Problem 36
Question
An aqueous solution of an unknown solute is tested with litmus paper and found to be acidic. The solution is weakly conducting compared with a solution of \(\mathrm{NaCl}\) of the same concentration. Which of the following substances could the unknown be: \(\mathrm{KOH}\), \(\mathrm{NH}_{3}, \mathrm{HNO}_{3}, \mathrm{KClO}_{2}, \mathrm{H}_{3} \mathrm{PO}_{3}, \mathrm{CH}_{3} \mathrm{COCH}_{3}\) (acetone)?
Step-by-Step Solution
Verified Answer
The unknown substance could be \(\mathrm{H}_{3} \mathrm{PO}_{3}\) (phosphorous acid), as it is acidic and a weak electrolyte.
1Step 1: Eliminate non-acidic compounds
As we know that the solution is acidic, we can start by eliminating any substance that is not acidic or does not produce acidic solutions:
1. KOH: A strong base, not acidic.
2. NH3: A weak base, not acidic.
So now, our list of possible substances is: HNO3, KClO2, H3PO3, or acetone (CH3COCH3).
2Step 2: Eliminate strong acids
Since the solution is weakly conducting, it indicates that the solute is a weak electrolyte. Thus, strong acids can't be the unknown substance:
1. HNO3: A strong acid (strong electrolyte), not a weakly conducting substance.
Now, our list of possible substances is: KClO2, H3PO3, or acetone (CH3COCH3).
3Step 3: Investigate remaining substances
Finally, we will evaluate the remaining substances regarding their acidic nature and weakly-conducting property:
1. \(\mathrm{KClO}_{2}\) - When dissolved in water, it forms a neutral solution, so it can't be our unknown substance.
2. \(\mathrm{H}_{3} \mathrm{PO}_{3}\) - Phosphorous acid (H3PO3) is a weak acid (weak electrolyte), so it fits the criteria of being acidic and weakly conducting.
3. \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) - Acetone is a weakly-conducting organic compound that does not act as an acid when dissolved in water, so it can't be our unknown substance.
So based on the given properties, the unknown substance could be: \(\mathrm{H}_{3} \mathrm{PO}_{3}\) (phosphorous acid).
Key Concepts
Aqueous SolutionsElectrolytesAcid-Base Reactions
Aqueous Solutions
An aqueous solution is simply a solution where water acts as the solvent. Many chemical reactions and processes occur in these aqueous environments, whether in nature or in a laboratory setting.
Water is known as the 'universal solvent' because it dissolves many substances, which results in what we call an aqueous solution. When substances dissolve, they disperse evenly throughout the water, becoming part of this solution.
In our aqueous solution with the unknown solute, the litmus paper test revealed it to be acidic. This means hydrogen ions ( H^+ ) were abundant. In acidic aqueous solutions, there is always an excess of hydrogen ions, which is a key factor influencing their chemical behavior.
Water is known as the 'universal solvent' because it dissolves many substances, which results in what we call an aqueous solution. When substances dissolve, they disperse evenly throughout the water, becoming part of this solution.
In our aqueous solution with the unknown solute, the litmus paper test revealed it to be acidic. This means hydrogen ions ( H^+ ) were abundant. In acidic aqueous solutions, there is always an excess of hydrogen ions, which is a key factor influencing their chemical behavior.
- The solvent is water.
- Acidity or basicity in these solutions is determined by the presence of hydrogen or hydroxide ions respectively.
- Solutions can conduct electricity; however, the conductivity depends on the type and strength of the dissolved ions.
Electrolytes
Electrolytes refer to substances that, when dissolved in water, dissociate into ions and make the solution capable of conducting electricity.
Conductivity in a solution is determined by the concentration and type of ions present. Strong electrolytes dissociate completely, producing a solution that conducts electricity well, while weak electrolytes only partially dissociate, leading to weak electrical conductivity.
In the exercise, the solution was weakly conducting, suggesting that the unknown solute was a weak electrolyte. Weak acids, like H_3PO_3 , fall into this category because they only partially ionize in water. This partial ionization leaves fewer ions in the solution, which results in lower conductivity compared to a strong electrolyte like NaCl.
Conductivity in a solution is determined by the concentration and type of ions present. Strong electrolytes dissociate completely, producing a solution that conducts electricity well, while weak electrolytes only partially dissociate, leading to weak electrical conductivity.
In the exercise, the solution was weakly conducting, suggesting that the unknown solute was a weak electrolyte. Weak acids, like H_3PO_3 , fall into this category because they only partially ionize in water. This partial ionization leaves fewer ions in the solution, which results in lower conductivity compared to a strong electrolyte like NaCl.
- Substances that dissociate into ions when dissolved.
- Weak electrolytes partially dissociate, leading to weak conductivity.
- Conductivity is a key indicator of the presence and type of ions in a solution.
Acid-Base Reactions
Acid-base reactions are fundamental chemical reactions where acids donate hydrogen ions (
H^+
), while bases accept them. This exchange of ions causes a variety of reactions and transformations in solutions.
Weak acids, like phosphorous acid ( H_3PO_3 ) found in our exercise, only partially donate their hydrogen ions. These acids exemplify high pH values, but not enough ion production to be considered strong acids.
These reactions are important in natural and industrial processes, including digestion, agriculture, and manufacturing. In an aqueous environment, the properties and strength of acids and bases determine how they react with each other and with other substances. This exercise underscores the importance of understanding the strength and properties of acids in determining the behavior of a solution.
Weak acids, like phosphorous acid ( H_3PO_3 ) found in our exercise, only partially donate their hydrogen ions. These acids exemplify high pH values, but not enough ion production to be considered strong acids.
These reactions are important in natural and industrial processes, including digestion, agriculture, and manufacturing. In an aqueous environment, the properties and strength of acids and bases determine how they react with each other and with other substances. This exercise underscores the importance of understanding the strength and properties of acids in determining the behavior of a solution.
- Reactions involve the transfer of H^+ ions.
- Weak acids only partly ionize in water, affecting their reactivity and conductivity.
- Understanding acid strength is crucial in predicting reaction outcomes.
Other exercises in this chapter
Problem 34
State whether each of the following statements is true or false. Justify your answer in each case. (a) \(\mathrm{NH}_{3}\) contains no \(\mathrm{OH}^{-}\) ions,
View solution Problem 35
Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance existsin aqueous solution entirely in molecu
View solution Problem 37
Classify each of the following substances as a nonelectrolyte, weak electrolyte, or strong electrolyte in water: (a) HF, (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \ma
View solution Problem 38
Classify each of the following aqueous solutions as a nonelectrolyte, weak electrolyte, or strong electrolyte: (a) \(\mathrm{PbCl}_{2}\), (b) \(\mathrm{N}\left(
View solution