Topic: Determining the Empirical Formula of Magnesium Oxide
11 CHEM 11
Table of contents
- 5.1 Qualitative Observations
- 5.2 Example Calculations for each Calculated Value 5-7
-5.21 Experimental Values and Associated Errors
- 5.3 Accumulated Raw Data
- 5.4 Mean Experimental Values and Associated Errors
8 - 5.5 Accumulated Calculated Values, Mean Values and
9 6.0 Conclusion
- 7.1 Comparison of Errors
- 7.2 Experimental Sources of Error
The purpose of this experiment was to determine the empirical formula of magnesium oxide.
The empirical formula also known as the chemical formula is the simplest molar combining ratio of elements in a compound. Thus, if to understand the behaviour of a chemical compound we must know its chemical formula. The molecular formula is the same as or a multiple of the empirical formula, and the actual number of atoms of each type in the compound. The ratio can be determined if the mass of the individual elements, in this case magnesium and oxygen, is known in a known mass of the compound. For example:
To verify the empirical formula of magnesium oxide was to compare the masses of pure magnesium solid prior to any reaction and magnesium oxide solid after a reaction between all of the magnesium and oxygen from the air when heated from a Bunsen burner in a crucible. The concept of the mole will lead to determining the empirical formula of magnesium oxide.
In this experiment, after a known mass of magnesium is combusted, the product will consist of magnesium oxide and smaller amounts of magnesium nitride. Water will convert the nitride to magnesium hydroxide with the liberation of ammonia. Heat will cause the conversion of hydroxide with the loss of gaseous water.
In conducting this experiment we also need to take into account of errors in the experiment.
First of the errors is the Predicted Error or P.E. predicted error is the error that can be predicted for a measurement. It can be predicted from the uncertainty of the measuring instrument. For all instruments they all have an uncertainty which has a limit to the precision. The P.E formula for calculations is:
The P.E is always measured as a percent. It can also be calculated as for a value calculated by adding or subtracting two measurements made on the same instrument using the following formula:
The predicted error itself is also calculated from several measured values using the following formula:
Total P.E. = P.E. Value1 + P.E. Value2 +...…………
So in brief, predicted error is an expression of how much the experimental value might vary due to the properties of the instrument or instruments used to obtain the value.
The next type of error we have is Random Error. Random Error is when a measurement is made a number of times and an error occurs. In short, Random Error is showing how much the experimental value might vary due to one or more factors also called sources of random error operating randomly while measurements were made. The random error is also calculated as a percent of the experimental value. It is calculated with the following formula:
The final error is Experimental Error. Experimental Error is an indication of how accurate the procedure was in determining the value of the quantity. Basically it is best calculated, for the intention of judging the legitimacy of the experiment, using the mean value of a number of determinations of the same amount. Like the other two errors it is calculated as a percent of the known value. It is calculated with the formula:
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