A historian discovers a nineteenth-century notebook in which some observations,

Question

A historian discovers a nineteenth-century notebook in which some observations, dated 1822, were recorded on a substance thought to be a new element. Here are some of the data recorded in the notebook: "Ductile, silver-white, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: 153 ?C. Density: 7.3 g/cm3. Electrical conductivity: 20% that of copper. Hardness: About 1% as hard as iron. When 4.20 g of the unknown is heated in an excess of oxygen, 5.08 g of a white solid is formed. The solid could be sublimed by heating to over 800 ?C."

A) Using information in the text and the CRC Handbook of Chemistry and Physics, and making allowances for possible variations in numbers from current values, identify the element reported.

B) write a balanced chemical equation for the reaction with oxygen

C) judging by figure 7.1 might the nineteenth century investigator been the first to discover the new element

Explanation / Answer

Firstly, the eqn: M + O2---> MxOy (not balanced)

moles O = (5.08-4.20) g / atwt O g/mole = (0.055 moles)
normal range of metal oxides are: M2O, MO, MO2, M2O3

for M2O: AW of M = (4.20g) / (2*0.055 moles) = 38 K Potassium
for MO: AW of M = 4.20 g / 0.055 moles = 76 As/Se Arsenic/Selenium
for MO2: AW of M = 4.20 g / (2*0.055 moles) = 152 (Eu) Europium
for M2O3: AW of M = 4.20 g / (2/3*0.055 moles) =114 (In) Indium

Check to see which fits these properties -- It is Indium
Ductile, silver-white, metallic looking.
Softer than lead.
Unaffected by water.
Stable in air.
Melting point:153 degrees celsius.
Density: 7.3g/cm^3.
Electrical conductivity: 20% that of copper.
Hardness: about 1 % as hard as iron.

Data from http://en.wikipedia.org/wiki/Indium
Density (near r.t.) 7.31 ?g

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