Precision, Accuracy & Periodicity
Questions:

A) Two students report the following data for the density of an unknown metal:

Student 1
Deviation
Student 2
Deviation
Trial 1
22.0 g/cm3
+0.1
23.0 g/cm3
+1.1
Trial 2
21.8 g/cm3
-0.1
21.0 g/cm3
-0.9
Trial 3
22.0 g/cm3
+0.1
21.3 g/cm3
-0.6
Trial 4
21.8 g/cm3
-0.1
22.3 g/cm3
+0.4
Average
21.9 g/cm3
+/- 0.1
21.9 g/cm3
+/- 0.8
        Should both students receive the same grade? Explain your answer.
B)  In the early 1870's, Mendeleev predicted three "new" elements, their atomic masses and their densities: "Ekaboron", atomic mass = 44, ; "Ekaaluminium", atomic mass = 68, density = 5.9 g/cm3 and "Ekasilicon", atomic mass = 72, density = 5.5 g/cm3.
 
1) Identify the three elements by their modern names from their masses and relative locations in the periodic table.
2) Calculate Mendeleev's % error in his predicted density of ekaluminium and predicted density of ekasilicon versus their currently accepted values: 5.904 g/cm3 and 5.323 g/cm3 respectively.
3) A student was hired by a large international baseball bat manufacturer to determine the density of a sample of "ekaboron" oxide. The student's experimental results are shown below.
g/cm3
Trial 1
3.85
Trial 2
3.78
Trial 3
3.82
a) Write the molecular formula for the oxide. ( The element's valence is +3. )
b) Name the oxide by current IUPAC nomenclature rules.
c) What value for the density should be reported?
d) What is the student's relative precision?
e) If the accepted value for the density of the compond is 3.80 g/cm3, what is the student's error?
 
Extra credit: The NCAA (National Collegiate Athletic Association) controls the performance of baseball bats. The NCAA had considered banning the use of "ekaboron" completely in bat manufacture. Why?

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