Problem 50 - General Chemistry: Principles and Modern Applications

Question

Write plausible chemical equations for preparing each compound from the indicated starting material: (a) \(\operatorname{SnCl}_{2}\) from \(\operatorname{SnO} ;\) (b) \(\operatorname{SnCl}_{4}\) from \(\operatorname{Sn} ;\) (c) \(\operatorname{PbCrO}_{4}\) from \(\mathrm{PbO}_{2}\). What reagents (acids, bases, salts) and equipment commonly available in the laboratory are needed for each reaction?

Step-by-Step Solution

Answer

The reactions, (a) \(\operatorname{SnO} + 2\operatorname{HCl} \rightarrow \operatorname{SnCl}_{2} + \operatorname{H}_{2}\operatorname{O}\), (b) \(\operatorname{Sn} + 4\operatorname{HCl} + catalyst \rightarrow \(\operatorname{SnCl}_{4} + 2\operatorname{H}_{2}\), and (c) \(\operatorname{PbO}_{2} + \operatorname{ K}_{2}\operatorname{CrO}_{4}\rightarrow \operatorname{PbCrO}_{4} + 2\operatorname{K}^{+} \operatorname{O}^{2-}\) show how each respective compound can be prepared from the starting material.

Step 1: Preparing SnCl2 from SnO

To obtain \(\operatorname{SnCl}_{2}\) from \(\operatorname{SnO}\), react \(\operatorname{SnO}\) with \(2\operatorname{HCl}\) where \(HCl\) is Hydrochloric acid. The reaction is: \(\operatorname{SnO} + 2\operatorname{HCl} \rightarrow \operatorname{SnCl}_{2} + \operatorname{H}_{2}\operatorname{O}\)

Step 2: Preparing SnCl4 from Sn

To obtain \(\operatorname{SnCl}_{4}\) from \(\operatorname{Sn}\), react \(\operatorname{Sn}\) with \(4\operatorname{HCl}\). This reaction requires a catalyst to speed up: the Chlorination reaction. The reaction is: \(\operatorname{Sn} + 4\operatorname{HCl} \rightarrow \(\operatorname{SnCl}_{4} + 2\operatorname{H}_{2}\)

Step 3: Preparing PbCrO4 from PbO2

Getting \(\operatorname{PbCrO}_{4}\) from \(\operatorname{PbO}_{2}\) involves adding \(\operatorname{PbO}_{2}\) to a solution of \( \operatorname{ K}_{2}\operatorname{CrO}_{4}\)(Potassium Chromate). The reaction is: \(\operatorname{PbO}_{2} + \operatorname{ K}_{2}\operatorname{CrO}_{4}\rightarrow \operatorname{PbCrO}_{4} + 2\operatorname{K}^{+} \operatorname{O}^{2-}\)

Key Concepts

Chemical Equation

Understanding chemical equations is essential in chemistry. A chemical equation represents a chemical reaction where the reactants are transformed into products.
Each reactant and product is represented by its chemical formula, and these equations must be balanced to show the same number of each type of atom on both sides.

The three reactions in the exercise showcase different scenarios:

• SnO reacting with HCl to produce SnCl₂ and water.
• Sn reacting with HCl to form SnCl₄ and hydrogen.
• PbO₂ interacting with K₂CrO₄ to yield PbCrO₄.

Balancing these equations ensures that the law of conservation of mass is upheld, meaning atoms are neither created nor destroyed in the reaction.
This highlights how important chemical equations are for predicting the quantities of products formed.

Laboratory Reagents

Laboratory reagents are the substances used to bring about a reaction in experiments. They are crucial for performing the chemical transformations needed in various equations.
In the given reactions, typical lab reagents include:

• Hydrochloric Acid (HCl): Used in the first two reactions to provide chloride ions for forming tin chloride.
• Potassium Chromate (K₂CrO₄): Utilized in the third equation to react with PbO₂.

These reagents are chosen based on their ability to efficiently drive the desired chemical reaction under controlled conditions.
Understanding the role and nature of these reagents helps ensure successful and safe lab work.

Inorganic Chemistry

Inorganic chemistry focuses on compounds that are not based on carbon-hydrogen bonds. It includes the study of metals, minerals, and organometallic compounds.

Our exercise involves inorganic compounds like SnO, SnCl₂, SnCl₄, PbO₂, and K₂CrO₄.
These compounds demonstrate:

• The behavior of metals like Tin (Sn) and Lead (Pb) when reacting with non-metals and other inorganics.
• The formation of salts and oxides, key themes in inorganic chemistry.

Understanding inorganic reactions is key for applications in materials science, metallurgy, and catalysis.

Reaction Mechanisms

Reaction mechanisms describe the individual steps that occur during a chemical reaction.
Detailed mechanisms help explain how reactants turn into products, involving intermediates, transition states, and energy changes.

In the exercise:

• Sn reacting with HCl: Likely involves multiple steps, including electron transfer and formation of hydrogen gas.
• PbO₂ with K₂CrO₄: May involve redox reactions where electrons are exchanged between ions, leading to the formation of complex compounds like PbCrO₄.

Understanding these steps helps chemists control reactions and optimize conditions for desired products, highlighting the importance of reaction mechanisms in chemistry.