Percent yield is the percent ratio of actual yield to the theoretical yield. It’s possible for percent yield to be over 100%, which means more sample was recovered from a reaction than predicted. This can happen when other reactions were occurring that also formed the product.

Thus, to put it simply, a chemical reaction can never have 110% actual yield, or anything beyond 100% for that matter. For example, the mass of a solid product may be heavier than the solid reactants because of its reaction with gaseous substances.

The amount of acetanilide that will come out of solution is (5 – 0.53) or 4.47 g. The maximum percent recovery is then 4.47/5 = 0.89 or 89%.

Percent yield compares the hands-on results to the calculated predictions. In a perfect world, our experiments would give 100% yield, meaning that we could carry out our lab activities perfectly producing the predicted amount of product. Percent yields can be higher or lower than 100%.

There are two cases of percent recovery yield: below 100% and above 100%. The value above 100% is the inaccurate value due to erroneous calculation/weighing. The value below 100% is usually the desired value.

How to Improve Your Yield

1. Add reagents dropwise if necessary.
2. Continuously stir thoroughly.
3. Carefully keep temperature of reaction and liquid reagents at the correct level during addition and reaction.
4. Monitor your reaction carefully throughout the experiment.

Le Châtelier’s Principle states that a change in pressure, temperature, or concentration will push the equilibrium to one side of the chemical equation. So, if you manipulate the conditions to favour the product side, you increase the yield.

The actual yield is the amount of product that is actually formed when the reaction is carried out in the laboratory. However, percent yields greater than 100% are possible if the measured product of the reaction contains impurities that cause its mass to be greater than it actually would be if the product was pure.

The yield and rate of a chemical reaction depend on conditions such as temperature and pressure. In industry, chemical engineers design processes that maximise the yield and the rate at which the product is produced. They also aim to reduce waste and energy costs at all stages of the process.

Catalysts only affect the rate of reaction – they do not affect the yield of the reaction. A catalysed reaction produces the same amount of product as an uncatalysed reaction but it produces the product at a faster rate.

Catalysts increase the rate of reaction without affecting the yield.

According to the 1996 edition of Vogel’s Textbook , yields close to 100% are called quantitative, yields above 90% are called excellent, yields above 80% are very good, yields above 70% are good, yields above 50% are fair, and yields below 40% are called poor.

The higher the percentage yield is, the more efficient the reaction. Esterification and other reversible reactions can never result in 100 per cent conversion of reactants into products.

Think of percent yield as a grade for the experiment: 90 is great, 70-80 very good, 50-70 good, 40-50 acceptable, 20-40 poor, 5-20 very poor, etc.

For a synthesis – to find the overall percent yield, multiply the individual percent yields of every step by each other (ex. 3 steps, all 30% yield – 0.30 x 0.30 x 0.30 = 0.27 x 100 = 27% overall).

Calculating Percent Yield Multiply the expected moles of the product by its molar mass. For example, the molar mass of HF is 20 grams. Therefore, if you expect 4 moles of HF, the theoretical yield is 80 grams. Divide the actual yield of the product by the theoretical yield and multiply by 100.

Explanation: In some cases, the measurement may be so difficult that a 10 % error or even higher may be acceptable. In other cases, a 1 % error may be too high. Most high school and introductory university instructors will accept a 5 % error. In most cases, a percent error of less than 10% will be acceptable.

The actual yield of a reaction is the actual amount of product that is produced in the laboratory. The percentage of the theoretical yield that is actually produced (actual yield) is known as the percent yield. Percent error is always an absolute value… no negatives!

If you use too much solvent, less of the compound you’re trying to purify recrystallizes (more remains in solution), and you’ll get a low percent recovery. The purity will decrease and the percent yield will increase slightly. Slower cooling tends to give larger more pure crystals.

A percent recovery less than 100% indicate either an incomplete reaction and thereactants are not completely converted to products.

Percent recovery is the amount of a product obtained after its synthesis and purification. The percent recovery can be used to determine the efficiency of the synthesis reaction. This term is often used in organic chemistry to determine the yield obtained from recrystallization.

a. A few reasons why percent recovery is less than a 100% is because (1)the reactants are not completely converted into products. If a reverse reaction were to occur, the final state would contain both reactants and products in the chemical equilibrium.

6 Answers

• Your math is wrong. Worth double checking and easy to rule out as a source of error.
• You used more reactant than you thought.
• You actually have less product than you think.

An actual yield is the mass of a product actually obtained from the reaction. It is usually less than the theoretical yield . The reasons for this include: incomplete reactions, in which some of the reactants do not react to form the product.

Percent recovery = amount of substance you actually collected / amount of substance you were supposed to collect, as a percent. Let’s say you had 10.0g of impure material and after recrystallization you collected 7.0 g of dry pure material. Then your percent recovery is 70% (7/10 x 100).

In spike-and-recovery, a known amount of analyte is added (spiked) into the natural test sample matrix and its response is measured (recovered) in the assay by comparison to an identical spike in the standard diluent. A spike-and-recovery experiment is designed to assess this difference in assay response.

Spike sample – A sample to which known concentrations of specific analytes have been added in such a manner as to minimize the change in the matrix of the original sample. Every spiked sample analyzed should have an associated reference to the spike solution and the volume added.

The usual method involves using a low-level sample containing a known spike of analyte (or just a high-level sample without spike), and then testing several different dilutions of that sample in the chosen sample diluent.