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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 your periodic table. 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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