# Chemistry 11 - DOC by Oe16Avx

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```									                              Chemistry 11 – Unit 3

Lab Percentage Composition of Magnesium Oxide

Name: _________________________

Prelab : Determine the percentage composition of magnesium and oxygen in MgO from

Purpose: To determine the percentage composition of Mg and Oxygen by mass and
determine the empirical formula.

Procedure and materials:

Data Table and Calculations

Mass of crucible and lid                              22.47    +0.01g

Mass of crucible, lid and magnesium                   22.75    +0.01g

Mass of crucible, lid and magnesium oxide             22.93     +0.01g

Mass of magnesium oxide produced                      0.46      +0.01g

Mass of magnesium that reacted                        0,28       +0.01g

Mass of oxygen that reacted with magnesium      ______0.18________ +0.01g
Discussion and Analysis—show all work and use correct sig figs.
1. Find the percentage composition of magnesium and oxygen from your data include
uncertainty:

Mass of Mg = __________________
Divided by                X 100%      = ___________ % Mg
Mass of MgO = ________________

Mass of Oxygen = _______________
Divided by               X 100% = ______________% O
Mass of MgO = ________________

2. Find the percentage error for each of the above from the calculated values from your
periodic table.(Actual-Observed)/(Actual) x100 = % error

Percentage error for Mg

Percentage error for Oxygen

3. Calculate the empirical formula of the compound using your masses from the data
table..
Use the three steps.                        Find moles                  ratio

A. Mass of Mg = __________

B. Mass of oxygen= _________

C. Empirical formula = _______________

4. When an electric current is passed through 60.0mL of water, a total of 53.33 grams of
oxygen gas and 6.67g hydrogen gas are produced before all the water is decomposed.
Calculate the percentage by mass of oxygen and hydrogen in water.

Conclusion
State all your results with uncertainty and percentage error and empirical formula.
Compare your results with predicted values.

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