1. Borax is Na₂[B₄O₇]10H₂O. What is the mass percent of water in borax?
How many pounds of borax contain 5.00 lb boron?

Molwt borax = 2(23) +4(11) + 7(16) +10(18) = 382
Therefore 4(11) lb B in 382 lb borax
44/382 = 5/x
x = 5(382)/44 = 43.41 lb

2. If you were interested only in the mass of the metal contained, which compound would be the cheapest source of gold:
AuI at $75.00 per 5g or Au₂O₃ at $25.00 per g. ?

Molwts: AuI = 197+127 = 324 Au₂O₃ = 2(197) + 3(16) = 442
324 g AuI has 197 g Au 442 g Au₂O₃ has 2(197) g Au
197 g Au costs 324(75)/5 = $4860 394 g Au costs 442(25)/1 = $11,050
or $24.67 per gram or $28.04 per gram
AuI is cheaper source
 

3. A 4.60-mg sample of a new enzyme found to contain manganese was treated with a strong oxidizing agent and all of the Mn was converted to potassium permanganate. The mass of KMnO₄ obtained was 2.75µg.
What is the percent of Mn in the enzyme?

KMnO₄ = 39+55+4(16) = 158
158 µg KMnO₄ contains 55 µg Mn
158/55 = 2.75/x
x = 2.75(55)/158 = 0.96 µg Mn in 4.60 mg enzyme
percent Mn in enzyme = 100(0.95 x 10^-6)/(4.60 x 10^-3) = 0.021%

If there is only one Mn atom in each enzyme molecule, what is the molecular weight of the enzyme?

100 g enzyme contains 0.021 g Mn
M g enzyme contains 55 g Mn
M = 100(55)/0.021 = 262,000 = 2.62 x 10⁵

4. What is the mass of 15 nmol of tetraphosphorus heptasulfide?

P₄S₇ = 4(31) + 7(32) = 348
15 nmol = 15(348) = 5220 ng = 5.22 µg

5. The pale yellow liquid, nicotine, is a compound containing 74.03% C, 8.70% H, and 17.27% N. Determine the empirical formula of nicotine.

In 100 g cpd: 74.03/12 = 6.17 mol C
8.70/1 = 8.70 mol H
17.27/14 = 1.23 mol N
Ratio C 6.17/1.23 = 5.01: H 8.70/1.23 = 7.07: N 1.23/1.23 = 1
Formula is C₅H₇N

6. How many grams of carbon are contained in 5.00 mL bromoform (CHBr₃), a liquid with density 2.9035 g.mL^-1?
.
. 5.00 mL x 2.9035 g/mL = 14.52 g = 14.52/(12+1+3(80)) = 0.0574 mol CHBr₃
. 0.0574 mol C = 0.0574(12) = 0.689 g

7. Ca(MnO₄)₂ + 16 HBr -->5 Br₂ + CaBr₂ +2 MnBr₂ + 8 H₂O
How many grams of Ca(MnO₄)₂ are needed to produce 5.00 g Br₂?

1 mol Ca(MnO₄)₂ = 40+2(55+64) = 278 g gives 5 mol (= 5(2)(80)) = 800 g Br₂
278/800 = x/5.00
x = 5.00(278)/800 = 1.74 g

8. What mass of SO₂ is produced when 16.25 g thiophen, C₅H₅S, is burned in excess oxygen?

4C₅H₅S + 29O₂ -> 20CO₂ + 10H₂O + 4SO₂
1 mol thiophen gives 1 mol SO₂
(5)(12)+5+32 = 97 g gives 32+2(16) = 64 g SO₂
97/64 = 16.25/x
x = 64(16.25)/97 = 10.72 g

9. A solution containing 5.00 g AgNO₃ is mixed with a solution containing 12.50 g CaCl₂. A white precipitate of AgCl is formed. What is the mass of the AgCl formed? Which is the limiting reagent, AgNO₃ or CaCl₂?
.
. 2AgNO₃ + CaCl₂ -> 2AgCl + Ca(NO₃)₂
. 5.00 g AgNO₃ = 5.00/(108+14+48) = 0.0294 mol
. 12.50 g CaCl₂ = 12.50/(40 +2(35.5)) = 0.1126 mol
. Limiting reagent is AgNO₃; mass of AgCl formed is 0.0294 mol = 0.0294(108+35.5) = 4.22 g

10. Which of the following are intensive properties of a substance?
Color, mass, volume, electrical conductivity
color, electrical conductivity

11 Name the following : Ca₃N₂, Pb(ClO)₂, S₂Cl₂, OF₂, Mn(MnO₄)₂

calcium nitride, lead (or plumbous) hypochlorite, disulfur dichloride, oxygen difluoride, manganese permanganate

12. Write formulas for the following
magnesium chlorate, ferrous chloride, mercurous nitrate, diboron hexahydride, bromine pentafluoride

Mg(ClO₃)₂, FeCl₂, Hg₂(NO₃)₂, B₂H₆, BrF₅

13. For each of the following provide the number of protons and neutrons in the nucleus, and the number of electrons surrounding the nucleus. (Periodic Table available). [mass numbers should have been given for you to be able to answer this question!]

²⁸Si, 14p+14n+14e
⁴⁵Sc, 21 24 21
⁷⁹Se^2- 34 45 36,
⁸⁸Sr²⁺, 38 50 36
¹²¹Sb³⁺51 70 48,
an alpha-particle 2p+2n+0e

14. Describe the experiment that led to the conclusion that atoms contain a very small nucleus with most of the atomic mass. With which scientist is this experiment associated?

. A beam of alpha-particles directed at a thin sheet of gold. Most pass through without being deflected; some are deflected through small or large angles following collision with the nuclei of the gold atoms. Ernest Rutherford

15. How may alpha-, beta-, and gamma-radiation be distinguished experimentally?

. Effect of electric field. alpha-particles are attracted to negative pole, beta-particles are attracted to positive pole, gamma-radiation is unaffected.

16. You are given a white powder in the laboratory. Describe three experiments that you could carry out to determine whether the powder was a mixture or a pure substance.

Examine microscopically to see if powder appears uniform.
Add solvent (water) to see if part of the powder is soluble and part insoluble.
Heat powder; if a mixture, one component may melt or may sublime, and the other component may not be affected.

17. Define "mole", "density", and "isotopes"

Mole: The quantity of a substance whose mass in grams equals the substance's molecular weight; also = 6.02 x 10²³ molecules
Density: Mass per unit volume
Isotopes: Atoms with the same number of protons in the nucleus, but with different numbers of neutrons.

18. Write a chemical formula that illustrates each of the following:
a binary molecular compound CaCl₂
a polyatomic cation NH₄⁺
an electrolyte KBr

19.    Write and balance chemical equations for the following reactions
(A) combustion of powdered aluminum metal in chlorine gas
2Al + 3Cl₂ -> 2AlCl₃
(B) the direct combination of lead with sulfur
Pb + S -> PbS
(C) the decomposition of cupric nitrate to form copper(I) oxide, nitrogen dioxide, and oxygen gas
4Cu(NO₃)₂ -> 2Cu₂O + 8NO₂ + 3O₂
(D) the combustion of dimethylsulfoxide (CH₃)₂SO in oxygen
(CH₃)₂SO + 4O₂-> 2CO₂ + 3H₂O +SO₂
(E) the decomposition of ammonium nitrite to form water and nitrogen gas
` NH₄NO₂ -> N₂ + 2H₂O

20.    Write formulas for:
mercury(I) carbonate; diphosphorus tetrahydride; octasulfur; chromic cyanide; sodium peroxide; aluminum nitride; permanganic acid

Hg₂CO₃, P₂H₄, S₈, Cr(CN)₃, Na₂O₂, AlN, HMnO₄

21.    Name the following:
HClO₂; Al₄C₃; NaIO₄; As₂O₃; NiSO₃; H₂Se
chlorous acid, aluminum carbide, sodium periodate, diarsenic trioxide, nickel sulfite, hydroselenic acid

22.    Calculate the atomic weight of silicon from the following isotopic masses and abundances:
²⁸Si (92.28%) 27.9866; ²⁹Si (4.67%) 28.9866, ³⁰Si (3.05%) 29.9832

27.9866(0.9228) + 28.9866(0.0467) + 29.9832(0.0305) = 28.09 (4 sigfigs)

23.    A 4.000-g sample of a phosphorus sulfide was burned in oxygen, and the products reacted with calcium hydroxide to form 17.819 g of a mixture of solid Ca₃(PO₄)₂ and CaSO₃. Addition of hydrochloric acid caused the calcium sulfite to dissolve leaving 11.273 g of calcium phosphate. Determine the empirical formula of the phosphorus sulfide.
Mass of calcium phosphate = 11.273 g = 11.273/(3(40)+2(31+64)) = 0.0364 mole
mass of calcium sulfite = 17.819-11.273 = 6.546 g = 6.546/(40+32+48) = 0.0546 mole
0.0364 mol calcium phosphate contain 2(0.0364) = 0.0728 mol P
0.0546 mol calcium sulfite contain 0.0546 mol S
Ratio: P: 0.0728/0.0546 = 1.333; S: 0.0546/0.0546 = 1.000
Empirical formula = P₄S₃

24.    (A) What is the mass of solute in 345 mL of 2.20 M NiCl₂?
0.345(2.20) mol NiCl₂ = 0.759 mol = 0.759(58.7+71) = 98.4 g

(B) A 50.0% solution of sulfuric acid (50 g H₂SO₄, 50 g water) has a density of 1.395 g/mL. What is the molarity of this solution?

One liter of solution weighs 1000(1.395) = 1395 g, and contains 0.50(1395) = 697.5 g = 697.5/(2+32+64) = 7.12 mol. Molarity = 7.12
(C) When sodium metal reacts with water, H₂ is evolved and a solution of NaOH is formed. What is the molarity of NaOH produced when 4.6 g Na metal is dissolved in water, and the final volume of the solution is made up to 500.0 mL?

Moles Na = moles NaOH = 4.6/23 = 0.20
0.20 moles in 0.5 liter = 0.40 moles in 1 liter
Answer = 0.40 M

25.    MnO₂ + 4HBr Br₂ + MnBr₂ + 2H₂O
How many millimoles of Br₂ are produced when 10.0 g MnO₂ are heated with 150 mL of 4.00 M HBr?

1 mol Br₂ from 1 mol MnO₂ and 4 mol HBr
10 g MnO₂ = 10.0/(55+32) = 0.115 mol
150 mL 4.00 M = 4(0.15) = 0.600 mol HBr
From equation 0.115 mol MnO₂ needs 4(0.115) = 0.460 mol HBr
Therefore MnO₂ is the limiting reagent, and 0.115 mol (115 mmol) Br₂ are formed.

26.    Calcium hypochlorite is a strong electrolyte but hypochlorous acid is a weak electrolyte. Write chemical equations that show what occurs when these two substances dissolve in water.
Ca(ClO)₂ + H₂O --> Ca²⁺(aq) + 2ClO(aq)

HClO + H₂O H⁺ (aq) + ClO(aq)