Chem 102L; Due O1 March 2007, 3 p.m.
This group quiz is take-home, open book,
and depends in large part on your use of the Chem-Phys Handbook.
There are two on the lecture room's front bench, and Dr. Faile has two more.

Answer six of the following seven questions. Indicate the six by circling the questions' numbers.

  1. (5 pts) Last semester you studied the decomposition of KClO3.
    (2 KClO3 2 KCl + 3 O2)
    At what temperature does KClO3 decompose?

  2. Pretend: Having had Intro Chem years earlier, you make an astute observation on some land that you just bought, and are now putting a new road across the property. Last week's road cut has exposed a layer of white rock which you initially presumed to be limestone. You have now returned to extract some of the stone for making concrete, but you see the whiteness has disappeared and now a bluish gray exists, but after some scraping you find it is still white underneath. You get really excited, and have $$$ in your eyes.

    1. (5 pts) What is the name of the natural mineral that is AgCl?
    2. (10 pts)Write the chemical reaction that goes from white to blue-gray.


    3. (5 pts) You want to extract the silver from the ore. You remembered that lab in which AgCl was dissolved by adding NH4OH, so you try this and it works. Alas, the ammonia fumes of such a big operation are overpowering and you hope there must another way. What other aqueous solution might you use to dissolve the AgCl?

  3. (15 pts) You've had the greater part of a year's worth of chemistry and so you feel rather confident that you can help Jason with his unknown sugar even though he presents you with something you've not heard of before, but he explains it to you. If you have a polarized light source, and shine the beam at a solution of sugar, the light's plane of polarization is rotated as it passes through the solution. Jason shows you this as you adjust some dials as you compare water (no twisting of the light), and his unknown which twists the light +118 degrees (i.e.: to the right or clockwise 118 degrees after passing through 10 cm of a 1% solution) under standard conditions. He tells you that his unknown is one of these four: fructose, glucose, maltose and sucrose. Circle the one it is?

  4. (20 pts) You know that nickel sulfide, NiS, is insoluble in water, but upon addition of NH4OH, the ppt dissolves.

    1. What color is the nickel-ammonia complex?
    2. Append the correct charges in the chemical equation shown here:

      NiS + n NH3 → Ni(NH3)n + S

    3. "n" is most likely what number?

  5. (20 pts) The pH indicator phenolphthalein is colorless in acid, but is red in base. You take some powder of Ag(NH3)nCl and dissolve it in water: the pH = 7. You begin heating the solution, add a few drops of phenolphthalein, and the solution soon becomes red and ppt appears. You then cool the solution, and the color disappears and the ppt dissolves.

    1. What's happening on the chemical level?



    2. Put your prose into two chemical equations - one for heating and the other for cooling.






  6. (10 pts; right minus wrong!) Which acid in the following is stronger when in equimolar concentrations:

    AH A- + H+ (Kdis = 2)
    BH B- + H+ (Kdis = 1/2)

  7. (20 pts) You always try to be safe in chemistry, so you need to know a few dangerous compounds. Circle those of the following which are dangerous and explain why?

    1. silver azide, AgN3

    2. nitrogen tri-iodide, NI3

    3. mixing household ammonia with household bleach (sodium hypochlorite)

    4. mixing NaCN with HCl

    5. sodium metal, Na°