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Introduction

Percent Yield Lab Introduction When a chemical reaction occurs and two reactants mix, we should in theory be able to determine the amount of each product formed using stoichiometric calculations. The maximum value of the final product is limited to the limiting reagent not the reagent in excess. From determining the limiting reagent we are able to calculate the theoretical mass of the product formed. First step to find the percentage yield is to balance. The number of atoms in the reactants must be equal to the atoms in the products. This is due to the law of conservation of mass. Matter can?t be destroyed or created but transferred so therefore the chemical equation has to be balance so that the number of atoms on both side and the exact ratio of how the reactants is displayed. Second step is to find the limiting reagent. Limiting reagent is the reactant that is depended upon to determine how much of product is made. In order to find the limiting reagent the equation moles= mass/molar mass. Now that the moles are figured out, multiply the number of moles of the reactants by the ratio of the reactant and the product. ...read more.

Middle

Yellow precipitate forms again because KI is limiting. Pb(NO3)2(aq) No reaction, because Pb (NO2)3 is in excess. Testing for Limiting Reagent: Mass of dry filter paper: 1.51g Mass of PbI2: 4.16 Percentage Yield Mass with filter paper- mass of filter paper= mass of PbI2 4.16-1.51 = 2.65 Actual mass/ theoretical mass * 100% = Percentage Yield 2.65/2.78 =0.95323741 *100% = 95.3% Analysis The yellow precipitant produced was the reaction between the lead and iodine. When those two reactants reacted it undergone a double displacement and a yellow precipitant was produce in a clear solution. PbI2 was the solid produce and KNO3 was the solution left behind. There was extra solution left behind because not enough of one reactant was present for more PbI2 to form. This is the limiting reagent. When testing for the limiting reagent Pb (NO3)2 was placed into KNO3 and no reaction occurred. Whereas when KI was placed into KNO3 yellow precipitant started to form again. This proves and shows that KI was the limiting reagent and prevented more precipitant to form since there was not enough to react with Pb(NO3)2. With the percent yield it has be determined that our experiment has captured 95.3% of the PbI2 compared to the theoretical mass. ...read more.

Conclusion

The most important finding was that with theory anything can be predicted in a chemical reaction, the limiting reagent and excess reagent can be found. Through this experiment we were able to quantitatively and qualitatively determine the limiting reagent in the chemical reaction. Also compare the theoretical and actual values in order to find the percentage yield of the reaction and achieve a result that was 95% accurate to the predicted mass. A trend that occurred amongst many groups is not being able to obtain all solid and this is one of the major challenges that everyone had with this lab. Also all groups were able to predict the result that KI is limiting. Applications Limiting reagents, excess reagents, theoretical yield and percentage yield may be used in the real world. Some chemicals sold in stores may have to be experimented on to find out if there are enough of both reactants to produce a functioning chemical and efficiency of the chemicals being combined. However this may also be used in the food industry to test for how much of each ingredient is in a product or how much of an active ingredient is needed to react with the other ingredients. Experiments on limiting reagents may be used frequently in the science world however there is not much information on where and how these experiments are performed. ...read more.

This student written piece of work is one of many that can be found in our International Baccalaureate Chemistry section.