In this experiment you determined the mass of oxygen (that combined with a weigh
ID: 494496 • Letter: I
Question
In this experiment you determined the mass of oxygen (that combined with a weighted mass of magnesium) by subtraction: mass of product minus mass of original magnesium = mass of oxygen combined. As a result of this procedure, anything that was in the crucible at the end of the experiment, along with the magnesium oxide product, would cause an error in the figure that is recorded as "mass of oxygen." Would extra mass in the crucible cause the "mass of oxygen" to come out too high or low? Explain. The correct formula for magnesium oxide is MgO, a 1.0 to 1.0 ratio. But sometimes in this experiment the ratio of Mg to O comes out too low. (Example: 0.9 Mg to 1.0 O) In that case, it means that there was too much oxygen relative to the mass of magnesium. At other times it comes out that the ratio is too large, An example would be: 1.2 to 1.0 (Mg to O). In such a ease it must be that there has been too little oxygen (or too little weight at the end of the experiment, which registers as too little oxygen.) In each ease below, decide whether the situation described would lead to a calculated ratio of too much oxygen, or too little oxygen, Putting in more water than is needed and then not drying out this excess water. Having some Mg(OH)_2 left in the crucible instead of converting it to MgO. Having some Mg_3N_2 in the crucible as product, instead of pure MgO. Forgetting to weight the cover along with the crucible and contents at the end. Letting a lot of the dense white smoke escape from the crucible during the burning. Here is some data from a similar experiment, to determine the empirical formula of an oxide of tin. Calculate the empirical formula according to this data. Mass of crucible, cover, and tin sample 21.76 g Mass of empty crucible with cover 19.66 g Mass of crucible, cover, and sample after heating 22.29 gExplanation / Answer
Answer 1)
The Mass (impurity) in crucible cause "Mass of Oxygen" to come out too low.
Explanation :
a) In this experiment of determination of Oxygen mass, a fixed mass of Mg stoichiometrically react wih O2 and gives corresponding Magnesium oxide product.
b) As a part of experimental procedure first a mass of Mg taken in crucible is measured.If the crucible already contain some impurity it will also get added to mass of Mg mass. This is the mass which we will use in calculation.
c) Then this fixed known mass (considering wholely Mg only which is not actually due to impurity) react with O2 and gives product.
Say Actual mass of Mg = 'A' g Mass of Impurity = 'I' g.
Hence Wrong mass of Mg = (A+I) g.
And obviously (A+I) > A.
Let mass of product formed = 'P' g.
From this we calculate mass of Oxygen reacted as,
Apperent Mass of Oxygen reacted = Mass of product - Mass of Mg (taken wrongly) = [P - (A+I) ] g.
But Actual mass of Oxygen reacted = Mass of product - Actual mass of Mg. = [P - A] g.
As (A+I) > A
We have,
[P - (A+I)] < [P - A]
i.e. Apperent Mass of Oxygen < Actual Mass of Oxygen.
I.e. Apperent mass is low than Actual mass of Oxygen calculated.
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