Answer : The amount of reactant left in excess is 13.1075 grams.
Explanation : Given,
Mass of
= 26.5 g
Mass of
= 10 g
Molar mass of
= 53.5 g/mole
Molar mass of
= 40 g/mole
First we have to calculate the moles of
and
.


Now we have to calculate the limiting and excess reagent.
The balanced chemical reaction is,

From the balanced reaction we conclude that
As, 1 mole of
react with 1 mole of

So, 0.25 moles of
react with 0.25 moles of

From this we conclude that,
is an excess reagent because the given moles are greater than the required moles and
is a limiting reagent and it limits the formation of product.
Moles of remaining excess reactant = 0.495 - 0.25 = 0.245 moles
Now we have to calculate the mass of
.


Therefore, the amount of reactant left in excess is 13.1075 grams.