Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 18: Problem 123

A piece of magnesium ribbon and a copper wire are partially immersed in a \(0.1 M \mathrm{HCl}\) solution in a beaker. The metals are joined externally by another piece of metal wire. Bubbles are seen to evolve at both the \(\mathrm{Mg}\) and \(\mathrm{Cu}\) surfaces. (a) Write equations representing the reactions occurring at the metals. (b) What visual evidence would you seek to show that \(\mathrm{Cu}\) is not oxidized to \(\mathrm{Cu}^{2+} ?\) (c) At some stage, NaOH solution is added to the beaker to neutralize the HCl acid. Upon further addition of \(\mathrm{NaOH}\), a white precipitate forms. What is it?

Short Answer

Expert verified
The reactions at the metal surfaces are \( \mathrm{Mg} (s) + 2 \mathrm{HCl} (aq) \rightarrow \mathrm{MgCl}_2 (aq) + \mathrm{H}_2 (g) \) and \( \mathrm{Cu} (s) + 2 \mathrm{HCl} (aq) \rightarrow \mathrm{CuCl}_2 (aq) + \mathrm{H}_2 (g)\), though the latter does not actually occur. The absence of a blue-green color in the solution would serve as visual evidence that the copper has not been oxidized to \( \mathrm{Cu}^{2+} \). The white precipitate that forms upon the addition of NaOH is magnesium hydroxide, \( Mg(OH)_2 \).

Step by step solution

01

Construct Chemical Reaction Equations

The reactions at the two metals, magnesium and copper, can be represented as follows: At the magnesium surface: \( \mathrm{Mg} (s) + 2 \mathrm{HCl} (aq) \rightarrow \mathrm{MgCl}_2 (aq) + \mathrm{H}_2 (g) \) . This equation represents the reaction of magnesium metal with hydrochloric acid to form magnesium chloride and hydrogen gas. At the copper surface: \( \mathrm{Cu} (s) + 2 \mathrm{HCl} (aq) \rightarrow \mathrm{CuCl}_2 (aq) + \mathrm{H}_2 (g) \) . This represents the reaction of copper metal with hydrochloric acid to form copper (II) chloride and hydrogen gas. However, in this scenario, this reaction does not actually happen, as copper doesn't normally react with hydrochloric acid to form Cu2+ ions.
02

Visual Evidence for Absence of Copper Oxidation

A visual evidence would be the absence of a blue-green color in the solution. If copper is oxidized to \( \mathrm{Cu}^{2+} \), it would react with chloride ions available in the solution to form \( \mathrm{CuCl}_2 \), which gives a blue-green color. If the solution remains colorless, it indicates that the copper has not been oxidized to \( \mathrm{Cu}^{2+} \).
03

Identify the White Precipitate

Upon further addition of NaOH, a white precipitate forms which is magnesium hydroxide, \( Mg(OH)_2 \). Remember, the NaOH neutralizes the HCl acid first, and after that it reacts with the Mg2+ ions which are present in the solution (from the MgCl2 which was the product of the initial reaction between magnesium and HCl). This reaction can be formulated as follows: Mg2+ (aq) + 2OH- (aq) -> \(Mg(OH)_2 (s)\)

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Comment on whether \(\mathrm{F}_{2}\) will become a stronger oxidizing agent with increasing \(\mathrm{H}^{+}\) concentration.

The half-reaction at an electrode is $$\mathrm{Mg}^{2+}(\text { molten })+2 e^{-} \longrightarrow \mathrm{Mg}(s)$$ Calculate the number of grams of magnesium that can be produced by supplying \(1.00 \mathrm{~F}\) to the electrode.

Calculate the standard potential of the cell consisting of the \(\mathrm{Zn} / \mathrm{Zn}^{2+}\) half-cell and the \(\mathrm{SHE}\). What will the emf of the cell be if \(\left[\mathrm{Zn}^{2+}\right]=0.45 \mathrm{M}, \mathrm{P}_{\mathrm{H}_{2}}=\) \(2.0 \mathrm{~atm},\) and \(\left[\mathrm{H}^{+}\right]=1.8 \mathrm{M} ?\)

Show a sketch of a galvanic concentration cell. Each compartment consists of a Co electrode in a \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}\) solution. The concentrations in the compartments are \(2.0 \mathrm{M}\) and \(0.10 \mathrm{M}\), respectively. Label the anode and cathode compartments. Show the direction of electron flow. (a) Calculate the \(E_{\text {cell }}\) at \(25^{\circ} \mathrm{C}\). (b) What are the concentrations in the compartments when the \(E_{\text {cell }}\) drops to 0.020 V? Assume volumes to remain constant at \(1.00 \mathrm{~L}\) in each compartment.

The \(E^{\circ}\) value of one cell reaction is positive and that of another cell reaction is negative. Which cell reaction will proceed toward the formation of more products at equilibrium?
See all solutions

Recommended explanations on Chemistry Textbooks

Inorganic Chemistry

Read Explanation

Physical Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Chemical Analysis

Read Explanation

Making Measurements

Read Explanation

Organic Chemistry

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free