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. This ScienceStruck article explains how to calculate the percent recovery of any purified substance.
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.
When we use a certain substance for a reaction, it changes during the course of the reaction. Percent recovery refers to the amount of the original substance retained after the completion of the reaction. In a recrystallization reaction, the original substance is recrystallized, after which, its recovery value can be computed.
The values of the initial amount and the final recovered amount of the product are required to calculate ‘percent recovery’.
- Weigh the original amount of the substance. Record the value.
- Complete the purification process.
- On purifying the desired material, leave it aside to dry. This can be done by simply placing it at room temperature or mildly heating it.
- Remember to remove any other material, such as a filter paper, used in the process.
- Weigh the dried substance and record the value.
- Compute the value of percent recovery using the formula explained below.
The equation for percent recovery is quite simple. All we need to know is the original and final amount of the substance under consideration.
It can also be expressed in terms of the purity of substance.
11.23 gm of zinc is used as a reactant in a recrystallization reaction. At the end of the reaction, 8.67 gm of zinc is retained in the flask. Calculate the percentage recovery of zinc.
Data given:
Amount of zinc (original) = 11.23 gm
Amount of zinc recovered = 8.67 gm
Solution:
Percent recovery = (amount of substance recovered on purification ÷ amount of substance originally taken) × 100
Percent recovery = (8.67 ÷ 11.23) × 100 = 77.20 %
77.20% of zinc is recouped in this process.
Problem II:
14.18 gm of copper is used for a recrystallization experiment. The amount of copper recovered at the end of the purification process is 18.29 gm. Calculate the percentage of copper recovered in the process.
Data given:
Amount of copper (original) = 14.18 gm
Amount of copper recovered = 18.29 gm
Solution:
Calculating using the same formula used in problem I.
Percent recovery = (18.29 ÷ 14.18) × 100 = 128.98 %
This value is above 100%, which indicates that some error has occurred. This could be because the copper has some water content, as it was not dried properly before weighing.
For Any Substance (in grams)
From the above calculations, we can conclude that the percent recovery calculation helps us estimate the original amount of a certain substance that needs to be taken in order to get to the final quantity.
