Percent yield and percent recovery are terms used in chemistry to describe the efficiency of a chemical reaction or a separation process. While they are related concepts, they have different meanings and implications.
What is Percentage Yield?
Percent yield is the percent ratio of actual yield to the theoretical yield. It is calculated to be the experimental yield divided by theoretical yield multiplied by 100%. If the actual and theoretical yield are the same, the percent yield is 100%. Usually, percent yield is lower than 100% because the actual yield is often less than the theoretical value. Reasons for this can include incomplete or competing reactions and loss of sample during recovery.
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. It can also be a source of error if the excess is due to incomplete removal of water or other impurities from the sample. Percent yield is always a positive value.
The equation for percent yield is:
percent yield = (actual yield/theoretical yield) x 100%
Where:
- actual yield is the amount of product obtained from a chemical reaction
- theoretical yield is the amount of product obtained from the stoichiometric or balanced equation, using the limiting reactant to determine product
Units for both actual and theoretical yield need to be the same (moles or grams).
What is Percentage Recovery?
Percent recovery computes the percentage of an original substance that is recovered after a chemical reaction is completed. These mainly include purification reactions. It also determines their efficiency. Percent recovery calculation is mainly applicable to those reactions in which the identity of the substance to be purified remains the same before and after the reaction.
In organic chemistry, some elements are purified by performing the process of recrystallization. In this process, a certain element/compound to be purified is mixed with a hot solvent. Later, the solution is cooled, such that the element/compound is precipitated. However, note that some amount of the original substance may be lost in this process. This leads to the reduction in the element’s actual quantity.
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. However, it may slightly vary from the exact value. The reason for this is, some of the original substance may be spilled out or retained in the container that has been used for recrystallization. Thus, the actual amount of the crystallized substance changes.
The equation for percent recovery is:
Percent recovery = (amount of substance recovered on purification ÷ amount of substance originally taken) × 100
The values of the initial amount and the final recovered amount of the product are required to calculate ‘percent recovery’.
Key Difference
Definition
- Percent yield is a measure of how much product is actually obtained from a chemical reaction compared to the theoretically predicted amount based on stoichiometry.
- Percent recovery refers to the proportion of a desired substance that is successfully collected after a separation process, typically after purification or extraction.
Context
- Percent yield is typically used in the context of chemical reactions, especially in the laboratory, to assess the effectiveness of a reaction in converting reactants into products.
- Percent recovery is used in the context of separation and purification processes, such as distillation, extraction, or crystallization, to determine how efficiently a target compound has been isolated from a mixture.
Calculation
- Percent yield is calculated using the formula: (Actual Yield / Theoretical Yield) × 100. The actual yield is the amount of product obtained experimentally, and the theoretical yield is the maximum amount of product that could be obtained based on stoichiometry.
- Percent recovery is calculated using the formula: (Recovered Amount / Initial Amount) × 100. The recovered amount is the actual amount of the desired compound obtained after the separation process, and the initial amount is the amount of the compound present before the process.
Implications
- A high percent yield indicates a successful reaction that efficiently converts reactants into products.
- A high percent recovery indicates that a significant amount of the target compound was successfully isolated and collected after a separation process.
Factors Affecting Values
- Factors that can lead to lower percent yield include side reactions, incomplete reactions, and losses during purification and handling.
- Factors that can lead to lower percent recovery include losses during the separation process, incomplete extraction, and losses due to handling and transfer.
Interpretation
- A lower percent yield suggests inefficiencies in the reaction, such as incomplete conversions or unwanted side reactions.
- A lower percent recovery indicates inefficiencies in the separation process, potentially resulting in loss of the desired compound.
Percentage Yield vs Percent Recovery: Key Takeaways
| Points of Comparison | Percentage Yield | Percentage Recovery |
| Description | Percent yield is the ratio between percentages of actual yield and the theoretical yield of the final product obtained from chemical synthesis. | Percent recovery is the amount of a product obtained after its synthesis and purification. |
| Use | Percent yield can be used to determine the efficiency of chemical synthesis. | Percent recovery is used to determine the amount of pure compound present in the final product of chemical synthesis. |
| Calculation | Percent yield is calculated as a ratio between actual yield and theoretical yield. Percent Yield = (Actual yield/ Theoretical yield) x 100% | Percent recovery is calculated as the ratio between the pure compound and initial compound. Percent Recovery = (Amount of purified compound / amount of original compound) x 100% |