A student rushed in order to complete this experiment quickly. In attempting to
ID: 854231 • Letter: A
Question
A student rushed in order to complete this experiment quickly. In attempting to save time, the student made some procedural errors. Briefly describe the effect of each of the following errors on the calculated ratio of Mg to O (indicate whether the calculated ratio would be unaffected, too high, or too low). Thoroughly explain your reasoning.
a.) The student did not heat the crucible and crucible cover to constant mass before adding Mg and carrying out the reaction.
b.) The student failed to clean the tarnished Mg ribbon with steel wool, before using the Mg.
c.) Rather than adding 6 M HCl solution dropwise as directed, the student poured 3 mL of 6 M HCl solution onto the Mg in the crucible. The solution foamed, and some material splattered out of the crucible.
d.) When transferring the crucible from the hood to the balance, the student sneezed, blowing some of the fluffly product out of the crucible and onto the floor. Because it was impossible to collect the lost solid, the student continued the experiment using the remaining product.
e.) The student decided not to heat the crucible and contents to constant mass, following the reaction of Mg with HCl solution and atmospheric O2.
Explanation / Answer
a.) If they are not heated, the moisture or humidity which presents there, adds up for the weight of Mg. But, actually the Mg weight is less, because we weight Mg+moisture. So, the calculated ratio would be too low.
b.) Before using we should clean the Mg ribbon because of the presence of any unwanted material present on it, which causes the Mg to weigh more than the actual. So, the calculated ratio would be too low.
c.) As the acid is added at a time, the reaction is not controlled and complete. This results in formation of foam and loss of material out of the crucible through splatter. This results in decreased amount of the product. So, the calculated ratio would be too low.
d.) As some of the solid is lost because of sneezing, we continue to work with less starting material, which gives less product. So, the calculated amount would be too low.
e.) If not heated, that results in extra weight of the product than the actual. This results in more yield. So, the calculated amount would be too high.
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