2SCS #1-12, p. 180

1) State the law of conservation of matter.

The law of conservation of matter is that matter is neither created nor destroyed.

2) What is a scientific law?

Scientific law summarizes what has been learned by careful observation of nature.

3) Why are expressions such as "using up" and "throwing away" misleading, if the law of conservation of matter is taken into account?

Expressions such as "using up" and "throwing away" are misleading because according to the law of conservation of matter, molecules can be converted and decomposed by chemical processes, but atoms are forever, and are not "used up" or "thrown away."

4) Complete atom inventories to decide if each of these chemical expressions is balanced.
a. the preparation of tin (II) fluoride, a component of some toothpastes (called stannous fluoride in some ingredient lists):
Sn(s) + HF(aq) --> SnF2(aq) + H2(g)
b. the synthesis of carborundum for sandpaper:
SiO2(s) + C(s) --> SiC(s) + CO(g)
c. the reaction of an antacid with stomach acid (hydrochloric acid):
Al(OH)3(s) + 3 HCl(aq) --> AlCl3(aq) + 3 H2O(l)

a. Not balanced.
Reactant side: Sn, 1; H, 1; F, 1
Product side: Sn, 1; H, 2; F; 2
b. Not balanced.
Reactant side: Si, 1; O, 2; C, 1
Product side: Si, 1; O, 1; C, 2
c. Balanced.
Reactant side: Al, 1; O, 3; H, 6; Cl, 3
Product side: Al, 1; O, 3; H, 6; Cl, 3

5) Consider this equation: N2(g) + 3 H2(g) --> 2 NH3(g)
a. What is the coefficient for hydrogen gas?
b. What is the coefficient for NH3 gas?
c. What is the coefficient for nitrogen gas?

a. The coefficient for hydrogen gas is 3.
b. The coefficient for NH3 gas is 2.
c. The coefficient for nitrogen gas is 1.

6) For each of the following processes, draw a representation of the chemical statement, balance the representation, and verify your answer.
a. preparing tungsten from one of its minerals:
_WO3 + _H2 --> _W + _H2O
b. heating lead(II) sulfide in air:
_PbS + _O2 --> _PbO + _SO2
c. rusting (oxidation) of iron metal:
_Fe + _O2 --> Fe2O3

See drawings on paper.
a. 1 WO3 + 3 H2 --> 1 W + 3 H2O
b. 2 PbS + 3 O2 --> 2 PbO + 2 SO2
c. 4 Fe + 3 O2 --> 2 Fe2O3

7) Balance each of these chemical expressions.
a. preparing phosphoric acid (used in making soft drinks, detergents, and other products) from calcium phosphate and sulfuric acid:
_Ca3(PO4)2 + _H2SO4 --> _H3PO4 + _CaSO4
b. completely burning gasoline:
_C8H18 + O2 --> _CO2 + _H2O

a. 1 Ca3(PO4)2 + 3 H2SO4 --> 2 H3PO4 + 3 CaSO4
b. 2 C8H18 + 25 O2 --> 16 CO2 + 18 H2O

8) A student is asked to balance this chemical expression:
Na2SO4 + KCl --> NaCl + K2SO4
The student decides to balance it this way:
Na2SO4 + K2Cl --> Na2Cl + K2SO4
a. Complete an atom inventory of the student's answer. Are the atoms conserved?
b. Did the student create a properly balanced chemical equation? Explain.
c. If your answer to Question 8b is no, write a correctly balanced equation.

a. Yes.
Reactant side: Na, 2; S, 1; O, 4; K, 2; Cl, 1
Product side: Na, 2; S, 1; O, 4; K, 2; Cl, 1
b. No, when balancing equations, subscripts remain the same, but coefficients are altered to balance the equation.
c. 1 Na2SO4 + 2 KCl --> 2 NaCl + 1 K2SO4

9) If you could spend a billion dollars (10 x 10^9 dollars) per second, how many years would it take to spend one mole of dollars?

If you could spend a billion dollars (10 x 10^9 dollars) per second, it would take 400,000 seconds to spend one mole of dollars?

10) Find the molar mass of each of the following substances:
a. oxygen gas, O2
b. ozone, O3
c. limestone, CaCO3
d. a typical antacid, Mg(OH)2
e. aspirin, C9H8O4

a. 32g
b. 48g
c. 100g
d. 58g
e. 180g

11) How can samples of 63.6g copper metal and 23.0g sodium metal with different masses, volumes, and densities, both correctly represent 1.00 mol of substance?

For each element, its atomic mass equals the weight of one atom in 1.00 mol0. of its substance. Therefore, although copper and sodium have different masses, volumes, and densities, the weight of each atom per mole remains the same.

12) A major advantage of the mole concept is that it enables a chemist to "count by weighing." If one mole of potassium metal has a mass of 39.1g,
a. how many atoms are in 39.1 g potassium
b. how many atoms are in 19.55 g potassium?
c. how many atoms are in 3.91 g potassium?
d. how many atoms are in 1.0 g potassium?

a. 1 atom.
b. 0.5 atoms.
c. 0.1 atoms.
d. about 0.03 atoms.