Question

The human body excretes nitrogen in the form of urea, NH₂CONH₂. The key biochemical step in urea formation is the reaction of water with arginine to produce urea and ornithine:

(a) What is the mass percent of nitrogen in urea, arginine, and ornithine? (b) How many grams of nitrogen can be excreted as urea when 135.2 g of ornithine is produced?

Short answer

1. The mass percentage of nitrogen in urea as: 46.65% N in urea, 32.16% N in arginine and 21.2 % in ornithine.

There are 28.66 g Ncan be excreted as urea when 135.2 g or ornithine is produced.

Step-by-step solution

Calculating the mass percent of nitrogen in urea, arginine and ornithine

The mass percentage can be calculated as,

$$\begin{gathered} Mass\%ofN=\frac{molesofNinformula\times molarmassofN}{massof1molofcompound}\times 100 \\ Mass\%ofN=\frac{2molN\times {\displaystyle \frac{14.01gN}{1molN}}}{60.07gC{H}_4{N}_{2}O}\times 100=46.65\%Ninurea \\ Mass\%ofN=\frac{2molN\times {\displaystyle \frac{14.01gN}{1molN}}}{132.19g{C}_5{H}_{12}{N}_2{O}_2}\times 100=21.2\%Ninornithine \end{gathered}$$

Calculating the mass percent of N

On calculating the mass of urea,

$$\begin{gathered} Massofurea=135.2g{C}_5{H}_{12}{N}_2{O}_2\times \frac{1mol{C}_5{H}_{12}{N}_2{O}_2}{132.19g{C}_5{H}_{12}{N}_2{O}_2}\times \frac{1molC{H}_4{N}_{2}O}{1mol{C}_5{H}_{12}{N}_2{O}_2}\times \frac{60.07gC{H}_4{N}_{2}O}{1molC{H}_4{N}_{2}O} \\ Massofurea=0.4665\times 61.4378gC{H}_4{N}_{2}O \\ MassofN=0.4665\times 61.4378gC{H}_4{N}_{2}O=28.66gN \end{gathered}$$