Mg and O lab
how will the relative number of moles of mg and o be affected if the following procedural errors are made?
a)crucible is not brought to constant mass before the Mg is added.
b)water is not added after the first heating of Mg, and the entire solid in the crucible is considered to be MgO
c)some of the fluffy white ppt is lost before the crucible is weighed for the last time.
d)in an effort to begin a second sample while the first is cooling, the hot crucible containing the solid from determination 1 is accidently dropped, and a small chip is lost from the crucible.
i said b was a higher value for O because the mass of our product would be higher and we determined the mass of O by subtracting our mass of Mg used, in a previous calculation
i said the decrease in the amount of O for part c because of basically the same reason; we have a smaller product so we would calculate a smaller amount of O
the other two i'm not sure of and am kind of confused.
if you could check mine and help me with the others?
please be specific!thanks!
Sure, I'd be happy to help! Let's go through each scenario and determine how it affects the relative number of moles of Mg and O:
a) If the crucible is not brought to a constant mass before the Mg is added, it means that any mass change observed after heating may not solely be due to the formation of MgO. It could be due to residual moisture or impurities in the crucible. This procedural error would affect the accuracy of the determination of Mg and O, but it wouldn't necessarily affect the relative number of moles of Mg and O.
b) If water is not added after the first heating of Mg, and the entire solid in the crucible is considered to be MgO, this would indeed result in a higher value for O. This is because the mass of the product (MgO) would be higher due to the additional mass of the unreacted Mg. Since you calculate the mass of O by subtracting the mass of Mg used, this error would lead to a higher mass of O.
c) If some of the fluffy white precipitate (MgO) is lost before the crucible is weighed for the last time, this would result in a decrease in the amount of O. As you correctly mentioned, since the mass of the product (MgO) is smaller, you would calculate a smaller amount of O.
d) If the crucible containing the solid from determination 1 is accidentally dropped and a small chip is lost from the crucible, this would only affect the accuracy of the mass determination, not the relative number of moles of Mg and O. The loss of a small chip would not have a significant impact on the overall calculation of the moles of Mg or O.
Overall, your reasoning for scenarios (b) and (c) is correct. Scenarios (a) and (d) would not directly affect the relative number of moles of Mg and O.
Your explanations for parts a and c are correct. Here are the explanations for the other two parts:
b) If water is not added after the first heating of Mg and the entire solid in the crucible is considered to be MgO, it would lead to an inaccurate determination of the relative number of moles. The mass of the solid obtained would be higher than the actual mass of MgO because it includes the mass of any impurities or excess Mg that did not react with oxygen. As a result, the calculated number of moles of MgO would be higher than the actual number of moles of MgO. Therefore, the relative number of moles of Mg would be lower than the relative number of moles of O.
d) If a small chip is lost from the crucible when it is accidentally dropped, it would lead to a decrease in the mass of the solid obtained. As a result, the calculated number of moles of MgO would be lower than the actual number of moles of MgO. Therefore, the relative number of moles of O would be higher than the relative number of moles of Mg.
Let's analyze each procedural error and discuss how it would affect the relative number of moles of Mg and O:
a) If the crucible is not brought to constant mass before the Mg is added, it means that the initial mass of the crucible is not accurately determined. This error would result in an incorrect mass of MgO at the end of the experiment because the initial mass of the crucible is used to calculate the mass of the product (MgO). Consequently, the calculated relative number of moles of Mg and O would be inaccurate.
b) If water is not added after the first heating of Mg, and the entire solid in the crucible is considered to be MgO, this would lead to an overestimation of the mass of MgO. Since water is required to react with Mg during the combustion process and form MgO, omitting water would result in unreacted Mg being considered as MgO. As a result, the calculated mass of O would be higher than it should be, causing an overestimation of the relative number of moles of O.
c) If some of the fluffy white precipitate (MgO) is lost before the crucible is weighed for the last time, the measured mass of MgO would be lower than the actual mass. This loss of product would lead to a decrease in the calculated mass of O, resulting in a lower relative number of moles of O.
d) In this case, where a small chip is lost from the crucible, the mass of the crucible and the solid would be lower than the actual values. Since the mass of the crucible is used to calculate the mass of both Mg and O, this error would result in an overall decrease in the calculated masses of both elements. As a consequence, the relative number of moles of both Mg and O would be lower.
So, your analysis for errors b and c is correct. Error b would indeed result in a higher value for O, and error c would decrease the amount of O. However, error a would affect both Mg and O, whereas error d would decrease the amount of both Mg and O.