What's the limiting reagent?

Question

Initially there is a .500g sample of CuSO4.5H2O and a .245g sample of NH2CH2CO2H (glycine).

We find that there are .002002 moles CuSO4.5H2O and .003264 moles NH2CH2CO2H (glycine). What is the limiting reagent?

How many grams Cu(gly)2.H2O are expected based on the limiting reagent?

Answer 1

The limiting reagent is the one that runs out first and thus limits the amount of product that can be created from a specified amount of reactants.

You need the check the BALANCED equation carefully because reactants do not always react in a 1 to 1 ratio, so the reactant with the greater number of moles may actually run out first in some cases!

In your example: Cu(gly)2 .H2O, apparantly 2 glycines react with one copper. You would need 2 x 0.002002 or 0.004004 moles of glycine to react with all the copper, but you only have 0.003264moles, so some copper will be left over. To get the expected grams of Cu(gly)2.H2O you need the moles of LIMITING reagant and the reaction ratio from a BALANCED equation.

Molar mass of Cu(gly)2.H2O =

63.55 + [(2 x 12.01) + (5 x 1.01) + (2 x 16.00) + 14.01] x 2 +

(2 x 1.01) + 16.00 = 63.55 + [75.08] x 2 + 18 = 231.7g/mole

For you case: 0.003264 mole x (1/2) x 231.7g/mole = 0.378g