KOH Reactions: Identifying Reactants

Hey chemistry enthusiasts! Let's dive into a classic question about chemical reactions. This one tests your knowledge of how potassium hydroxide (KOH), a strong base, interacts with different substances. The goal is to pinpoint the row where every substance will react when mixed with a KOH solution. Ready to break it down, guys?

Understanding KOH and Its Reactions

Before we jump into the answer choices, let's get our heads around KOH. Potassium hydroxide is a strong base, which means it readily dissociates in water to produce hydroxide ions (OH⁻). These hydroxide ions are the key players in the reactions. They seek out and react with substances that can donate protons (acids), act as electrophiles, or form precipitates. So, when considering the reactivity of substances with KOH, we need to think about their acidic properties, their ability to be attacked by a nucleophile, or if they can form insoluble compounds with potassium or hydroxide ions.

Here's a quick recap of the general types of compounds that will react with KOH:

• Acids: These will neutralize KOH, forming a salt and water. This is a fundamental acid-base reaction.
• Acidic oxides: These react with bases to form salts. For example, sulfur trioxide (SO₃) reacts with KOH.
• Salts of Weak Acids: The hydroxide ions from KOH can react with the cation of a salt to release the weak acid or the weak acid's conjugate base.
• Substances with Electrophilic Centers: Compounds that can be attacked by a nucleophile (like OH⁻) can undergo reactions such as hydrolysis or nucleophilic substitution. For example, alkyl halides (like ethyl chloride, C₂H₅Cl) can react with KOH through an SN2 mechanism, where the hydroxide ion replaces the halide ion.
• Certain Metal Hydroxides: Amphoteric hydroxides (those that can act as both acids and bases) like zinc hydroxide (Zn(OH)₂) and aluminum hydroxide (Al(OH)₃) will react with excess strong base, like KOH.

Now, let's use this knowledge to evaluate the answer choices. Remember, we're looking for the one row where every substance reacts with KOH.

Analyzing the Answer Choices

Let's meticulously go through each of the provided options, dissecting the behavior of each compound with KOH to determine which row contains substances that react completely. This analytical breakdown will help us understand the core chemistry behind the question. Let's start with option A:

• A) $CH_3COO C_2H_5$, $BaCl_2$, $CH_3NH_2$

  • $CH_3COO C_2H_5$ (Ethyl acetate): Esters like ethyl acetate undergo hydrolysis in the presence of a base (KOH). The reaction cleaves the ester bond, producing ethanol and potassium acetate.
  • $BaCl_2$ (Barium chloride): Barium chloride does not react with KOH. Both are salts and, in an aqueous solution, will simply dissociate into their respective ions. No new product formation is expected, which makes this compound not react.
  • $CH_3NH_2$ (Methylamine): Methylamine is a weak base, so it will not react with KOH. In fact, if the salt of methylamine reacted with KOH, the result would be methylamine, but because it is a weak base, it will not react. Methylamine can react with acids. Thus, option A is incorrect because not all substances react.

• B) $CH_3COO H$, $C_6H_5OH$, $Zn(OH)_2$

  • $CH_3COO H$ (Acetic acid): Acetic acid is an organic acid and will react with KOH to form potassium acetate and water through neutralization.
  • $C_6H_5OH$ (Phenol): Phenol is weakly acidic and reacts with KOH, forming potassium phenoxide and water. This reaction is similar to the reaction with acetic acid.
  • $Zn(OH)_2$ (Zinc hydroxide): Zinc hydroxide is amphoteric, meaning it can react with both acids and bases. With KOH, it acts as an acid, forming a zincate complex ion ([Zn(OH)₄]²⁻), demonstrating that it reacts.

• C) $C_6H_5NH_2$, $SO_3$, $Al(OH)_3$

  • $C_6H_5NH_2$ (Aniline): Aniline (aminobenzene) is a very weak base and does not react with KOH. Similar to methylamine from option A, aniline will not react with KOH.
  • $SO_3$ (Sulfur trioxide): Sulfur trioxide is an acidic oxide. It will react with KOH to form potassium sulfate ($K_2SO_4$).
  • $Al(OH)_3$ (Aluminum hydroxide): Aluminum hydroxide is amphoteric. Like zinc hydroxide from option B, aluminum hydroxide reacts with KOH, forming a tetrahydroxoaluminate(III) complex ion ([Al(OH)₄]⁻).

• D) $C_2H_5Cl$, $CO_2$, $NH_3$

  • $C_2H_5Cl$ (Ethyl chloride): Ethyl chloride is an alkyl halide and will undergo a nucleophilic substitution reaction (SN2) with KOH, where the hydroxide ion replaces the chlorine atom, producing ethanol and potassium chloride.
  • $CO_2$ (Carbon dioxide): Carbon dioxide is an acidic oxide and will react with KOH to form potassium carbonate ($K_2CO_3$).
  • $NH_3$ (Ammonia): Ammonia is a weak base and does not react with KOH. Ammonia can react with acids, but since KOH is a base, they will not react.

• E) $C_2H_5OH$, $HCOOH$, $CuCl_2$

  • $C_2H_5OH$ (Ethanol): Ethanol is a weak acid, but does not react with KOH. In fact, ethanol can be produced from the reaction of ethyl chloride from option D with KOH.
  • $HCOOH$ (Formic acid): Formic acid is an organic acid, so it reacts with KOH to form potassium formate and water, which is a neutralization reaction.
  • $CuCl_2$ (Copper(II) chloride): Copper(II) chloride is a salt. KOH will cause precipitation of copper(II) hydroxide. Thus, this reaction will occur, but it's not a direct reaction in the same way as an acid-base neutralization or nucleophilic substitution.

Identifying the Correct Answer

Based on our analysis, the correct answer is B) $CH_3COO H$, $C_6H_5OH$, $Zn(OH)_2$. In this set, all three substances react with KOH:

• Acetic acid ($CH_3COOH$) and phenol ($C_6H_5OH$) are both acidic and will be neutralized by the base KOH.
• Zinc hydroxide ($Zn(OH)_2$) is amphoteric and reacts with the base KOH. Option B is correct because all substances react with KOH. The other options have compounds that are either inert or will not fully react.

Conclusion

So there you have it, guys! We've systematically gone through each answer choice, breaking down the chemical behavior of each compound. Remember, understanding the fundamental principles of acid-base reactions, nucleophilic substitutions, and the properties of different functional groups is key to tackling these types of chemistry problems. Keep practicing and stay curious, and you'll ace those exams! Let me know if you want to explore other chemistry questions or concepts. Keep up the great work! And now, you know how to identify the correct answer through careful analysis and the application of key chemical concepts. Keep practicing, and you'll be acing those chemistry problems in no time! Good luck!