# Is this chemistry work correct? - A level

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Thread starter 5 years ago
#1
It would be great if someone could just check over this and help me understand how to answer the rest of the question about the oxygen (don't know if they are asking you to work out the mass (I didn't think it was even possible to work out the mass of oxygen). Also am I correct in taking the average for the mass of magnesium. Thanks

1 2
Mass of crucible and lid (g) 22.71 24.78
Mass of crucible, lid and magnesium (g) 22.81 24.83
Mass of crucible lid and product (g) 22.85 22.86

Mass of magnesium for experiment 1 – 0.1g
Mass of magnesium for experiment 2 – 0.05g
Average mass of magnesium = 0.075g

Analysis of results
1.) Calculate the mass of magnesium that you reacted, the magnesium oxide formed and oxygen that reacted.
2Mg (s) + O2 (g)  2MgO (s)
Mass of magnesium reacted = 0.075g
Number of moles of magnesium = Mass / Molar mass
= 0.075/24.3 = 0.0031 mol
Number of moles of oxygen reacted = 0.0031/2 = 0.0015mol
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5 years ago
#2
Yes you are absoutely correct so far (just to clarify for you, of course gases also have a mass - all matter, solids, liquids and gases have masses, which are dependent on the molecular masses, respectively.

So, as you have correctly worked out, 0.0015 moles of oxygen were formed.

Mass of one mole of O2 = 16 X 2 = 32 g

So the mass of oxygen that reacted on average in EACH of your 2 experiments = 0.0015 X 32 = 0.048g = 48 mg

if you are still confused.com (!) about any aspect please don't hesitate to ask - i am here to help you, not to judge you!!

Mukesh
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