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Reaction of Magnesium with Oxygen

Goal. To study stoichiometric relationships governing mass and amount in chemical formulas. . Objectives. Measure masses before and after the oxidation reaction of Mg metal and O2 gasUse masses to calculate the experimental empirical formula of magnesium oxideCompare the experimental empirical

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Reaction of Magnesium with Oxygen

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    1. Reaction of Magnesium with Oxygen

    2. Goal To study stoichiometric relationships governing mass and amount in chemical formulas.

    3. Objectives Measure masses before and after the oxidation reaction of Mg metal and O2 gas Use masses to calculate the experimental empirical formula of magnesium oxide Compare the experimental empirical formula to the theoretical empirical formula

    4. Review on Mole Concept Molecular Weight = Sum of atomic weight of all the elements in the molecule. For NaCl = 22.99 + 35.45 = 58.44 For H2O = 2 x 1.01 + 15.99 = 18.00 Molar Mass = Gram per Mole = Molecular Weight in g / mol. For NaCl = 58.44 gram / mol Mole = Mass / Molar Mass. 5 gram (of NaCl) / 58.44 gram / mol = 0.0856 mol

    5. Review on Mole Concept Number of Particles in 1 mole = 6.023 x 1023 particles. How many particle in 5 gram of H2O? Molecular weight of H2O = 18 Molar Mass of H2O = 18 g / mol Mole of 5 gram of H2O = 5 g/ 18 g/mol =0.278 mol. So number of water molecule in 0.278 mol = 0.278 x 6.023 x 1023 = 1.67 x 1023 particles

    6. Overview of Concepts Law of conservation of mass. Total mass of products must equal total mass of reactants

    7. Molecular Formula Molecular Formula Molecular Formula tells you the composition of different element in a molecule. H2O, CO2, CO, NaCl May be same as empirical CH2O is an empirical formula and molecular formula for FORMALDEHYDE. May be multiple of empirical

    8. Empirical Formulas Empirical Formula Simplest formula Agrees with elemental analysis Smallest set of whole # ratio of atoms CH2O is an example for empirical formula. Formaldehyde: HCHO Acetic Acid: C2H4O2 Lactic Acid: C3H6O3 Glucose: C6H12O6

    9. Oxygen with Metal Oxygen is almost reactive to all metals except Gold and Platinum. Picture 1 shows the product of Cu + O2 Picture 2 shows the product of Fe + O2 What kind of reaction is this???

    10. Oxidation - Reduction Also called redox reactions Oxidation - loss of electrons by an atom Reduction - gain of electrons by an atom Oxidizing agents - substances taking electrons from other substances (oxygen, chlorine) Reducing agents - supply electrons to oxidizing agents (hydrogen, carbon)

    11. Oxidation - Reduction In todays experiment, we are going to do an oxidation reduction reaction. Magnesium reacts with oxygen at high temperature.

    12. Oxidation - Reduction Magnesium will be oxidized and oxygen will be reduced You will get magnesium oxide as product. We are going to find the value of x and y from our experiment. x Mg + y O2 MgxOy

    13. Apparatus Set Up Obtain a crucible from the centre desk and clean out any loose material.

    14. Cleaning Crucible Place the crucible and lid in the clay triangle, with the lid sitting slightly ajar atop the crucible. Heat the crucible and lid with your Bunsen burner for about 5 minute. After heating, use your tongs to place the crucible and lid on your wire gauze mat and allow them to cool.

    15. Procedure Measure the mass of the crucible and lid. Then add a pre-cut (~0.5 gram) piece of magnesium ribbon to the crucible and reweigh. Place the crucible and lid back in the clay triangle and heat vigorously. Check the progress of the reaction very often. If you see any sparks or bright glow that means still the reaction is in progress and continue the heating.

    16. Procedure Keep burning the metal even after you dont see any sparks. Allow the crucible to cool on its own. Reweigh the crucible to find the mass of magnesium oxide.

    17. Calculations Mass of Magnesium = Mass Cr+lid+Mg Mass Cr+lid Mass of Magnesium Oxide = MassCr+lid+MgxOy - Mass Cr+lid Mass of Oxygen = Mass MgxOy MassMg

    18. Empirical Formula Find the mole of Magnesium. Mol Magnesium = Mass of Mg / molar mass of Mg. Find the mole of Oxygen Mol Oxygen = Mass of Oxygen / Molar Mass of Oxygen Add the lowest whole number in the places of x and y to the formula MgxOy

    19. Elemental analysis of a sample of an ionic compound gave the following results: 2.82g of Na, 4.35g of Cl, and 7.83g of O. What is the empirical formula? Number of mole each: Insert Moles as subscript Divided by the smallest number of moles Multiply by 2, 3 if you dont have the whole number

    20. 2.448 g of an iron oxide was analyzed and found to contain 1.771 g Fe and 0.6766 g O. Calculate the empirical formula. Number of mole each: Insert Moles as subscript Divided by the smallest number of moles Multiply by 2, 3 till you get whole number

    21. Precautions Dont touch the hot items with your bare hand and assume everything is hot once flames are on. Work in pairs and both of you start the trial one simultaneously. Do not look the crucible directly when you are heating.

    22. Precaution 2 Never ever cool the hot crucible with cold water. If you keep in water bath or Ice bath then you will end up with broken crucible. Let it cool on its own.

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