The tarnish that forms on objects made of silver is solid silver sulphide. this can be removed by reacting it with aluminium metal to produce silver metal and solid aluminium sulphide. how many moles of the excess reactant remain unreacted after the reaction between 3.4 moles of silver sulphide with 8.1 moles of aluminium metal is finished?

5.83 mol.

Explanation:

From the balanced reaction:

2Al + 3Ag₂S → 6Ag + Al₂S₃,

It is clear that 2 mol of Al react with 3 mol of Ag₂S to produce 1 mol of Ag and 1 mol of Al₂S₃.

Al reacts with Ag₂S with (2: 3) molar ratio.

So, 2.27 mol of Al reacts completely with 3.4 mol of Ag₂S with (2: 3) molar ratio.

The limiting reactant is Ag₂S.The excess "left over" reactant is Al.

The reamining moles of excess reactant "Al" = 8.1 mol - 2.27 mol = 5.83 mol.

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