Problem 17 - Chemistry The Central Science

Question

Complete and balance the following equations: $$\begin{array}{l}{\text { (a) } \mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow} \\ {\text { (b) } \mathrm{CuO}(s)+\mathrm{HNO}_{3}(a q) \longrightarrow} \\ {\text { (c) } \mathrm{WO}_{3}(s)+\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow}}\end{array}$$ $$\begin{array}{l}{\text { (d) } \mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow} \\ {\text { (e) } \mathrm{Al}_{4} \mathrm{C}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow}\end{array}$$

Step-by-Step Solution

Answer

The short answer to the question is: (a) $$\mathrm{NaOCH}_{3}(s) + \mathrm{H}_{2}\mathrm{O}(l) \longrightarrow \mathrm{NaOH}(aq) +\mathrm{CH}_{3}\mathrm{OH}(l)$$ (b) $$\mathrm{CuO}(s) + 2 \mathrm{HNO}_{3}(aq) \longrightarrow \mathrm{Cu(NO}_{3})_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l)$$ (c) $$\mathrm{WO}_{3}(s) + 3 \mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{W}(s) + 3 \mathrm{H}_{2}\mathrm{O}(g)$$ (d) $$\mathrm{2NH}_{2}\mathrm{OH}(l) + \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{N}_{2}(g)$$ (e) $$\mathrm{Al}_{4} \mathrm{C}_{3}(s) + 12 \mathrm{H}_{2}\mathrm{O}(l) \longrightarrow 4 \mathrm{Al(OH)}_{3}(s) + 3 \mathrm{CH}_{4}(g)$$

Step 1: (a) Identifying Products and Balancing the Equation

(a) We have a reaction between sodium methoxide (NaOCH3) and water (H2O). This is a type of acid-base reaction, where the methoxide ion (OCH3⁻) will act as a base and water (H2O) as an acid. The products will be sodium hydroxide (NaOH) and methanol (CH3OH). The balanced equation is: $$\mathrm{NaOCH}_{3}(s) + \mathrm{H}_{2}\mathrm{O}(l) \longrightarrow \mathrm{NaOH}(aq) +\mathrm{CH}_{3}\mathrm{OH}(l).$$

Step 2: (b) Identifying Products and Balancing the Equation

(b) The reaction of copper(II) oxide (CuO) with nitric acid (HNO3) will produce copper(II) nitrate (Cu(NO3)2) and water (H2O) because it is an acid-base reaction. The balanced equation is: $$\mathrm{CuO}(s) + 2 \mathrm{HNO}_{3}(aq) \longrightarrow \mathrm{Cu(NO}_{3})_{2}(aq) + \mathrm{H}_{2}\mathrm{O}(l).$$

Step 3: (c) Identifying Products and Balancing the Equation

(c) Tungsten trioxide (WO3) reacting with hydrogen gas (H2) under heat (indicated by Δ) will produce tungsten metal (W) and water (H2O). This is a reduction reaction, as hydrogen reduces the tungsten oxide. The balanced equation is: $$\mathrm{WO}_{3}(s) + 3 \mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{W}(s) + 3 \mathrm{H}_{2}\mathrm{O}(g).$$

Step 4: (d) Identifying Products and Balancing the Equation

(d) When hydroxylamine (NH2OH) reacts with oxygen gas (O2), it will produce water (H2O) and nitrogen gas (N2) as products. The balanced equation is: $$\mathrm{2NH}_{2}\mathrm{OH}(l) + \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{N}_{2}(g).$$

Step 5: (e) Identifying Products and Balancing the Equation

(e) Aluminum carbide (Al4C3) reacting with water (H2O) will produce aluminum hydroxide (Al(OH)3) and methane gas (CH4) because it is a hydrolysis reaction. The balanced equation is: $$\mathrm{Al}_{4} \mathrm{C}_{3}(s) + 12 \mathrm{H}_{2}\mathrm{O}(l) \longrightarrow 4 \mathrm{Al(OH)}_{3}(s) + 3 \mathrm{CH}_{4}(g).$$

Key Concepts

Acid-Base Reactions

Acid-base reactions are a fundamental part of chemistry where an acid and a base react to form water and a salt. In the example given, sodium methoxide (\( \text{NaOCH}_3 \)) acts as the base, while water (\( \text{H}_2\text{O} \)) serves as the acid. This results in the formation of sodium hydroxide (\( \text{NaOH} \)), a base, and methanol (\( \text{CH}_3\text{OH} \)), an alcohol. This type of reaction is also known as a neutralization reaction.

• Acids are proton donors in such reactions.
• Bases are proton acceptors.
• Water, in many reactions, can act as either an acid or a base, depending on the circumstance.

Understanding the role of each reactant can help predict the products in these reactions and balance the equations effectively.

Reduction Reactions

Reduction reactions involve the gain of electrons by a substance. In the case of the reaction between tungsten trioxide (\( \text{WO}_3 \)) and hydrogen gas (\( \text{H}_2 \)), tungsten is reduced to its metallic state, while hydrogen acts as the reducing agent by donating electrons.

• Reduction refers to the gain of electrons or decrease in oxidation state.
• This process often releases energy.
• Reduction reactions are crucial in processes like metallurgy to extract metals from their ores.

Balancing these reactions requires attention to both the transfer of electrons and the conservation of mass across the reaction.

Hydrolysis Reactions

Hydrolysis reactions involve the chemical breakdown of a compound due to reaction with water. A classic example here is the reaction of aluminum carbide (\( \text{Al}_4\text{C}_3 \)), with water to produce aluminum hydroxide (\( \text{Al(OH)}_3 \)) and methane (\( \text{CH}_4 \)).

• Hydrolysis literally means "water splitting".
• Water plays a key role, acting as a reactant rather than a catalyst.
• These reactions are vital for biological processes, like digestion and metabolism.

By breaking bonds in compounds, hydrolysis changes large molecules into more manageable forms, effectively decomposing them.

Chemical Reactivity

Chemical reactivity refers to the propensity of a substance to engage in a chemical reaction. It indicates how easily and quickly a substance can transform into a new compound. Several factors affect chemical reactivity:

• Element type and position in the periodic table can denote reactivity levels.
• Temperature and pressure conditions influence the speed and extent of reactions.
• Catalysts and inhibitors can significantly alter the rate of a reaction.

The reaction of hydroxylamine (\( \text{NH}_2\text{OH} \)) with oxygen showcases chemical reactivity as the substances combine to form nitrogen and water, displaying how some compounds are more willing to transform under the right conditions. Understanding reactivity helps predict chemical behavior and design experiments accordingly.