In this simple chemistry activity, kids help you polish the silver! Simple explanation: Ever noticed how some pieces of silver have a dark coating? This is tarnish. Silver, like many other metals, changes color over time due to a chemical reaction with the air. You can reverse this tarnish with a different chemical reaction.
The details: Silver reacts with compounds in the air that contain sulfur. This creates a thin, dull, brown or black covering of silver sulfide over the metal. Silver can be cleaned either by rubbing away the tarnish or by reversing the chemical reaction that caused the tarnish. In this activity, we reverse the tarnish, releasing the sulfides (this is what smells like rotten eggs) and turning the silver sulfide back into plain old shiny silver. Many metals will form compounds with sulfur – and some, like aluminum, actually have a greater affinity for sulfur than silver. So when silver and aluminum are soaked together in a baking soda and salt solution, the sulfur transfers from the silver to the aluminum!
The bubbling and fizzing you see in this activity is actually the vinegar (an acid) reacting with the baking soda (a base). This helps to speed the transfer of the sulfides.
- Young children should be supervised around boiling water; it can cause severe burns.
- Do not try this activity with expensive or very old silver pieces — it can remove desirable patina or tarnish.
- Glass baking dish
- 1 sheet of aluminum foil
- 1 Tablespoon salt
- 1 Tablespoon baking soda
- 1 cup boiling water
- 1/2 cup white vinegar
- tarnished silver
- soft cloth for drying and polishing
Place a sheet of aluminum foil in the bottom of the glass baking dish. (Don't use a metal pan unless you are sure it is aluminum, as this will change the chemical reaction.)
Add 1 Tablespoon of salt and 1 Tablespoon of baking soda to the baking dish.
In a separate cup, combine 1 cup boiling water with 1/2 cup vinegar.
Pour the hot liquids into the baking dish. Note the instant chemical reaction. This is the vinegar (an acid) reacting with the baking soda (a base).
Now add tarnished silver. In some cases, the tarnish will disappear instantly. In other cases, the item will need to soak for up to 30 minutes.
Note the slight smell of rotton eggs; this is evidence of the chemical reaction where the sulfides are moving from the silver to the aluminum.
Remove the silver from the solution and wipe dry with a soft cloth. You may need to rub out tough spots, or soak longer.