## Tuesday, May 17, 2011

### Final Exam Review: #20 and #31

20) A white powder is analyzed and found to contain 43.64% phosphorous and 56.36% oxygen by mass. The compound has a molar mass of 283.88 g/mol. What are the compound's empirical and molecular formulas?

$43.64 g P*\frac{1 mol P}{31.0 g P}=1.41molesP$
$56.36gO*\frac{1 mol O}{16.0 g O}=3.52 moles O$
$P_{1.41}O_{3.52}=P_{1}O_{2.5}=P_{2}O_{5}=empirical formula$
$2(31.0)+5(16.0)=142.0$
$\frac{142.0}{283.88}=\frac{1}{2}$
$empirical formula*2=molecular formula=P_{4}O_{10}$

31) A topic not covered by the final exam review is how a nuclear reactor works:
A nuclear reactor is basically a system of recycled water. The water is heated and is turned into steam which travels down a steam line to spin the blades of a turbine. The turbine then turns the shaft of a huge generator, where electricity is produced. The steam then cools down back into water and the cycle repeats. Control rods prevent the reactor from overheating and when they and the fuel rods are spent they are placed in a cooling tank called a "swimming pool".

#### 1 comment:

1. Very good! I agree with your responses but I would like to elaborate on your chosen response for 31. Basically, a nuclear reactor relies on fission to create energy. Bombarding particles hit the nuclei of the target particles, therefore releasing some amount of energy. The control rods prevent the reactor from overheating because they are used to absorb neutrons. They are inserted to slow down the fission because they absorb more neutrons and therefore more energy and they are taken out to speed up the reaction.