Problem 33 - Chemistry in 30 days

Question

Which of the following does not evolve hydrogen gas from \(\mathrm{NaOH}\) ? (a) \(\mathrm{P}\) (b) \(\mathrm{B}\) (c) \(\mathrm{Zn}\) (d) \(\underline{\text { Si }}\)

Step-by-Step Solution

Answer

Silicon (Si) does not evolve hydrogen gas from NaOH.

Step 1: Understand the Reaction of NaOH with Metals

Sodium hydroxide (NaOH) reacts with some metals to evolve hydrogen gas. Typically, metals lower than hydrogen in the reactivity series do not evolve hydrogen gas when reacting with NaOH.

Step 2: Analyze Each Option

Let's consider each option: (a) Phosphorus (P), (b) Boron (B), (c) Zinc (Zn), and (d) Silicon (Si). We need to determine how each of these elements interacts with NaOH.

Step 3: Evaluate the Reaction of Si with NaOH

Silicon (Si) does not react with NaOH to produce hydrogen. It does not behave like typical metals that react with NaOH to release hydrogen gas.

Step 4: Identify the Element That Does Not Evolve Hydrogen

Phosphorus, Boron, and Zinc can show some reactions with NaOH under certain conditions that may release gas. However, Silicon (Si) is more of a metalloid and does not release hydrogen gas when interacting with NaOH in this context.

Key Concepts

Hydrogen Gas Evolution

Hydrogen gas evolution is a key concept when studying the reaction of different elements with sodium hydroxide (NaOH). When certain metals react with NaOH, they can release hydrogen gas. This reaction generally happens because the metals displace hydrogen ions from the NaOH, allowing hydrogen gas to form.
However, not all elements behave the same. It's essential to understand the specific reactivity of each element with NaOH to predict hydrogen gas release.

• Active Metals: Metals such as zinc can react with NaOH under specific conditions to evolve hydrogen gas.
• Inert Elements: Elements like silicon, which are metalloids, do not typically engage in such reactions and therefore do not release hydrogen gas with NaOH in a straightforward manner.

Reactivity Series

The reactivity series is a fundamental tool in chemistry, helping us predict how different metals will react with various substances including NaOH. This series ranks elements in order of their chemical reactivity. Metals higher in the series will react more vigorously, often displacing hydrogen.
Understanding where a metal stands in this series helps to estimate whether hydrogen gas will evolve during a reaction with NaOH.

• Zinc, for instance, is higher on the reactivity scale than hydrogen, which enables the evolution of hydrogen gas when it reacts with NaOH.
• On the other hand, metalloids like silicon, not being true metals, don't follow the reactivity pattern seen in most metals and typically will not participate in hydrogen evolution with NaOH.

Metals and Metalloids

Metals and metalloids differ significantly in their chemical properties, which influences how they react with substances like sodium hydroxide.
Metals typically have the ability to lose electrons easily, making them likely candidates to displace hydrogen from NaOH and form hydrogen gas.

• Metals: For example, zinc falls under metals and can interact with NaOH to release hydrogen gas due to its tendency to lose electrons.
• Metalloids: Silicon is a metalloid, combining properties of metals and non-metals but does not readily lose electrons to NaOH, thus not releasing hydrogen gas.

This distinction informs why under the given choice options, silicon (Si) does not evolve hydrogen gas in reaction with NaOH.