Question

Which of the following pairs liberate a gas when they react with each other: (a) \(\mathrm{Mg}, \mathrm{B}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{Mg}, \mathrm{CO}_{2}\) (c) Fused \(\mathrm{NaOH}, \mathrm{C}\) (d) \(\mathrm{SiO}_{2}, \mathrm{Na}\)

Short answer

Pair (c) \( \text{Fused } \mathrm{NaOH} \) and \( \mathrm{C} \) liberates a gas.

Step-by-step solution

Identify Possible Reactions for (a)

For pair (a) \( \mathrm{Mg} \) and \( \mathrm{B}_{2} \mathrm{O}_{3} \), typically magnesium can reduce metal oxides, but it does not generate a gas with \( \mathrm{B}_{2} \mathrm{O}_{3} \). Instead, magnesium boride is formed.

Identify Possible Reactions for (b)

For pair (b) \( \mathrm{Mg} \) and \( \mathrm{CO}_{2} \), magnesium can react with carbon dioxide to produce magnesium oxide and carbon: \[ 2\mathrm{Mg} + \mathrm{CO}_{2} \rightarrow 2\mathrm{MgO} + \mathrm{C} \]. However, no gas is liberated in this reaction.

Identify Possible Reactions for (c)

For pair (c) fused \( \mathrm{NaOH} \) and \( \mathrm{C} \), carbon reacts with sodium hydroxide to produce sodium carbonate, hydrogen gas, and water: \[ 2\mathrm{NaOH} + 2\mathrm{C} \rightarrow \mathrm{Na}_{2}\mathrm{CO}_{3} + \mathrm{H}_{2}\] Thus, hydrogen gas \( \mathrm{H}_2 \) is liberated in this reaction.

Identify Possible Reactions for (d)

For pair (d) \( \mathrm{SiO}_{2} \) and \( \mathrm{Na} \), no reaction occurs that liberates a gas. Silicon dioxide is stable and does not release any gas on reaction with sodium.

Conclusion

From the analysis of each pair, it is concluded that only pair (c) which involves reaction of fused \( \mathrm{NaOH} \) with \( \mathrm{C} \) liberates a gas during their reaction.

Key concepts

Gas Evolution

Gas evolution reactions are fascinating occurrences in chemistry where a gas is produced during a chemical reaction. This is typically observed when a chemical change causes certain substances to interact and generate gas products. During these reactions, discernable gas bubbles or emissions signal the transformation, marking a clear visual indication.
Common examples include reactions like the one between sodium hydroxide (\( \mathrm{NaOH} \)) and carbon (\( \mathrm{C} \)) which yield sodium carbonate (\( \mathrm{Na}_{2}\mathrm{CO}_{3} \)), water, and hydrogen gas (\( \mathrm{H}_2 \)). Hydrogen gas is released as a byproduct and can be observed as bubbling in the solution.

• Indicators: The presence of gas may produce bubbles or a characteristic fizz.
• Examples: Such reactions often involve acids with metals or carbonate reactions.

Understanding these reactions is crucial because they demonstrate exothermic processes producing energy and evolution of gas.

Reduction Reactions

Reduction reactions are essential parts of redox (reduction-oxidation) processes where an element gains electrons. Reduction always occurs alongside oxidation, where another element loses electrons.
In the specific reaction between magnesium (\( \mathrm{Mg} \)) and carbon dioxide (\( \mathrm{CO}_{2} \)), magnesium acts as a reducing agent. It transfers electrons to carbon dioxide, converting it into magnesium oxide (\( \mathrm{MgO} \)) and carbon (\( \mathrm{C} \)). Though this does not result in gas evolution, it's a classic example of reduction.

• Role of electron transfer: Reducing agents donate electrons while oxidizing agents accept them.
• Key components: Changes in oxidation states highlight transformation.

In learning reduction reactions, recognizing oxidizing and reducing agents simplifies predicting reaction outcomes.

Chemical Equations

Chemical equations are pivotal as they succinctly represent chemical reactions using symbols and formulas. They provide invaluable information about the reactants and products, and their stoichiometric relationships, illustrating how substances transform during reactions.
Consider the reaction where sodium hydroxide (\( \mathrm{NaOH} \)) and carbon (\( \mathrm{C} \)) combine: \[ 2\mathrm{NaOH} + 2\mathrm{C} \rightarrow \mathrm{Na}_{2}\mathrm{CO}_{3} + \mathrm{H}_{2}\] Here, balanced equations are key, showing equal atoms of each element.
The systematic arrangement conveys operational chemistry rules that govern reactant behavior for predicting outcomes:

• Reactants: The substances initially present, like \( \mathrm{NaOH} \) and \( \mathrm{C} \).
• Products: The new substances formed, i.e., \( \mathrm{Na}_{2}\mathrm{CO}_{3} \) and \( \mathrm{H}_2 \).

Ultimately, chemical equations are a universal language describing chemical transformations.

Reaction Analysis

Reaction analysis involves evaluating potential chemical processes to decipher the transformations occurring during reactions. This enables chemists to identify the types of reactions taking place and predict their products.
When analyzing reactions such as those between magnesium and boron (\( \mathrm{B}_{2} \mathrm{O}_{3} \)), or silicon dioxide (\( \mathrm{SiO}_{2} \)) and sodium (\( \mathrm{Na} \)), understanding the stability and nature of compounds is crucial.

• Outcome predictions: By understanding reactant properties, it's easier to anticipate reaction endings.
• Reaction conditions: Identifying necessary conditions for reactions to occur helps in avoiding non-reactions.

In learning how reactions proceed and under what circumstances they liberate gases or proceed without visible change, deeper comprehension of chemical interactions is achieved.