Percent Composition Of Magnesium Oxide

Topics: Magnesium, Oxide, Magnesium oxide Pages: 5 (1042 words) Published: January 17, 2015

Percentage Composition of Magnesium Oxide

Aleshia Otieno
Mr. Taylor
Lab #4
Monday, November 17, 2014

Percentage composition is the percentage of a formula mass represented by each element. Percentage composition compares the mass of one part of a substance to the mass of the whole. The law of definite proportions states that a specific compound always contains the same amount of elements in fixed proportions by mass. By finding the percent composition of magnesium oxide one will essentially be proving this law to be true.

The purpose of this lab is to determine the percent composition of magnesium oxide and determine whether the percentage is consistent.

Based on the law of definite proportions it is hypothesized that the percentage composition of magnesium oxide will be 60.3% magnesium, and 39.7% oxygen.

Hypothesis Calculations

Materials and Apparatus
8 cm strip of magnesium, Mg(s), ribbon
Small square of sandpaper or steel wool
Paper towel
Electronic Balance
Clean, dry crucible with lid
Bunsen burner
Retort stand
Ring clamp
Clay triangle
Welder’s goggles
Flint lighter
Crucible tongs
Ceramic pad

1. Observation tables were to be copied into lab books in order to record data. 2. Equipment was assembled as shown in diagram. (See figure 1.1 on page 2) 3. Welder’s goggles were used to protect the eyes when the magnesium was burning. 4. An 8cm long strip of magnesium was stripped of possible oxidation with a piece of sandpaper or steel wool. A piece of dry paper towel was used to remove any possible residue. 5. Based on the observation table the mass of the crucible with lid was recorded. A piece of magnesium was placed into the crucible with a lid and that mass was recorded as well. 6. With the lid off the crucible and the piece of magnesium strip inside, the crucible was placed onto the clay triangle. A Bunsen burner was lit to a high temperature (blue flame) with a flint lighter and placed directly under the crucible. Crucible tongs were then used to balance the lid on an angle allowing the crucible to mainly be closed while allowing little bit of oxygen into the crucible. Once the magnesium ignited the lid was placed on the crucible for a minute. 7. Crucible tongs were use to lift the side of the crucible lid in order to let in more oxygen. 8. Once the magnesium stopped igniting when exposed to oxygen Bunsen burner was turned off and crucible was left to cool. 9. A glass-stirring rod was used to make sure all magnesium reacted, and then the glass rod was cleaned using water. 10. The crucible was the placed back over flame until the water boiled off and magnesium oxide remained.

11. Crucible was removed from flame and allowed to cool for approximately 15 minutes. Mass of magnesium oxide was recorded.
12. Magnesium oxide was disposed of in a chemical waste bin.

Figure 1.1
Mass Observation Table (Table 1)
Mass of empty crucible and lid (g)
Mass of crucible, lid and magnesium (g)
Mass of crucible, lid and magnesium oxide (g)
Mass of Magnesium Oxide produced (g)
Mass of oxygen that must have reacted (g)
Percent mass of magnesium in magnesium oxide

Calculations/ Analysis/Discussion
Mass of magnesium used?
33.257g-33.192g= 0.065

Mass of magnesium oxide produced?
33.304g-33.192g= 0.112g

Calculate the mass of oxygen that reacted with the magnesium? 0.112g-0.065= 0.047

Calculate the percentage composition of magnesium oxide based on data above. Mass of Mg= 0.065g
Mass of MgO= 0.112g
Percentage composition of Mg:

Because the percentage composition of magnesium is 57.9% we can take 100% and subtract 57.9% in order to get the percentage composition of oxygen, which is 41.2%. Therefore the percentage composition of magnesium oxide based...

Bibliography: Alfredo T. "Calculating the Percentage Composition of MgO| Socratic." N.p., 9 July 2014. Web. 16 Nov. 2014.
"McGraw-Hill Ryerson EBook - Home." McGraw-Hill Ryerson EBook - Home. N.p., n.d. Web. 16 Nov. 2014.
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