1. Magnesium + oxygen Empirical Formula Determination

2. 1. Determine the mass of magnesium used. (Subtract B – A) 19.06 g – 18.82 g = 0.24 g

3. 2. Determine the number of moles of magnesium used. Hint: Answer #1: x 1 mole Mg = 24.305 0.24 g 0.0099 mole

4. 3. Determine the mass of magnesium oxide formed. (Subtract C – A) 19.21 – 18.82 = 4. Determine the mass of oxygen that combined with the magnesium. (Subtract Answer #3 – Answer #1) 0.39 – 0.24 = 0. 39 g 0.15 g

5. 5. Calculate the number of moles of oxygen atoms that were used. Hint: Answer #4: 0.15 g x 1 mole O = 15.9994 0.0093 moles

6. 6. Calculate the ratio between moles of magnesium used and moles of oxygen used. Express this ratio in simplest whole number form. After dividing, round each to the nearest whole number. Divide: moles Mg = = moles O = ________ = moles Mg 0.0099 mole 0.0093 moles 1 1 0.947 1:1 ratio

7. Ratio of Mg:O is 1:1 7. Write the empirical formula for magnesium oxide. (Lowest whole number ratio of atoms) ____________ Empirical formula is the lowest whole number ratio of atoms. MgO

8. According to the charges of Mg and O what should the formula be? 1+ 2+3+ 4- 3- 2- 1- 0 Magnesium oxide Mg 2+ + O 2-  MgO 4+

9. If moles of Mg is lower than moles of O it would seem that the group could have the following errors: 1. The crucible was still wet when it was weighed. The water would have evaporated affecting the masses recorded later. 2. The magnesium strip may have not been cleaned well or had a coating of oxide already on the strip. This would make the original mass of Mg incorrect due to the added O. All error examples represent a ratio less than 1:1.

10. If moles of Mg were higher than moles of O the following errors may have occurred: 1. The sample was not heated long enough. This would result in not all of the Mg completely reacting leading to less oxygen in the MgO combustion product. 2. Some white powder was spilled or stuck to the tongs. This would show the final mass lower than normal and since oxygen was calculated by subtracting Mg from final mass the O would have been less. 3. The sample lost some mass when smoke escaped. All error examples represent a ratio greater than 1:1.