Consider the unbalanced redox reaction: Cr₂O₇^2-(aq) + Cu(s) → Cr³⁺(aq) + Cu²⁺(aq) Balance the equation and determine the volume of a 0.850 M K₂Cr₂O₇ solution required to completely react with 5.25 g of Cu.

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Identify the oxidation and reduction half-reactions. Chromium is reduced from Cr2O7^{2-} to Cr^{3+}, and copper is oxidized from Cu to Cu^{2+}.

Write the half-reactions: Reduction: Cr2O7^{2-} + 14H^+ + 6e^- -> 2Cr^{3+} + 7H2O. Oxidation: Cu -> Cu^{2+} + 2e^-.

Balance the electrons transferred in the half-reactions by multiplying the oxidation half-reaction by 3 and the reduction half-reaction by 1, then add them together.

Calculate the moles of Cu using its molar mass: moles of Cu = mass of Cu / molar mass of Cu.

Use stoichiometry to find the moles of K2Cr2O7 needed, then calculate the volume of the 0.850 M K2Cr2O7 solution using the formula: volume = moles / concentration.

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주요 개념

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Redox Reactions

Redox reactions involve the transfer of electrons between two species, where one species is oxidized (loses electrons) and the other is reduced (gains electrons). In this reaction, copper (Cu) is oxidized to Cu²⁺, while dichromate ions (Cr2O7²⁻) are reduced to Cr³⁺. Understanding the oxidation states and the electron transfer is crucial for balancing the reaction.

Balancing Chemical Equations

Balancing chemical equations ensures that the number of atoms for each element is the same on both sides of the equation, adhering to the law of conservation of mass. This involves adjusting coefficients in front of compounds to achieve balance, particularly in redox reactions where both oxidation and reduction half-reactions must be considered.

Molarity and Stoichiometry

Molarity (M) is a measure of concentration defined as moles of solute per liter of solution. Stoichiometry involves using the balanced chemical equation to relate the amounts of reactants and products. In this problem, calculating the moles of Cu from its mass and using the stoichiometric coefficients from the balanced equation will allow for determining the volume of the K2Cr2O7 solution needed for the reaction.

Consider the unbalanced redox reaction: Cr2O72-(aq) + Cu(s) → Cr3+(aq) + Cu2+(aq) Balance the equation and determine the volume of a 0.850 M K2Cr2O7 solution required to completely react with 5.25 g of Cu.