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Chemistry Practice Problems for Non Technical Majors
Typology: Exercises
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Section 1: 1.1 Define mole, Avogadro’s number, GAW, and GFW. In 500 grams of Na PO 3 4 , how many grams and moles of each constituent element are there? Mole: 6.02 x 10 23 atoms (or molecules, etc.) Avogadro’s number: 6.02 x 10 23 atoms in X grams of any element, where X is the atomic weight of the element GAW: Gram Atomic Weight, the mass of one mole of atoms GFW: Gram Formula Weight, the mass of one mole of molecules
The GFW of Na PO 3 4 is: (3x22.99 + 30.97 + 4x15.999)g = 163.94 grams
500 g Na PO 3 4 1 mole 163.94 g
For each mole of Na PO 3 4 , there are 3 moles of sodium (Na atoms), 1 mole
of phosphorus (P atoms), and 4 moles of oxygen (O atoms) according to the chemical formula. Therefore:
3.05 moles Na PO 3 4 3 moles Na 1 mole Na PO 3 4
9.15 moles Na 22.99 g Na 1 mole Na
3.05 moles Na PO 3 4 1 mole P 1 mole Na PO 3 4
3.05 moles P 30.97 g P 1 mole P
3.05 moles Na PO 3 4 4 moles O 1 mole Na PO 3 4
12.20 moles O 15.999 g O 1 mole O
Double-check the math by adding the results found for masses of the three constituent elements in Na PO : 3 4 210.4 g + 94.5 g + 195.2 g = 500.1 grams
(within roundoff of 500 g)
= 3.05 moles Na PO 3 4
= 9.15 moles Na
= 210.4 grams Na
= 3.05 moles P
= 94.5 grams P
= 12.20 moles O
= 195.2 grams O
1.2 State the three classes of elements. Give several examples for each. What is a period on the periodic table? What is a group on the periodic table? What do each of these classifications indicate about the elements within them? Metals: Na, Mg, Sn, Mn, Co, among others Non-Metals: C, N, Br, Kr, among others Semi-Metals: B, Si, Ge, As, Sb, Te, Po, At
Period: horizontal row on the Periodic Table, indicates the number of electron shells Group: vertical column on the Periodic Table, indicates the number of electrons in the outer shell (and thus similar chemical properties)
1.3 Given one neutral atom of magnesium, state the following:
atomic weight 24.312 amu class of element metal period 3rd group IIA other elements with similar properties Be, Ca, Sr, Ba, Ra
1.4 Given that every atom of neutral calcium has two electrons in its outer shell, how many electrons does magnesium have in its outer shell? Why? 2, because Mg is in the same group as Ca.
Section 2: 2.1 Describe the differences between ionic bonds and covalent bonds.
2.7 How many grams of SO 2 would be produced in the preceding reaction from 200 g of CS 2 assuming a sufficient amount of O 2 is available?
200 g CS 2 76.139 GFW CS 2
2.6268 moles CS 2 2 moles SO 2 64.062 g GFW SO (^2) 1 mole CS 2 1 mole SO (^2)
2.8 Balance the following reaction equation:
2 Cr 2 O 3 + 3 O 2 + 4 H 2 O → 4 H 2 CrO (^4)
2.9 If 50 grams of H 2 CrO 4 were produced when the preceding reaction took place in 0.5 liters of water, what was the molarity of the original Cr 2 O 3?
50 g H 2 CrO 4 1 mole H 2 CrO 4 2 moles Cr 2 O (^3) 118.008 g H 2 CrO 4 4 moles H 2 CrO (^4)
0.212 mole Cr 2 O (^3) 0.5 liter H 2 O
Section 3:
3.1 State the problems associated with uncontrolled corrosion in a reactor plant.
3.2 State what happens to a metal during the oxidation step of a REDOX process. What might be the visible changes in the metal?
= 2.6268 moles CS 2
= 336.56 g SO (^2)
= 0.424 M Cr 2 O (^3)
= 0.212 mole Cr 2 O (^3)
3.3 Define passivity. Passivity is the buildup of a stable, tenacious layer of metal oxide corrosion products on the surface of a metal that act as a barrier separating the metal surface from the environment, thereby impeding further corrosion.
3.4. Describe how the rate of corrosion is affected by temperature, oxygen, pH, and metal composition.
3.5 Identify and describe the action taken for the initial fill of a reactor system to minimize corrosion.
3.6 Define crud. List five problems associated with the presence or release of crud into the reactor coolant. List the causes of a crud burst.
dissolves, and the process continues. This results in the formation of a pit inside the crevice.
3.11 Answer Question 3.8 for chloride stress corrosion cracking (SCC).
3.12 Answer Question 3.8 for caustic stress corrosion cracking.