Chapter 19, Problem 114AP

To remove the tarnish $\left({\text{Ag}}_{\text{2}}\text{S}\right)$ 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 $\text{80°C}$. 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 ${\text{NaCl instead of NaHCO}}_{\text{3}}$ would also work because both compounds are strong electrolytes. What is the added advantage of using ${\text{NaHCO}}_{\text{3}}$ ? (Hint: Consider the pH of the solution.) (c) What is the purpose of heating the solution? (d) Some commercial tarnish removers contain a fluid (or paste) that is a dilute 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 previously.