Problem 33 - General Chemistry: Principles and Modern Applications

Question

In the purification of bauxite ore, a preliminary step in the production of aluminum, \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})\) can be converted to \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})\) by passing \(\mathrm{CO}_{2}(\mathrm{g})\) through the solution. Write an equation for the reaction that occurs. Could HCl(aq) be used instead of \(\mathrm{CO}_{2}(\mathrm{g}) ?\) Explain.

Step-by-Step Solution

Answer

Balanced chemical equation: \[ \mathrm{CO}_{2}(\mathrm{g}) + \left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq}) \rightarrow \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}) + \mathrm{H}_{2}\mathrm{O}(\mathrm{l}) + \mathrm{CO}_{3}^{2-} (\mathrm{aq}). \(\mathrm{HCl}(\mathrm{aq})\) could be used as a substitute for \(\mathrm{CO}_{2}(\mathrm{g})\), but it may affect the overall process due to changes in pH and other properties.

Step 1: Write and Balance the Chemical Equation

Convert \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})\) into \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})\) using \(\mathrm{CO}_{2}(\mathrm{g})\). The balanced chemical equation for this is: \[ \mathrm{CO}_{2}(\mathrm{g}) + \left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq}) \rightarrow \mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}) + \mathrm{H}_{2}\mathrm{O}(\mathrm{l}) + \mathrm{CO}_{3}^{2-} (\mathrm{aq})\] The reaction implies that the \(\mathrm{CO}_{2}(\mathrm{g})\) provides \(\mathrm{H}^{+}\) ions which combines with the OH groups of \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})\) to form \(\mathrm{H}_{2}\mathrm{O}(\mathrm{l})\) and \(\mathrm{CO}_{3}^{2-} (\mathrm{aq})\), leaving behind \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}).\)

Step 2: Understanding if \(\mathrm{HCl}(\mathrm{aq})\) could be used as a substitute for \(\mathrm{CO}_{2}(\mathrm{g})\)

\(\mathrm{HCl}(\mathrm{aq})\) could be used as a substitute for \(\mathrm{CO}_{2}(\mathrm{g})\) as it would also provide H^+ ions to combine with the OH groups of \(\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})\) to form \(\mathrm{H}_{2}\mathrm{O}(\mathrm{l})\), leaving behind \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})\) and \(\mathrm{Cl}^{-} (\mathrm{aq})\) . It should however be noted that this might change the pH and other properties of the resulting solution, and may also affect the overall process of bauxite purification, depending on the specific industrial process used.

Key Concepts

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into different substances. In the context of bauxite purification, these reactions are vital because they allow us to produce aluminum. Key players in these reactions are reactants and products. Here, reactants such as \( \mathrm{CO}_{2}(\mathrm{g}) \) and \( \left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq}) \) interact to form new products like \( \mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}) \).

The chosen reactant \( \mathrm{CO}_{2}(\mathrm{g}) \) helps in the conversion process by breaking down the original compound. When \( \mathrm{CO}_{2} \) is passed through the solution, it facilitates the formation of water and carbonate ions, leaving a solid which can be further processed to aluminum. Reactants and products in this chemical reaction interact with each other to transform the materials from a solution form into a solid state.

Aluminum Production

Producing aluminum from bauxite is a complex process involving multiple stages, with purification being a critical step. Bauxite is an ore that contains a mixture of minerals; hence it needs to be purified to obtain aluminum. The conversion of \( \left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq}) \) to a solid form \( \mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}) \) is a significant part of this purification process. This solid can then be dried and further processed to extract pure aluminum.

During the purification, the use of gases like \( \mathrm{CO}_{2} \) helps to transform the soluble aluminum hydroxide present in the ore into an insoluble form. This separation from the liquid solution aids in the removal of impurities, thereby enriching the aluminum content. - The process needs to ensure the balance between cost-effectiveness and efficiency. - The direct production of high-purity aluminum depends heavily on the efficiency of these chemical reactions, making the consideration of alternative reactants significant.The choice of reactants and process controls, such as pH and temperature, can vastly impact the quality and quantity of aluminum extracted.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They allow us to predict the results of reactions under given conditions. The equation: \[ \mathrm{CO}_{2}(\mathrm{g}) + \left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq}) \rightarrow \mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}) + \mathrm{H}_{2}\mathrm{O}(\mathrm{l}) + \mathrm{CO}_{3}^{2-} (\mathrm{aq}) \]illustrates how reactants transform into products in the process of bauxite purification.

Rearranging or substituting reactants, such as opting for \( \mathrm{HCl} \) instead of \( \mathrm{CO}_{2} \), will change the chemical equation. This change might result in different by-products and solution properties.

• It is essential to balance these equations to follow the conservation of mass and elemental charges.
• Understanding these equations helps industries optimize the extraction process, manage waste, and ensure a sustainable production system.

Each term and symbol in the equation plays a crucial role in understanding how substances interact and what outcomes can be expected from these reactions.