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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 92d

The accompanying photo shows the reaction between a solution of Cd(NO3)2 and one of Na2S. (d) Is this a redox reaction?

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Identify the reactants and products in the reaction: Cd(NO_3)_2 and Na_2S react to form CdS and NaNO_3.
Determine the oxidation states of each element in the reactants and products. For example, in Cd(NO_3)_2, Cd is +2 and in Na_2S, S is -2.
Check if there is a change in oxidation states for any of the elements from reactants to products. In CdS, Cd is still +2 and S is still -2, indicating no change.
Since there is no change in oxidation states, this indicates that no electrons are transferred between the elements.
Conclude that the reaction is not a redox reaction, as there is no change in oxidation states of the elements involved.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Redox Reactions

Redox reactions, or reduction-oxidation reactions, involve the transfer of electrons between two species. In these reactions, one substance is oxidized (loses electrons) while another is reduced (gains electrons). Identifying whether a reaction is a redox process requires analyzing the oxidation states of the elements involved before and after the reaction.
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Oxidation States

Oxidation states (or oxidation numbers) are a way to keep track of electrons in chemical reactions. They indicate the degree of oxidation of an atom in a compound, helping to determine whether an atom has gained or lost electrons. In the context of the given reaction, calculating the oxidation states of cadmium (Cd) and sulfur (S) will clarify if any changes occur, indicating a redox reaction.
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Ionic Compounds and Solubility

Ionic compounds, such as Cd(NO3)2 and Na2S, dissociate into their constituent ions when dissolved in water. Understanding the solubility of these compounds is crucial, as it affects the reaction dynamics. The formation of precipitates or soluble ions can influence whether a redox reaction occurs, as the physical state of the reactants can determine the pathway of the reaction.
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Related Practice
Textbook Question

A 1.248-g sample of limestone rock is pulverized and then treated with 30.00 mL of 1.035 M HCl solution. The excess acid then requires 11.56 mL of 1.010 M NaOH for neutralization. Calculate the percentage by mass of calcium carbonate in the rock, assuming that it is the only substance reacting with the HCl solution.

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Textbook Question

Uranium hexafluoride, UF6, is processed to produce fuel for nuclear reactors and nuclear weapons. UF6 can be produced in a two-step reaction. Solid uranium (IV) oxide, UO2, is first made to react with hydrofluoric acid (HF) solution to form solid UF4 with water as a by-product. UF4 further reacts with fluorine gas to form UF6. (a) Write the balanced molecular equations for the conversion of UO2 into UF4 and the conversion of UF4 to UF6. (b) Which step is an acid-base reaction?

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Textbook Question

The accompanying photo shows the reaction between a solution of Cd(NO3)2 and one of Na2S. (b) What ions remain in solution?

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Open Question
Suppose you have a solution that might contain any or all of the following cations: Ni2+, Ag+, Sr2+, and Mn2+. Addition of HCl solution causes a precipitate to form. After filtering off the precipitate, H2SO4 solution is added to the resulting solution and another precipitate forms. This is filtered off, and a solution of NaOH is added to the resulting solution. No precipitate is observed. Which of the four ions listed above must be absent from the original solution?
Open Question
You choose to investigate some of the solubility guidelines for two ions not listed in Table 4.1, the chromate ion (CrO₄²⁻) and the oxalate ion (C₂O₄²⁻). You are given 0.01 M solutions (A, B, C, D) of four water-soluble salts: When these solutions are mixed, the following observations are made:
(a) Write a net ionic equation for the reaction that occurs in the first experiment. (b) Identify the precipitate formed in the first experiment. (c) Write a net ionic equation for the reaction that occurs in the third experiment. (d) Identify the precipitate formed in the third experiment. (e) Write a net ionic equation for the reaction that occurs in the fourth experiment. (f) Identify the precipitate formed in the fourth experiment. (g) Write a net ionic equation for the reaction that occurs in the fifth experiment. (h) Identify the precipitate formed in the fifth experiment. (i) Write a net ionic equation for the reaction that occurs in the sixth experiment. (j) Identify the precipitate formed in the sixth experiment.
Textbook Question

Antacids are often used to relieve pain and promote healing in the treatment of mild ulcers. Write balanced net ionic equations for the reactions between the aqueous HCl in the stomach and each of the following substances used in various antacids: (d) NaAl1CO3)1OH221s2

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