describe a volumetric flask and volumetric Consider the following observations:

Question

describe a volumetric flask and volumetric Consider the following observations: an unknown quantity of zinc was mixed with an unknown quantity of iodine in a test tube. Water and acetic acid were added and the contents of the tube were shaken for 20 minutes. After this time the solution in the tube was brown. Agitating the tube for an additional 10 minutes produces no lightening of the color of the solution. What is the limiting reactant in the reaction What reagent is present in excess Explain. Is it possible to determine the yield in the above expirement Why or why not A student produced ZnI_2 then allowed the product to cool to room temperature without covering the vessel. How will the percent yield be affected Will it be higher or lower than the true value Why If 2. 00 g of zinc are combined with 5.00 g of iodine and reacted according to the instruction in this lab, which reactant will be left over How much (in grams ) of the excess reagent will remain

Explanation / Answer

1) ZnI2 formed in the above reaction is a colorless liquid. The brown color lef behind is due to unreacted iodine. Hence, the reagent in excess is iodine while the limiting reagent is zinc.

2) It is not possible to determine the yield since the initial quantities of zinc and iodine are not given.

3) If the vessel is left open, then some of the I2 will be lost and the percent yield will be lower than the expected value.

4) Zn + I2 ------- ZnI2

2 gm of Zn corresponds to 2/65.38 = 0.0306 moles

5 gm of iodine corresponds to 5/253.8 = 0.0197 moles

Hence the limiting reagent is iodine.

Excess reagent is Zinc. Amt of Zn left over = 0.0306 - 0.0197 = 0.0109 moles = 0.0109 * 65.38 = 0.713 g

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