Show the calculation of (1) the expected grams of urea (CH4N2O) formed in the reaction of 6.5 grams of lead cyanate (Pb(CNO)2) with excess ammonium hydroxide and then show the calculation of (2) the % yield if the actual yield of urea is 1.89 grams. Reaction is shown below:
Pb(CNO)2 + 2 NH4OH → Pb(OH)2 + 2 (H2N)2CO (Urea)
To calculate the expected grams of urea formed in the reaction of 6.5 grams of lead cyanate (Pb(CNO)2), we need to use the stoichiometry of the balanced chemical equation:
Pb(CNO)2 + 2 NH4OH → Pb(OH)2 + 2 (H2N)2CO
Step 1: Convert the mass of Pb(CNO)2 to moles.
To do this, we need to know the molar mass of Pb(CNO)2.
Pb(CNO)2:
Pb: Atomic mass of Pb = 207.2 g/mol
C: Atomic mass of C = 12.01 g/mol
N: Atomic mass of N = 14.01 g/mol
O: Atomic mass of O = 16.00 g/mol
Molar mass of Pb(CNO)2 = (207.2 + 12.01 + 14.01 + (16.00 * 2)) g/mol
= 207.2 + 12.01 + 14.01 + 32.00
= 265.22 g/mol
Now, we can calculate the number of moles of Pb(CNO)2:
Number of moles of Pb(CNO)2 = mass of Pb(CNO)2 / molar mass of Pb(CNO)2
= 6.5 g / 265.22 g/mol
Step 2: Use the stoichiometry to convert moles of Pb(CNO)2 to moles of urea (H2N)2CO.
From the balanced chemical equation, we see that the stoichiometry between Pb(CNO)2 and (H2N)2CO is 1:2.
Number of moles of (H2N)2CO = Number of moles of Pb(CNO)2 * (2 moles of (H2N)2CO / 1 mole of Pb(CNO)2)
Step 3: Convert moles of urea (H2N)2CO to mass.
To do this, we need to know the molar mass of (H2N)2CO.
(H2N)2CO:
H: Atomic mass of H = 1.01 g/mol
N: Atomic mass of N = 14.01 g/mol
C: Atomic mass of C = 12.01 g/mol
O: Atomic mass of O = 16.00 g/mol
Molar mass of (H2N)2CO = (2 * 1.01) + (14.01 * 2) + 12.01 + 16.00
= 2.02 + 28.02 + 12.01 + 16.00
= 58.05 g/mol
Mass of (H2N)2CO = Number of moles of (H2N)2CO * molar mass of (H2N)2CO
This calculation gives us the expected grams of urea formed in the reaction.
Now, to calculate the percent yield, we compare the actual yield to the expected yield.
Percent Yield = (Actual Yield / Expected Yield) x 100
Given that the actual yield of urea is 1.89 grams and the expected yield is the value obtained from the previous calculation, you can substitute these values into the percent yield formula to find the answer.