Ch.4 - Reactions in Aqueous Solution

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McMurry 8th Edition

Ch.4 - Reactions in Aqueous Solution

Problema 163

Capitolo 4, Problema 163

Gold metal is extracted from its ore by treating the crushed rock with an aerated cyanide solution. The unbalanced equation for the reaction is (a) Balance the equation for this reaction in basic solution.

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Identify the unbalanced chemical equation for the reaction. Typically, the reaction involves gold (Au), cyanide ions (CN^-), oxygen (O_2), and water (H_2O) to form a gold-cyanide complex and hydroxide ions (OH^-).

Write the half-reactions for the oxidation and reduction processes. In this case, gold is oxidized, and oxygen is reduced.

Balance each half-reaction separately. Start by balancing the atoms other than O and H, then balance the oxygen atoms by adding H_2O, and balance the hydrogen atoms by adding H^+.

Since the reaction occurs in a basic solution, add OH^- to both sides of the equation to neutralize the H^+ ions, forming water. Simplify the equation by canceling out water molecules if necessary.

Combine the balanced half-reactions, ensuring that the electrons are canceled out, to obtain the balanced overall equation for the reaction in basic solution.

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Balancing Chemical Equations

Balancing chemical equations involves ensuring that the number of atoms for each element is the same on both sides of the equation. This is crucial for obeying the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. Balancing can be achieved by adjusting coefficients in front of the chemical formulas.

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01:32

Balancing Chemical Equations

Redox Reactions

Redox (reduction-oxidation) reactions involve the transfer of electrons between species, resulting in changes in oxidation states. In the context of gold extraction, cyanide acts as a ligand that forms complexes with gold ions, and understanding the oxidation states of gold and cyanide is essential for balancing the reaction correctly. Identifying which species are oxidized and reduced is key to writing a balanced equation.

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Identifying Redox Reactions

Basic Solution Conditions

In basic solution conditions, hydroxide ions (OH-) are present, which can affect the balancing of redox reactions. When balancing equations in basic solutions, it is often necessary to add water molecules and hydroxide ions to both sides of the equation to account for the basic environment. This step is crucial for achieving a balanced equation that accurately reflects the reaction conditions.

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01:04

Balancing Basic Redox Reactions

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Domanda del libro di testo

On heating a 0.200 g sample of a certain semimetal M in air, the corresponding oxide M2O3 was obtained. When the oxide was dissolved in aqueous acid and titrated with KMnO4, 10.7 mL of 0.100 M MnO4- was required for complete reac-tion. The unbalanced equation is (a) Balance the equation.

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Domanda del libro di testo

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Domanda del libro di testo

On heating a 0.200 g sample of a certain semimetal M in air, the corresponding oxide M2O3 was obtained. When the oxide was dissolved in aqueous acid and titrated with KMnO4, 10.7 mL of 0.100 M MnO4- was required for complete reac- tion. The unbalanced equation is X (b) How many moles of oxide were formed, and how many moles of semimetal were in the initial 0.200 g sample?

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