (c) \( \mathrm{HNO}_{3}(aq) \) is also a strong acid, thus a strong electrolyte.- (d) \( \mathrm{HNO}_{2}(aq) \) is a weak acid, and therefore a weak electrolyte.

Summarize the Findings

Now that each acid is classified based on dissociation, we have: (a) \( \mathrm{HF} \) – weak electrolyte,(b) \( \mathrm{HCl} \) – strong electrolyte,(c) \( \mathrm{HNO}_{3} \) – strong electrolyte,(d) \( \mathrm{HNO}_{2} \) – weak electrolyte.

Key concepts

Strong Electrolytes

Strong electrolytes are substances that completely dissociate into ions when dissolved in water. This full dissociation allows them to effectively conduct electricity. For an electrolyte to be classified as strong, it must entirely break down in a solution, forming ions. This can include ionic compounds, strong acids, and strong bases.

• Examples of Strong Electrolytes:
  • Strong Acids like hydrochloric acid ( HCl ), nitric acid ( HNO_{3} ).
  • Strong Bases such as sodium hydroxide ( NaOH ).
  • Salts, for instance, sodium chloride ( NaCl ).
• Properties:
  • They fully ionize in water, providing a high concentration of ions.
  • They create solutions that are excellent conductors of electricity.

When testing for strong electrolytes, you can use a simple conductivity test. A solution of a strong electrolyte will light up a bulb or show a high reading on a conductivity meter. This property is crucial for applications requiring high electrical conductivity.

Weak Acids

Weak acids are a type of chemical substance that only partially dissociate into ions in aqueous solutions. Unlike strong acids, which completely ionize, weak acids exist in equilibrium between the ionized and non-ionized forms. This balance results in fewer ions in the solution and consequently weaker electrical conductivity.

• Characteristics of Weak Acids:
  • They do not fully dissociate in water.
  • The non-ionized acid and the ions remain in a dynamic equilibrium.
  • This partial ionization is often represented by a double arrow (↔) in chemical equations.
• Examples of Weak Acids:
  • Hydrofluoric acid ( HF ).
  • Nitrous acid ( HNO_{2} ).
  • Acetic acid ( CH_{3}COOH ).

The presence of fewer ions means weak acids offer less electrical conductivity than strong acids. Despite being weak, some weak acids, like acetic acid, have significant uses in industries and households, indicating their importance beyond just their conductivity properties.

Acid Dissociation

Acid dissociation is the process in which an acid releases a proton ( H^+) and breaks down into its respective ions in solution. This process is key in determining the size and strength of an acid's dissociation.

• The Dissociation Constant (Ka):
  • This constant is a measure of the strength of an acid in solution.
  • The dissociation expression for a weak acid HA is given by: \[ HA(aq) \rightleftharpoons H^+(aq) + A^-(aq) \]
  • The acid dissociation constant ( K_a) is expressed as: \[ K_a = \frac{[H^+][A^-]}{[HA]} \]
  • For strong acids, since they completely dissociate, the K_a value is very high, often difficult to measure precisely. Whereas, for weak acids, K_a is a finite value.
• Factors Influencing Dissociation:
  • Concentration: As the concentration of an acid changes, the degree of its dissociation may also vary.
  • Temperature: Higher temperatures typically increase dissociation rates.

Understanding acid dissociation values helps in predicting the behavior of acids in different solutions. This knowledge is crucial for calculating pH and for various chemical industries that rely on precise acid manipulation.