To remove the tarnish \(\left(\mathrm{Ag}_{2} \mathrm{~S}\right)\) on a silver spoon, a student carried out the following steps. First, she placed the spoon in a large pan filled with water so the spoon was totally immersed. Next, she added a few tablespoonfuls of baking soda (sodium bicarbonate), which readily dissolved. Finally, she placed some aluminum foil at the bottom of the pan in contact with the spoon and then heated the solution to about \(80^{\circ} \mathrm{C}\). After a few minutes, the spoon was removed and rinsed with cold water. The tarnish was gone and the spoon regained its original shiny appearance. (a) Describe with equations the electrochemical basis for the procedure. (b) Adding \(\mathrm{NaCl}\) instead of \(\mathrm{NaHCO}_{3}\) would also work because both compounds are strong electrolytes. What is the added advantage of using \(\mathrm{NaHCO}_{3}\) ? (Hint: Consider the \(\mathrm{pH}\) of the solution.) (c) What is the purpose of heating the solution? (d) Some commercial tarnish removers containing a fluid (or paste) that is a dilute \(\mathrm{HCl}\) solution. Rubbing the spoon with the fluid will also remove the tarnish. Name two disadvantages of using this procedure compared to the one described here.

Step by step solution

01

Describe Electrochemical Basis with Equations

Aluminum has a greater Activity Series than silver, meaning it gives up electrons more readily than silver. When aluminum comes in contact with tarnish (\(\mathrm{Ag}_2 \mathrm{S}\)), it will steal sulfur atom and hence free the silver atom. This can be represented by the following equations: \[3\mathrm{Ag}_2 \mathrm{S}(s)+2\mathrm{Al}(s) \rightarrow 6\mathrm{Ag}(s)+\mathrm{Al}_2 \mathrm{S}_3(s)\] The tarnish on the silver spoon is basically silver sulfide (\(\mathrm{Ag}_2 \mathrm{S}\)) and aluminum can react with silver sulfide to form aluminum sulfide, freeing the silver atoms in the process.

02

Advantage of Using \(\mathrm{NaHCO}_{3}\)

Both \(\mathrm{NaCl}\) and \(\mathrm{NaHCO}_{3}\) can work because they are strong electrolytes, meaning they can generate free ions in the solution that can facilitate the electron transfer between aluminum and silver. The advantage of using \(\mathrm{NaHCO}_{3}\) (baking soda) is that it is a weaker base than \(\mathrm{NaCl}\) Sodium Chloride, making the solution less basic. This lower pH will provide an environment that is less harsh for the silverware.

03

Purpose of Heating the Solution

The purpose of heating the solution is to increase the rate of the chemical reaction occurring. Increasing the temperature enhances the kinetic energy of the particles, causing them to move faster and collide more frequently and with greater energy, leading to a faster reaction.

04

Disadvantages of Using Dilute \(\mathrm{HCl}\) Solution

Commercial tarnish removers containing dilute \(\mathrm{HCl}\) solution have a couple of disadvantages. First, \(\mathrm{HCl}\) is a strong acid and potentially harmful, it can corrode the silver if left on for too long or if used too frequently. Secondly, it requires physical scrubbing or rubbing which can scratch the silver if one isn't careful or using the wrong type of cleaning cloth.

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