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# Calculating the Percent Yield of Alum

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❶Convert the mass of ZnS to moles:

## Calculating Percent Yield Example   Managers evaluate the productivity of a process by measuring the number of finished products, known as outputs , against the time, materials and energy -- the inputs -- needed to create them. Businesses often use time as the standard input measure. For instance, workers at Fictional Furniture can assemble 80 chairs in an eight-hour day. Since no production process can produce flawless outputs each time, some products will not be available for sale immediately after production. Some of these products can go through a different process to remove defects and become salable items.

A good unit is an output that is ready for sale right away. A reworked unit is an output that goes through the process of removing the defects and preparing it for sale. At the Fictional Furniture factory, a reworked chair may need to have its legs replaced, its back refinished or its seat reinforced to have it ready for sale. The formula for the product yield is the sum of the good units and the reworked units available for sale.

The formula looks like this:. Look at the balanced equation for the reaction. The coefficients in front of each molecule tell you the ratio of the molecules that you need for the reaction to occur.

If you use exactly the ratio given by the formula, then both reactants should be used equally. The coefficients indicate that you need 6 oxygen molecules for every 1 glucose molecule. Compare the ratios to find the limiting reactant. In most chemical reactions, one of the reactants will be used up before the others. The one that gets used up first is called the limiting reactant. This limiting reactant determines how long the chemical reaction can take place and the theoretical yield you can expect.

Compare the two ratios you calculated to identify the limiting reactant: The formula tells you that your ideal ratio is 6 times as much oxygen as glucose. Therefore, you have more oxygen than required. Thus, the other reactant, glucose in this case, is the limiting reactant. Review the reaction to find the desired product. The right side of a chemical equation shows the products created by the reaction. The coefficients of each product, if the reaction is balanced, tells you the amount to expect, in molecular ratios.

Each product has a theoretical yield, meaning the amount of product you would expect to get if the reaction is perfectly efficient. The two products shown on the right are carbon dioxide and water. You can begin with either product to calculate theoretical yield. In some cases, you may be concerned only with one product or the other. If so, that is the one you would start with. Write down the number of moles of your limiting reactant.

You must always compare moles of reactant to moles of product. If you try to compare the mass of each, you will not reach the correct results. The molar mass calculations found that the initial 25g of glucose are equal to 0.

Compare the ratio of molecules in product and reactant. Return to the balanced equation. Divide the number of molecules of your desired product by the number of molecules of your limiting reactant. In other words, this reaction can produce 6 molecules of carbon dioxide from one molecule of glucose. Multiply the ratio by the limiting reactant's quantity in moles.

The answer is the theoretical yield, in moles, of the desired product. In this example, the 25g of glucose equate to 0. The ratio of carbon dioxide to glucose is 6: You expect to create six times as many moles of carbon dioxide as you have of glucose to begin with. The theoretical yield of carbon dioxide is 0. You should get 8. Determine the percent yield.

Your result should be The calculation from the mass of Al to the mass of alum could be done in a single step Help Me. The stoichiometric factor is the ratio of the stoichiometric coefficients of two substances in a balanced chemical equation. The stoichiometric coefficients are the numbers in front of the substances and represent the number of moles of each that are required for, or are formed in, the reaction. In this case, 2 moles of Al are required contents and 2 moles of alum are formed. ## Main Topics

In calculating the percent yield, we need to calculate the theoretical yield based on the limiting reactant. If there is more than one reactant, this is the reactant that produces a smaller amount.

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Limiting reagents and percent yield How to determine the limiting reagent, and using stoichiometry to calculate the theoretical and percent yield. Google Classroom Facebook Twitter.