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Introduction

The Empirical Formula of Magnesium Oxide Experimental Design Focus Question What is the empirical formula for magnesium oxide? Hypothesis The combustion of magnesium will generate data which can be used to calculate the empirical formula of magnesium oxide. Theory The following combination reaction was used in this experiment: Magnesium + Oxygen � Magnesium Oxide The Law of Conservation of Mass can be used to determine the amount of oxygen which has reacted with a given amount of magnesium in order to produce a measured amount of magnesium oxide. These masses can then be converted into moles in order to determine the simplest molar ratio and thus the empirical formula for magnesium oxide. Variables Variables identified Type of variable Treatment Amount of magnesium used Independent variable Different groups will use different masses. Masses will be small enough to ensure that the reaction can occur without requiring the lid to be lifted too often. Mass of magnesium oxide Dependent Variable The mass of this product will be measured after it has been observed that no further reaction will occur. Container used Controlled Variable A crucible with a lid will be used in order to allow the combustion in a closed environment, preventing the loss of magnesium oxide powder. Surface area of magnesium Controlled Variable Magnesium ribbon will be used in all cases. Concentration of oxygen in the container Controlled Variable The experiments will all be performed on the same day, in the same laboratory, i.e., the atmospheric conditions and oxygen concentration will be the same. ...read more.

Middle

Percentage yield = actual mass of the product/ theoretical mass of the product * 100% Theoretical mass = number of moles of the product * molar mass According to the balanced equation: 2Mg + O2 � 2MgO, it can be deduced that 1 mole of magnesium with excess oxygen will produce 1 mole of magnesium oxide. Therefore, if n (Mg) = 0.006 mol, actual m (Mg) = 0.221g, n (MgO) = n (Mg) = 0.006 mol Theoretical mass (MgO) = 0.oo6*(24.31+16.00) = 0.247g Percentage yield = 0.221/ 0.247 * 100% = 89% Only 89% of the magnesium reacted with the oxygen. Presentation *The percentage uncertainties of the number of moles were the percentage uncertainties of the mass of each element (explained in Sample Calculation Section). The final value was the greatest percentage errors in Table 2. *The values of some of the absolute uncertainties are 0.000. This does not mean that there were no uncertainties; it was only because the uncertainties were so small that when they were rounded up to 3 decimal places, they became 0.000. *Trial 4 seemed to be anomalous. Thus, when calculating the average, the results from Trial 4 were excluded. It is noticed that Ave. of n (Mg) is 0.006 and Ave. of n (O) is 0.004; their ratio seems to be 3:2. However, all the calculations were done by Excel and rounded up to 3 decimals. As a result, the Ave. ratio calculated is 1:1. ...read more.

Conclusion

Random errors reduced: the masses of the objects will be accurate. Lid-lifting causing loss of mass of the products Random error Lift the lid every 3 minutes instead of irregular time intervals to ensure the reaction taking place thoroughly. This prevents the reactants in the crucibles from escaping. Random errors reduced; thus, a more accurate empirical formula of magnesium oxide will be gained. Experimenter's lack of experience Random error Practice the procedures to perform the experiment, i.e., increase trials (3 trials) so that the experimenter will be familiar with the method. Random errors reduced: fewer mistakes would be made during experimenting, such as weighing the masses; therefore, more accurate results, like the masses of the reagents can be obtained to draw better graphs. Precision of the balance Systematic error The balance should be calibrated regularly. The actual masses of the apparatus and reagents will be measured. No systematic errors will be involved. Weighing the actual experimenting equipment and substances Human error causing random error *In the experiment, it was required to weigh the mass of the crucible, its lid and magnesium oxide. It was observed that some of the products (white powder) left on the lid. If a different lid rather than the experimenting lid was taken to be weighed, then the results would be inaccurate because the lids have different masses. Make sure there is only one set of each apparatus so that two pieces of the same apparatus will not be mistaken. The actual magnesium oxide produced will be measured. No human errors will be involved; reduction of random error. ?? ?? ?? ?? ...read more.

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