The Science of Geocaching (Dunedin, Otago) Mystery Cache

A serious crime has been committed.  The Mad Scientists secret cache that contains the instructions for every alchemists dream of turning elements to gold has been stolen.  After all the clues have been compiled the crime can still not be solved.  There is one remaining clue that holds a solution to the mystery.  The crime lab has analysed the clue found at the scene.  It was too difficult for super computers to solve so they are recruiting the help of cache extraordinairs.  Answer the Redox clues below and crack the code to find the location of the mad scientists secret cache.

Find the oxidation number of the bold element in the following:

1.       H₂S

2.       H₂SO₄

3.       PO₄^3-

4.       CO₃^2-

5.       H₂O₂

6.       HClO₄

7.       Cl₂O

8.       HNO₂

Determine the elements that have been oxidised in each of the following reations:

9.       2Mg + O₂ à 2MgO

10.   Cl₂ + 2l^- à I₂ + 2Cl^-

11.   2MnO₄^- + 5H₂S + 6H⁺ à 5S + 8H₂O + 2Mn²⁺

12.   2SnCl₂ + 4HCl + O₂ à 2SnCl₄ + 2H₂O

13.   H₂SO₄ + 2HBr à SO₂ + Br₂ + 2H₂O

Determine the elements that have been reduced in each of the following reactions:

14.   2MnO₄^- + 3H₂O₂ à 2MnO₂ + 2H₂O + 3O₂ + 2OH^-

15.   Fe₃O₄ + 4C à 4CO + 3Fe

16.   C + O₂ à CO₂

17.   Mg + 2HCl à MgCl₂ + H₂

18.   Cr₂O₇^2- + 8H+ + 3SO₃^2- à 2Cr³⁺ + 3SO₄^2- + 4H₂O

Which of the following species is the oxidant?

19.   Mg + Cl₂ à Mg⁺² + 2Cl^-

Which of the following species is the reductant?

20.   Cu + MnO₄^- à Cu²⁺ + Mn<sup>2+

Code:</sup>

Example: the answer to question 19 is Cl_2, so therefore everywhere Cl₂ appears replace it with the letter “M”