Question

A voltaic cell similar to that shown in Figure 20.5 is constructed. One electrode half-cell consists of a silver strip placed in a solution of \(\mathrm{AgNO}_{3}\), and the other has an iron strip placed in a solution of \(\mathrm{FeCl}_{2}\). The overall cell reaction is $$\mathrm{Fe}(s)+2 \mathrm{Ag}^{+}(a q) \longrightarrow \mathrm{Fe}^{2+}(a q)+2 \mathrm{Ag}(s)$$ (a) What is being oxidized, and what is being reduced? (b) Write the half-reactions that occur in the two half-cells. (c) Which electrode is the anode, and which is the cathode? (d) Indicate the signs of the electrodes. (e) Do electrons flow from the silver electrode to the iron electrode or from the iron to the silver? (f) In which directions do the cations and anions migrate through the solution?

Short answer

In the given voltaic cell, iron (Fe) is being oxidized and silver ions (Ag+) are being reduced. The half-reactions are: \( \mathrm{Fe}(s) \longrightarrow \mathrm{Fe}^{2+}(a q) + 2e^{-} \) (oxidation) and \( 2 \mathrm{Ag}^{+}(a q) + 2e^{-} \longrightarrow 2 \mathrm{Ag}(s) \) (reduction). The iron electrode is the anode (negative) and the silver electrode is the cathode (positive). Electrons flow from the iron electrode to the silver electrode. Ag+ ions move towards the silver electrode (cathode) and Cl- ions move towards the iron electrode (anode).

Step-by-step solution

Identifying Oxidation and Reduction Processes

In the overall cell reaction, we can identify the species being oxidized and reduced. Oxidation is the process of losing electrons, while reduction is the process of gaining electrons. The overall cell reaction is given as: \[\mathrm{Fe}(s)+2 \mathrm{Ag}^{+}(a q) \longrightarrow \mathrm{Fe}^{2+}(a q)+2 \mathrm{Ag}(s)\] From the given reaction, we can see that Fe is losing 2 electrons (going from neutral Fe to Fe^(2+)), thus it is being oxidized. On the other hand, Ag^(+) is gaining electrons (going from Ag^(+) to neutral Ag), thus it is being reduced.

Writing Half-Reactions

We can now write the half-reactions for the two half-cells. The oxidation half-reaction is: \[\mathrm{Fe}(s) \longrightarrow \mathrm{Fe}^{2+}(a q) + 2e^{-}\] The reduction half-reaction is: \(2 \mathrm{Ag}^{+}(a q) + 2e^{-} \longrightarrow 2 \mathrm{Ag}(s)\)

Identifying Anode and Cathode

In a voltaic cell, oxidation occurs at the anode, and reduction occurs at the cathode. From our half-reactions, we know that the iron strip is undergoing oxidation; thus, it is the anode. The silver strip is undergoing reduction, so it is the cathode.

Indicating the Signs of the Electrodes

By convention, the anode has a negative sign, and the cathode has a positive sign. Therefore, the iron electrode (the anode) is negative, and the silver electrode (the cathode) is positive.

Determining the Direction of Electron Flow

Electrons flow from the anode to the cathode in a voltaic cell. In this case, electrons flow from the iron electrode (anode) to the silver electrode (cathode).

Direction of Cations and Anions Migration

In the electrolyte solution, cations (positively charged ions) migrate towards the cathode (negatively charged), and anions (negatively charged ions) migrate towards the anode (positively charged). Therefore, Ag+ ions will move towards the silver electrode (cathode), and Cl- ions will move towards the iron electrode (anode).

Key concepts

Oxidation and Reduction

In the fascinating world of chemistry, oxidation and reduction are like two sides of a coin - a reaction can't have one without the other! In a nutshell, oxidation is the process where an atom loses electrons, and reduction is when an atom gains them. Think of it as a kind of chemical tug-of-war with electrons as the prize.

Oxidation isn't just about losing electrons – it's also associated with an increase in oxidation state. Conversely, reduction brings not only a gain in electrons but also a decrease in oxidation state.

Electrochemical Cells

Diving into the realm of electrochemical cells, we find devices that convert chemical energy into electrical energy through spontaneous redox reactions. The cell described in the exercise is a voltaic cell, one of the two main types of electrochemical cells, the other being the electrolytic cell.

A voltaic cell has two half-cells where reactions take place. These are connected by a salt bridge or a porous membrane, allowing ions to move freely but keeping the solutions separate. This setup is how we harness chemical reactions to produce power! Isn't it electrifying?

Anode and Cathode Identification

When you're trying to figure out which electrode is the anode and which is the cathode, here's the deal: the anode is where oxidation happens - electrons are given up by the metal. This electrode will have a negative charge in a voltaic cell. On the other side, you've got the cathode, which is all about reduction - snagging those electrons! This one's positively charged in a voltaic cell.

So remember, an 'A' for anode, 'O' for oxidation, and both are negative, like the first letter in 'anxious.' For the cathode, it's 'C' for cathode, 'R' for reduction, and positively charged, rather like the first letter in 'cheerful'.

Electron Flow Direction

Here's a tip to remember about electron flow direction: electrons always take a hike from the anode to the cathode in electrochemical cells. So, in our voltaic cell exercise, the iron electrode is handing over those electrons like they're going out of style, and the silver electrode is on the receiving end. It's like an electronic conveyor belt moving the electrons from iron (anode) to silver (cathode).

Ion Migration in Electrolyte

Now, let’s talk ions and their migration patterns in the electrolyte. It's like rush hour in the electrolyte where everyone's on the move. Cations, the positively charged ions, are attracted to the cathode, just like how opposite polls of magnets attract. Analogously, anions, which have a negative charge, are pulled towards the anode.

So, if you ever find yourself in a salt solution during a chemistry experiment, remember this: cations (+) go to the cathode (-), and anions (-) go to the anode (+). It's a charged dance of attraction within the electrolyte.