Conclusions The literature values listed for the unknowns in this assignment are
ID: 509952 • Letter: C
Question
Conclusions
The literature values listed for the unknowns in this assignment are from either the Merck Index or the CRC Handbook, the two most used reference handbooks. However, the values tend to vary slightly across literature sources and sometimes the temperatures are given as ranges. Give at least one reason for the variations in these reported temperatures.
In general, the boiling points of compounds increase down a group in the periodic table. The melting points and boiling points for the hydrogen compounds of group 6A elements are in the table below.
Melting Point (°C)
Boiling Point (°C)
H2O
0.0
100.0
H2S
–82.0
–60.0
H2Se
–65.7
–41.2
H2Te
–49.0
–2.2
Use your understanding of chemistry to propose an explanation for the anomaly in the trend for the hydrogen compounds of group 6A elements shown in the table below
Explanation / Answer
In H2O there is hydrogen bonding which is strong intermolecular attraction force. So H2O has higher melting and boiling points than remaining compounds.
In remaining three compounds major intermolecular forces are dipole-dipole interactions.
The order of strength of intermolecular attraction forces is
H2Te > H2Se > H2S
Among tthe hree compounds H2Te has higher melting and boiling points as it has stronger intermolecular attraction forces.
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