Question

Write equations for the reactions of (a) water with \(\mathrm{Ca}_{3} \mathrm{P}_{2}\) (b) aqueous \(\mathrm{NaOH}\) with \(\mathrm{NH}_{4} \mathrm{Cl}\); (c) aqueous \(\mathrm{NH}_{3}\) with \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2} ;(\mathrm{d}) \mathrm{AsH}_{3}\) with an excess of \(\mathrm{I}_{2}\) in neutral aqueous solution; (c) \(\mathrm{PH}_{3}\) with \(\mathrm{KNH}_{2}\) in liquid \(\mathrm{NH}_{3}\)

Short answer

Equations: (a) \(\mathrm{Ca}_{3}\mathrm{P}_{2} + 6\mathrm{H}_{2}\mathrm{O} \rightarrow 3\mathrm{Ca(OH)}_{2} + 2\mathrm{PH}_{3}\); (b) \(\mathrm{NaOH} + \mathrm{NH}_{4}\mathrm{Cl} \rightarrow \mathrm{NaCl} + \mathrm{H}_{2}\mathrm{O} + \mathrm{NH}_{3}\); (c) \(2\mathrm{NH}_{3} + \mathrm{Mg}(\mathrm{NO}_{3})_{2} + 2\mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{Mg(OH)}_{2} + 2\mathrm{NH}_{4}\mathrm{NO}_{3}\); (d) \(\mathrm{AsH}_{3} + 3\mathrm{I}_{2} \rightarrow \mathrm{AsI}_{3} + 3\mathrm{HI}\); (e) \(2\mathrm{PH}_{3} + 2\mathrm{KNH}_{2} \rightarrow \mathrm{P}_{2}\mathrm{H}_{4} + 2\mathrm{KSH}\).

Step-by-step solution

Reaction of Water with Calcium Phosphide

When water reacts with calcium phosphide, it produces calcium hydroxide and phosphine gas. The chemical equation for this reaction is: \[ \mathrm{Ca}_{3}\mathrm{P}_{2} + 6\mathrm{H}_{2}\mathrm{O} \rightarrow 3\mathrm{Ca(OH)}_{2} + 2\mathrm{PH}_{3} \]

Reaction of NaOH with NH4Cl

Aqueous sodium hydroxide reacts with ammonium chloride to produce sodium chloride, water, and ammonia gas. The balanced chemical equation for this reaction is: \[ \mathrm{NaOH} + \mathrm{NH}_{4}\mathrm{Cl} \rightarrow \mathrm{NaCl} + \mathrm{H}_2\mathrm{O} + \mathrm{NH}_3 \]

Reaction of Aqueous NH3 with Magnesium Nitrate

Aqueous ammonia reacts with magnesium nitrate to produce magnesium hydroxide and ammonium nitrate. The chemical equation is given by: \[ 2\mathrm{NH}_{3} + \mathrm{Mg}(\mathrm{NO}_{3})_{2} + 2\mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{Mg(OH)}_{2} + 2\mathrm{NH}_{4}\mathrm{NO}_{3} \]

Reaction of Arsine with Iodine

Arsine \((\mathrm{AsH}_{3})\) reacts with iodine in a neutral aqueous solution to form arsenic triiodide and hydrogen iodide. The balanced equation is: \[ \mathrm{AsH}_{3} + 3\mathrm{I}_{2} \rightarrow \mathrm{AsI}_{3} + 3\mathrm{HI} \]

Reaction of Phosphine with Potassium Amide

In liquid ammonia, phosphine reacts with potassium amide to produce diphosphine and potassium sulfide: \[ 2\mathrm{PH}_{3} + 2\mathrm{KNH}_{2} \rightarrow \mathrm{P}_{2}\mathrm{H}_{4} + 2\mathrm{KSH} \]

Key concepts

Chemical Equations

Chemical equations are the symbolic representations of chemical reactions. They illustrate how reactants transform into products by rearranging their atoms.
A balanced chemical equation has the same number of each type of atom on both sides, respecting the law of conservation of mass. This ensures that no atoms are created or destroyed in the process.
Understanding chemical equations is essential in predicting the outcomes of reactions, calculating reactants or products, and understanding the nature of the substances involved.

• Reactants are the starting materials in a chemical reaction.
• Products are the substances formed as a result of a chemical reaction.
• Coefficients are the numbers in front of the chemical formulas, indicating how many molecules or moles of each substance are involved.

Balancing chemical equations involves adjusting these coefficients so that the number of each type of atom is equal on both sides. This is a crucial skill for accurately representing chemical reactions.

Calcium Phosphide Reactions

Calcium phosphide (\(\mathrm{Ca}_3\mathrm{P}_2\)) is a compound that reacts with water to produce phosphine gas (\(\mathrm{PH}_3\) ) and calcium hydroxide. This reaction is highly exothermic, meaning it releases a significant amount of heat.
The balanced chemical equation for this reaction is:\[ \mathrm{Ca}_3\mathrm{P}_2 + 6\mathrm{H}_2\mathrm{O} \rightarrow 3\mathrm{Ca(OH)}_2 + 2\mathrm{PH}_3 \]
Phosphine gas is a toxic, flammable gas with a garlic-like odor, often used in pesticides and fumigants.
Calcium hydroxide is a caustic substance used in plaster and water treatment.

• When using calcium phosphide, handle it carefully to avoid uncontrolled release of phosphine.
• Ensure proper ventilation when conducting reactions involving phosphine gas.

Ammonium Chloride Reactions

Ammonium chloride (\(\mathrm{NH}_4\mathrm{Cl}\) ) reacts with sodium hydroxide (\(\mathrm{NaOH}\) ) to produce ammonia gas, water, and sodium chloride. The balanced chemical equation for this reaction is:\[ \mathrm{NaOH} + \mathrm{NH}_4\mathrm{Cl} \rightarrow \mathrm{NaCl} + \mathrm{H}_2\mathrm{O} + \mathrm{NH}_3 \]
This reaction is often used in labs to generate ammonia gas. Ammonia is known for its pungent smell and is widely used in cleaning products, fertilizers, and as a refrigerant.
Sodium chloride, commonly known as table salt, is essential for human nutrition and a common household compound.

• When performing this reaction, always work in a well-ventilated area to avoid ammonia inhalation.
• Ammonium chloride can also be used to buffer solutions due to its weak acidic properties.

Aqueous Ammonia Reactions

Aqueous ammonia, a solution of ammonia in water, reacts with magnesium nitrate (\(\mathrm{Mg(NO}_3 ext{)}_2\) ) to produce magnesium hydroxide and ammonium nitrate. This reaction proceeds with the following chemical equation:\[ 2\mathrm{NH}_3 + \mathrm{Mg(NO}_3 ext{)}_2 + 2\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Mg(OH)}_2 + 2\mathrm{NH}_4\mathrm{NO}_3 \]
Magnesium hydroxide is an insoluble substance, often appearing as a white precipitate. It is used in antacids and laxatives.
Ammonium nitrate is a well-known nitrogen source in fertilizers and a component used in explosives.

• The reaction is essential for understanding precipitation reactions, where an insoluble solid forms from soluble reactants.
• Ammonia in water acts as a weak base and can be crucial in altering pH levels in various solutions.