1. As pure elements, all of the halogens are diatomic molecular species. Their m
ID: 797331 • Letter: 1
Question
1. As pure elements, all of the halogens are diatomic molecular species. Their melting points are: F2, 85 K,
Cl2, 239 K, Br2, 332 K, and I2, 457 K. Using the Periodic Table, predict as best you can the molecular
formula of elemental astatine,At, the only radioactive element in this family. Also predict whether it will
be a solid, liquid, or gas at room temperature.
Elemental formula: ____________ Phase at room temperature: _____________
2. Substances A, B, and C can all act as oxidizing agents. In solution,A is green, B is yellow, and C is red. In
the reactions in which they participate, they are reduced to A?, B ?, and C ? ions, all of which are colorless.
When a solution of C is mixed with one containing B? ions, the color changes from red to yellow.
Which species is oxidized? _____________
Which is reduced? _____________
When a solution of C is mixed with one containing A ? ions, the color remains red.
Is C a better oxidizing agent than A? _____________
Is C a better oxidizing agent than B? _____________
Arrange A, B, and C in order of increasing strength as an oxidizing agent.
3. You are given an unknown, colorless, solution that contains one of the following salts: NaA, NaB, NaC.
In solution, each salt dissociates completely into the Na + ion and the anion A ?, B ?, or C ?, whose
properties are given in Problem 2. The Na + ion is effectively inert. Given the availability of solutions of
A, B, and C, develop a simple procedure for identifying the salt that is present in your unknown.
Explanation / Answer
1
The common trend is as you go down the list of halogens in order of increasing atomic number, the bond strength and melting point both increase.
Astatine would be the highest since it is after I2, and because the bond strength will be so strong, and the melting point so high, at room temperature there won't be enough kinetic energy to turn Astatine into a liquid or a gas. (It's a solid)
2
Provided information :
A is an oxidizing agent .
A ( Green Color in Solution ) can be reduced to A- Ion ( Colorless )
C is an oxidizing agent .
C ( Red Color in Solution ) can be reduced to C- Ion ( Colorless )
A ( Green Solution ) + C- ( Colorless Solution ) ----> " Red Solution "
Conclusions :
The reaction is . . . .
A ( Green Color in Solution ) + C- ( Colorless in Solution ) ---->
A- ( Colorless in Solution ) + C ( Red Color in Solution )
A is reduced __ to __ A- Ion
( Green Color disappears from Solution )
C- Ion is oxidised __ to __ C
( Red Color develops in Solution )
A is a stronger oxidising agent than C
3
Step 1, Add a drop of B to a sample of the solution. If it does not oxidize the unknown, then the unknown is NaB. If it does oxidize the unknown, then the unknown could be NaA or NaC.
Step 2, Add a drop of A to another sample of the solution. If it does not oxidize the unknown, then the unknown is NaA., if it does, the sample is NaC.
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