Problem 104 - General Chemistry

Question

Describe in words how you would do each of the following preparations. Then give the molecular equation for each preparation. a. \(\mathrm{MgCl}_{2}(s)\) from \(\mathrm{MgCO}_{3}(s)\) b. \(\mathrm{NaNO}_{3}(s)\) from \(\mathrm{NaCl}(s)\) c. \(\mathrm{Al}(\mathrm{OH})_{3}(s)\) from \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}(s)\) d. \(\mathrm{HCl}(a q)\) from \(\mathrm{H}_{2} \mathrm{SO}_{4}(a q)\)

Step-by-Step Solution

Answer

React MgCO3 with HCl, NaCl with HNO3, Al(NO3)3 with NaOH, and NaCl with H2SO4 for respective preparations.

Step 1: Preparation of MgCl2 from MgCO3

To prepare magnesium chloride ( \( \mathrm{MgCl}_{2}(s) \) ) from magnesium carbonate ( \( \mathrm{MgCO}_{3}(s) \) ), you'll need to react magnesium carbonate with hydrochloric acid. Begin by dissolving \( \mathrm{MgCO}_{3}(s) \) in \( \mathrm{HCl}(aq) \) , which will produce \( \mathrm{MgCl}_{2}(aq) \) and \( \mathrm{CO}_{2}(g) \) gas, and water. The resulting solution can be evaporated to obtain solid \( \mathrm{MgCl}_{2}(s) \). The molecular equation for this reaction is: \[ \mathrm{MgCO}_{3}(s) + 2\mathrm{HCl}(aq) \rightarrow \mathrm{MgCl}_{2}(aq) + \mathrm{CO}_{2}(g) + \mathrm{H}_{2}\mathrm{O}(l) \]

Step 2: Preparation of NaNO3 from NaCl

To obtain sodium nitrate ( \( \mathrm{NaNO}_{3}(s) \) ) from sodium chloride ( \( \mathrm{NaCl}(s) \) ), use nitric acid. React \( \mathrm{NaCl}(s) \) with \( \mathrm{HNO}_{3}(aq) \), producing \( \mathrm{NaNO}_{3}(aq) \) and releasing \( \mathrm{HCl}(g) \). The solid \( \mathrm{NaNO}_{3}(s) \) can be collected by evaporating the water from the solution. The molecular equation is: \[ \mathrm{NaCl}(s) + \mathrm{HNO}_{3}(aq) \rightarrow \mathrm{NaNO}_{3}(aq) + \mathrm{HCl}(g) \]

Step 3: Preparation of Al(OH)3 from Al(NO3)3

To form aluminum hydroxide ( \( \mathrm{Al(OH)}_{3}(s) \) ) from aluminum nitrate ( \( \mathrm{Al(NO}_{3})_{3}(s) \) ), an aluminum salt solution is treated with a strong base such as sodium hydroxide ( \( \mathrm{NaOH}(aq) \) ). The reaction produces \( \mathrm{Al(OH)}_{3}(s) \) and sodium nitrate ( \( \mathrm{NaNO}_{3}(aq) \) ). The equation is: \[ \mathrm{Al(NO}_{3})_{3}(aq) + 3\mathrm{NaOH}(aq) \rightarrow \mathrm{Al(OH)}_{3}(s) + 3\mathrm{NaNO}_{3}(aq) \]

Step 4: Preparation of HCl from H2SO4

To produce hydrochloric acid ( \( \mathrm{HCl}(aq) \) ) from sulfuric acid ( \( \mathrm{H}_{2} \mathrm{SO}_{4}(aq) \)), treat it with sodium chloride ( \( \mathrm{NaCl}(s) \) ). The reaction releases \( \mathrm{HCl}(g) \), which can be dissolved in water to obtain \( \mathrm{HCl}(aq) \), and also produces sodium bisulfate ( \( \mathrm{NaHSO}_{4}(s) \) ): \[ \mathrm{NaCl}(s) + \mathrm{H}_{2} \mathrm{SO}_{4}(aq) \rightarrow \mathrm{HCl}(g) + \mathrm{NaHSO}_{4}(s) \]

Key Concepts

Molecular Equation

In chemistry, a molecular equation represents compounds as individual molecules in a chemical reaction. It is an essential tool used to understand how reactants transform into products. Molecular equations provide a clear picture of the substances involved in a reaction by specifying their physical states, such as solid, liquid, gas, or aqueous (dissolved in water). This notation helps chemists predict the outcomes of reactions and the relationships between different compounds. For instance, a simple reaction such as the conversion of magnesium carbonate to magnesium chloride can be represented as:\[ \mathrm{MgCO}_{3}(s) + 2\,\mathrm{HCl}(aq) \rightarrow \mathrm{MgCl}_{2}(aq) + \mathrm{CO}_{2}(g) + \mathrm{H}_{2}\mathrm{O}(l) \]This equation shows all involved molecules and the resulting products, providing a comprehensive understanding of the chemical change.

Acid-Base Reactions

Acid-base reactions are chemical reactions that occur between acids and bases. These reactions often result in the formation of water and a salt. They are a fundamental part of chemistry due to their wide occurrence and application.Basic Concepts:

• Acids: Substances that donate protons (H⁺) in a reaction. For example, hydrochloric acid (HCl) and sulfuric acid (H₂SO₄).
• Bases: Substances that accept protons, often hydroxide (OH^-) ions like sodium hydroxide (NaOH).

In a typical acid-base reaction, an acid reacts with a base to produce water and a salt. For example, when sodium hydroxide reacts with aluminum nitrate, it forms aluminum hydroxide and sodium nitrate:\[ \mathrm{Al(NO}_{3})_{3}(aq) + 3\,\mathrm{NaOH}(aq) \rightarrow \mathrm{Al(OH)}_{3}(s) + 3\,\mathrm{NaNO}_{3}(aq) \]This illustrates the transformation of the starting compounds into new substances, highlighting the important role of acid-base reactions in chemical processes.

Precipitation Reactions

Precipitation reactions occur when two solutions react to form an insoluble solid, called a precipitate. These reactions are essential for purifying substances and in analytical chemistry to identify ions present in a solution.Understanding Precipitation:

• The solid that forms falls out of solution, and this solid can often be seen as a cloudiness or a sediment at the bottom of the container.
• Not all ionic compounds will form a precipitate; solubility rules help predict whether a solid will form.

An example of precipitation is when aluminum nitrate reacts with sodium hydroxide to form aluminum hydroxide, which is insoluble in water. This is described by the following equation:\[ \mathrm{Al(NO}_{3})_{3}(aq) + 3\,\mathrm{NaOH}(aq) \rightarrow \mathrm{Al(OH)}_{3}(s) + 3\,\mathrm{NaNO}_{3}(aq) \]Here, aluminum hydroxide is the precipitate, demonstrating how such reactions can help isolate specific compounds from mixtures.

Solubility

Solubility refers to the ability of a substance to dissolve in a solvent, such as water. It plays a crucial role in determining whether a chemical reaction will proceed in solution.Factors Affecting Solubility:

• Temperature: Generally, solubility increases with temperature, although this is not always true for all substances.
• Nature of the solvent and solute: Polar substances dissolve in polar solvents, while non-polar substances dissolve in non-polar solvents.

Understanding solubility allows chemists to predict reaction outcomes and perform chemical separations. For example, in the preparation of sodium nitrate from sodium chloride, the solubility of the reactant and product in water facilitates the separation and collection of the desired sodium nitrate solid:\[ \mathrm{NaCl}(s) + \mathrm{HNO}_{3}(aq) \rightarrow \mathrm{NaNO}_{3}(aq) + \mathrm{HCl}(g) \]By evaporating water from the sodium nitrate solution, a solid product is formed. This example clearly illustrates the pivotal role of solubility in chemical reactions and preparations.

Chemical Preparation Processes

Chemical preparation processes involve transforming substances from one form to another through a series of chemical reactions. These processes are crucial for producing desired chemicals in industry and research settings.In chemical preparation, reactions are carefully planned and executed to ensure high yield and purity of the final product. For instance, preparing hydrochloric acid from sulfuric acid involves a careful reaction with sodium chloride:\[ \mathrm{NaCl}(s) + \mathrm{H}_{2}\mathrm{SO}_{4}(aq) \rightarrow \mathrm{HCl}(g) + \mathrm{NaHSO}_{4}(s) \]The setup often requires specific conditions like the right temperature, concentration, and time to ensure complete transformation.Important Considerations:

• Selection of reactants: Based on their cost, availability, and chemical properties.
• Handling of by-products: Proper methods to manage or utilize any side products generated during the reaction.

These processes underpin the synthesis of countless everyday products and highlight the importance of understanding chemical reactions and properties in real-world applications.