12 past paper MCQs on Yield, from the Fundamental Concepts of Chemistry unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.
1.30 grams of ethanol are mixed with excess acidified $\mathrm{K_2Cr_2O_7}$ and boiled under reflux. The organic product is collected by distillation and the yield is 75.0%. What is the mass of product produced? (MDCAT 2022)
Correct answer: (d) 29 g
$30/46=0.65$ mol of ethanol would give $0.65\times60=39$ g of ethanoic acid, and 75% of that is about 29 g.
2.Consider the given balanced chemical equation: 2H2 + O2 -> 2H2O If 4 g of H2 reacts with 32 g of O2 to produce 28 g of H2O, what is the percentage yield of the reaction? (Molar mass of H2 = 2 g/mol, O2 = 32 g/mol and H2O = 18 g/mol) (UHS MDCAT 2025)
Correct answer: (b) 77.8%
Four grams of hydrogen would give $36\,\mathrm{g}$ of water, so the yield is $28/36$, or $77.8\%$.
3.A chemical reaction has a theoretical yield of 25 g, but only 20 g of product was obtained. What is the percentage yield of the reaction? (UHS MDCAT 2025)
Correct answer: (d) 80%
The yield is the actual over the theoretical, $20/25$, which is $80\%$.
4.If % yield and actual yield is 80 and 20g respectively, what will be theoretical yield? (UHS MDCAT 2025)
Correct answer: (b) 25g
The theoretical yield is the actual divided by the fraction, $20/0.8$, which is $25\,\mathrm{g}$.
5.Heating 24.8g of copper carbonate (CuCO3) in a crucible produced only 13.9g of copper oxide (CuO). What is the percentage yield of copper oxide? (KMU MDCAT 2024)
Correct answer: (c) 86.87%
$24.8\,\mathrm{g}$ is $0.2$ mole, which should give $16\,\mathrm{g}$ of the oxide, and $13.9/16$ is $86.87\%$.
6.Efficiency of chemical reaction can be checked by calculating (KMU MDCAT 2024)
Correct answer: (c) Percentage yield
The percentage yield compares what was got with what was possible, so it measures the efficiency.
7.Actual yield will reach the ideal (theoretical) value if the % yield of the reaction is, (KMU MDCAT 2024)
Correct answer: (d) 100%
A hundred per cent yield is exactly the case where the actual yield equals the theoretical one.
8.30 grams of 2-propanol were mixed with excess acidified K2Cr2O7 and boiled under reflux for 20 minutes. The organic product was then collected by distillation. The yield of product was 75.0%. What is the mass of product produced? (UHS MDCAT 2023)
Correct answer: (b) 21.75g
Half a mole of the alcohol would give half a mole, $29\,\mathrm{g}$, of acetone, and three quarters of that is $21.75\,\mathrm{g}$.
9.The amount of product according to the balanced chemical equation is called as? (PMC MDCAT 2022)
Correct answer: (a) Theoretical yield
The amount the equation says is possible is the theoretical yield.
10.In a particular chemical reaction the actual yield was 70gm, while that of Its theoretical yield Is 100gm. The pecentage yield of the said reatlon is: (PMC MDCAT 2022)
Correct answer: (b) 70%
$70/100$ is a yield of $70\%$.
11.Actual yield is always less than theoretical yield due to? (PMC Practice 2021)
Correct answer: (d) All of these options are correct
Some product is lost in handling, some reactions reverse and some go another way.
12.The efficiency of chemical reaction can be expressed as: (PMC MDCAT 2020)
Correct answer: (c) % yield
The percentage yield compares what was got with what was possible.