Determine the limiting reagent and the theoretical yield of urea [(NH2) 2CO]

Question

Suppose that 4.75 g of NH3 are mixed with 7.50 g of CO2. Determine the limiting reagent and the theoretical yield of urea [(NH2) 2CO].

b) How many grams are needed to prepare 25.00 mL of a 5% m / v solution of sodium bicarbonate? 

Answer 1

a) You need the balanced reaction in order to do a LR problem which you can't know unless you know the ammonium carbamate reaction to urea. (Can't balance without the water in products)

2NH₃ + CO₂ --> (NH₂)₂CO + H₂O

Finding the theoretical yield in an LR problem, it's probably easiest to start with each reactant and calculate the product. The one that gives you the least product is the LR and the amount of product is the answer to (a). I will do NH₃ and leave CO₂ for your (usual 3-step stoichiometry)

4.75 g Amm x (1 mole/ 17 g Amm) *(1mole Urea/2 moles Amm)*(60.06 g Urea/mole) = g of urea

b) The ridiculous unit of 5 % mass/volume (% is meaningful only when the units are the same) really mean 5 grams of baking soda / 100 ml of solution. (It is really a mass concentration akin to a molarity)

25 ml soln *(5 g BS/100 ml soln) = g of BS

Please consider a tutor.