The tarnish that forms on objects made of silver is solid silver sulfide; it can be removed by reacting it with aluminum metal to produce silver metal and solid aluminum sulfide. How many moles of the excess reactant remain unreacted when the reaction is over if 5 moles of silver sulfide react with 8 moles of aluminum metal? Hint: Write a balanced chemical equation first. Enter to 1 decimal place.

4.7 moles

Explanation:

Equation of reaction:

3Ag2S + 2Al = 6Ag + Al2S3

From the equation of reaction above,

3 moles of silver sulfide reacted with 2 moles of aluminum metal

Therefore, 5 moles of silver sulfide is required to react with (5*2/3 = 3.3 moles) of aluminum metal

The excess reactant is aluminum metal

Number of moles of aluminum metal that remain unreacted = 8 moles - 3.3 moles = 4.7 moles (to 1 decimal place)