Worksheet 5-3: Basic percent yield problems
1. Assume the following hypothetical reaction takes place:
2 A + 7 B à 4 C + 3 D
Calculate the percent yield in each of the following cases:
a. The reaction of 0.0251 mol of A produces 0.0349 mol of C.
b. The reaction of 1.19 mol of A produces 1.41 mol of D.
c. The reaction of 189 mol of B produces 39 mol of D.
d. The reaction of 3500 mol of B produces 1700 mol of C.
2. Elemental phosphorous can be produced be heating calcium phosphate from rocks with silica sand (SiO2) and carbon in the form of coke. The following reaction takes place.
Ca3(PO4)2 + 3 SiO2 + 5 C à 3 CaSiO3 + 2 P + 5 CO
a. If 57 mol of Ca3(PO4)2 is used and 101 mol of CaSiO3 is obtained, what is the percent yield?
b. Determine the percent yield obtained if 1280 mol of carbon is consumed and 622 mol of CaSiO3 is produced.
3. Tungsten (W) can be produced from its oxide by reacting the oxide with hydrogen at a high temperature according to the following equation:
WO3 + 3 H2 à W + 3 H2O
What is the percent yield if 56.9 g of WO3 yields 41.4 g of tungsten?
4. Carbon tetrachloride, CCl4, is a solvent that was once used in large quantities in dry cleaning. Because it is a dense liquid that does not burn, it was also used in fire extinguishers. Unfortunately, its use has been discontinued because it was found to be a carcinogen. It was manufactured by the following reaction:
CS2 + 3 Cl2 à CCl4 + S2Cl2
a. What is the percent yield of CCl4 if 719 g is produced from the reaction of 410 g of CS2.
b. If 67.5 g of Cl2 are used in the reaction and 39.5 g of S2Cl2 is produced, what is the percent yield?
5. Nitrogen dioxide, NO2, can be converted to dinitrogen pentoxide, N2O5, by reacting it with ozone, O3. The reaction of NO2 takes place according to the following equation:
2 NO2 + O3 à N2O5 + O2
Calculate the percent yield for a reaction in which 0.38 g of NO2 reacts and 0.36 g of N2O5 is recovered.
More complex percent yield problems
6. Recall the equation from question #5:
2 NO2 + O3 à N2O5 + O2
What mass of N2O5 will result from the reaction of 6.0 mol of NO2 if there is a 61.1% yield in the reaction?
7. Recall the equation from question #3:
WO3 + 3 H2 à W + 3 H2O
a. How many moles of tungsten will be produced from 3.72 g of WO3 if the yield is 92.0%?
b. A chemist carries out this reaction and obtains 11.4 g of tungsten. If the percent yield is 89.4%, what mass of WO3 was used?
8. Recall the equation from question #4:
CS2 + 3 Cl2 à CCl4 + S2Cl2
If the percent yield of the industrial process is 83.3%, how many grams of CS2 should be reacted to obtain 50000 g of CCl4?
9. Water can be separated into its elements by passing electricity through it, as shown in the following equation:
2 H2O à 2 H2 + O2
If 26 g of H2O is reacted and the process has a percent yield of 87%, what mass of O2 is produced?
10. In the past, hydrogen chloride, HCl, was made using the salt-cake method as shown in the following equation:
2 NaCl(s) + H2SO4(aq) à Na2SO4(s) + 2 HCl(g)
If 30.0 g of NaCl and 0.25 mol of H2SO4 are available, and 14.6 g of HCl is made, what is the percent yield?
Answers:
1.a. 69.5% 4. a. 86.8% 8. 29 700 g
b. 79.0% b. 92.2%
c. 48% 9. 20.08 g
d. 85% 5. 81%
10. 80.1 %
2. a. 59% 6. 200 g
b. 81%
7.a. 0.0148 mol
3. 91.8% b. 16.1