2.1 the First Sample Has a Ratio Of

Chapter 2

Practice Exercises

2.1 The first sample has a ratio of

Therefore, the second sample must have the same ratio of Cd to S:

Cross-multiplication gives,

(1.25 g Cd)(3.50 g S) = x(0.357 g S)

x = 12.3 g Cd

2.2 Compare the ratios of the mass of the compound before heating and the mass of the iron after heating, if they are the same, the compounds are the same.

Sample / Ratio
A / = 1.574
B / = 1.86
C / = 1.86
D / = 1.57

Compounds A and D are the same, as are compounds B and C.

2.3

The bottom number is the atomic number, found on the periodic table (number of protons). The top number is the mass number (sum of the number of protons and the number of neutrons). Since it is a neutral atom, it has 94 electrons.

2.4 contains 17 protons, 17 electrons, and 18 neutrons.

2.5 We can discard the 17 since the 17 tells the number of protons which is information that the symbol "Cl" also provides. In addition, the number of protons equals the number of electrons in a neutral atom, so the symbol "Cl" also indicates the number of electrons. The 35 is necessary to state which isotope of chlorine is in question and therefore the number of neutrons in the atom.

2.6 2.24845 × 12 u = 26.9814 u

2.7 Copper is 63.546 u ¸12 u = 5.2955 times as heavy as carbon

2.8 (0.198 × 10.0129 u) + (0.802 × 11.0093 u) = 10.8 u

2.9 (a) 1 Ni, 2 Cl

(b) 1 Fe, 1 S, 4 O

(d) 1 Co, 2 N, 12 O, 12 H

2.10 (a) 2 N nitrogen, 4 H hydrogen, 3 O oxygen

(b) 1 Fe iron, 1 N nitrogen, 4 H hydrogen, 2 S sulfur, 8 O oxygen

(d) 6 C carbon, 4 H hydrogen, 1 Cl chlorine, 1 N nitrogen, 2 O oxygen

2.11 This is a balanced chemical equation, and the number of each atom that appears on the left is the same as that on the right: 1 Mg, 2 O, 4 H, and 2 Cl.

2.12 Mg(OH)2(s) + 2HCl(aq) g MgCl2(aq) + 2H2O

2.13 6 N, 42 H, 2 P, 20 O, 3 Ba, and 12 C are on both the products and the reactants sides of the equation, therefore the reaction is balanced.

2.14 The term "octa' means eight, therefore there are 8 carbon atoms in octane. The formula for an alkane is CnH2n+2, so octane has 8 carbons and ((2 × 8) + 2) = 18 H. The condensed formula is CH3CH2CH2CH2CH2CH2CH2CH3, and the structural format is:

2.15 The condensed formula is CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

The structural formula is:

2.16 (a) Propanol: CH3CH2CH2OH

(b) Butanol: CH3CH2CH2CH2OH

2.17 (a) Fe: 26 protons and 26 electrons

(b) Fe3+: 26 protons and 23 electrons

(d) N: 7 protons and 7 electrons

2.18 (a) O: 8 protons and 8 electrons

(b) O2–: 8 protons and 10 electrons

(d) Al: 13 protons and 13 electrons

2.19 (a) NaF (b) Na2O (c) MgF2 (d) Al4C3

2.20 (a) Ca3N2 (b) AlBr3 (c) Na3P d) CsCl

2.21 (a) CrCl3 and CrCl2, Cr2O3 and CrO

(b) CuCl, CuCl2, Cu2O and CuO

2.22 (a) Au2S and Au2S3, Au3N and AuN

(b) SnS and SnS2, Sn3N2 and Sn3N4

2.23 (a) KC2H3O2 (b) Sr(NO3)2 (c) Fe(C2H3O2)3

2.24 (a) Na2CO3 (b) (NH4)2SO4

2.25 (a) phosphorous trichloride

(b) sulfur dioxide

2.26 (a) AsCl5 (b) SCl6 (c) S2Cl2

2.27 (a) K2O (b) BaBr2 (c) Na3N (d) Al2S3

2.28 (a) aluminum chloride (b) barium sulfide

2.29 (a) postassium sulfide (b) magnesium phosphide

2.30 (a) Al2S3 (b) SrF2 (c) TiO2 d) Au2O3

2.31 (a) lithium carbonate

(b) iron(III) hydroxide

2.32 (a) KClO3 (b) Ni3(PO4)2

2.33 diiodine pentaoxide

2.34 chromium(III) acetate

Review Questions

2.1 The first law of chemical combination is the law of conservation of mass: no detectable gain or loss of mass occurs in chemical reactions. The other law is the law of definite proportions: in a given chemical compound, the elements are always combined in the same proportions by mass.

2.2 Isotopes of a particular element have nearly identical chemical properties and the average mass of an atom is independent, almost, of the source of the atom.

2.3 Conservation of mass derives from the postulate that atoms are not destroyed in normal chemical reactions. The Law of Definite Proportions derives from the notion that compound substances are always composed of the same types and numbers of atoms of the various elements in the compound.

2.4 This is the Law of Definite Proportions, which guarantees that a single pure substance is always composed of the same ratio of masses of the elements that compose it.

2.5 (a) To test the law of conservation of mass, a reaction would have to be carried out in which the mass of the reactants and the mass of the products are weighed and shown to be the same.

(b) The law of definite proportions could be shown by demonstrating that no matter how a compound is made, the same proportions by mass are used. This could be done by decomposing a compound and showing that the masses of the elements are always in the same ratio.

c) To test the law of multiple proportions, two different compounds made up of the same elements would have to be decomposed. The amount used would have to keep mass of one of the elements constant, and then the masses of other the element from the different samples would have to be in a ratio of small whole numbers.

2.6 Protons, , +1 charge

Electron, , –1 charge

Neutron, , no charge

2.7 Nearly all of the mass is located in the nucleus, because this is the portion of the atom where the proton and the neutron are located.

2.8 A nucleon is a subatomic particle found in the atomic nucleus. We have studied neutrons and protons.

2.9 The atomic number is equal to the number of protons in the nucleus of the atom, and the mass number is the sum of the number of neutrons and the number of protons. The atomic number (symbol Z) is designated by a subscript preceding the chemical symbol and the mass number (symbol A) is a superscript preceding the chemical symbol.

2.10 (a) mass number (b) atomic number

2.11 (a) (b) (c) (d)

2.12 For all group IA elements (the alkali metals), the formula is MX, that is one Cl per atom of metal. For all group IIA elements (the alkaline earth metals), the formula is MX2, that is two Cl atoms per atom of metal. The correspondence in formula and the similarities in chemical behavior allowed Mendeleev to locate theses two series into their separate groups on the periodic table.

2.13 Mendeleev constructed his periodic table by arranging the elements in order of increasing atomic weight, and grouping the elements by their recurring properties. The modern periodic table is arranged in order of increasing number of protons.

2.14 Strontium and calcium are in the same Group of the periodic table, so they are expected to have similar chemical properties. Strontium should therefore form compounds that are similar to those of calcium, including the sorts of compounds found in bone.

2.15 Silver and gold are in the same periodic table group as copper, so they might well be expected to occur together in nature, because of their similar properties and tendencies to form similar compounds.

2.16 Cadmium is in the same periodic table group as zinc, but silver is not. Therefore cadmium would be expected to have properties similar to those of zinc, whereas silver would not.

2.17 The superscript before the symbol indicates the mass number; the superscript after the symbol indicates the charge on the atom; the subscript before the symbol indicates the atomic number; and the subscript after the symbol indicates the number of atoms in the compound.

For example:

Nitrogen has 7 protons and 7 electrons for a neutral atom. The molecule has two atoms in it, and the isotope with 7 neutrons gives it a mass number of 14

2.18 See Figure in the margin of page 50.

2.19 (a) Li

(b) I

(d) Xe

(e) Sm

(f) Pu

(g) Mg

2.20 Luster, electrical conductivity, thermal conductivity, ductility, and malleability are the characteristic properties of metals.

2.21 Mercury is used in thermometers because it is a liquid, and tungsten is used in light bulbs because is has such a high melting point.

2.22 The noble gases: He, Ne, Ar, Kr, Xe, and Rn

2.23 Mercury and bromine

2.24 They are semiconductors.

2.25 See figure 2.7

2.26 The heavy line separates the metals from the nonmetals, and the metalloids border the line.

2.27 Metals which are used to make jewelry are those that do not corrode, silver, gold, and platinum. Iron would be useless for jewelry because it is susceptible to rusting. Potassium reacts violently with water to form hydrogen and potassium hydroxide.

2.28 Luster, malleability, color, and brittleness are some trends that are mentioned in terms of moving from the metals to the nonmetals across the periodic table, or moving down a group from nonmetals to metals.

2.29 (a) In general, melting points decrease from left to right across the periodic table and increases from top to bottom.

(b) In general, boiling points decrease from left to right across the periodic table and increases from top to bottom.

(c) In general, density has a maximum in the middle of the periodic table and falls off to the right and left. Also, the density increases moving down a group.

2.30 This may stand for the name of an element or for the name of one atom of an element.

2.31 The smallest particle that is representative of a particular element is the atom of that element. A molecule is a representative unit that is made up of two or more atoms linked together.

2.32 H2, hydrogen N2, nitrogen, O2, oxygen F2, fluorine

Cl2, chlorine Br2. bromine I2, iodine

2.33 A chemical reaction is balanced when there is the same number of each kind of atom on both the reactant and product side of the equation; and the total charges on both the reactant and product sides of the equation are the same. These conditions must be met due to the law of conservation of matter.

2.34 Reactants are the substances to the left of the arrow in a reaction that are present before the reaction begins. Products are the substances to the right of the arrow in a reaction and they are formed during the reaction and are present when the reaction is over.

2.35 (a) Magnesium reacts with oxygen to give (yield) magnesium oxide.

(b) The reactants are Mg and O2.

(d) 2Mg(s) + O2(g) ® 2MgO(s)

2.36 2C8H18(l) + 25O2(g) ® 18CO2(g) + 18H2O

2.37 The noble gases: He, Ne, Ar, Kr, Xe, and Rn

2.38 S8, P4

2.39 Nonmetals

2.40 (a) CH4 (b) NH3 (c) TeH2 (d) HI

2.41 PH3

2.42 HAt

2.43 SnH4

2.44 (a) CH4, component of natural gas (b) CH3CH3, component of natural gas

2.45 (a) CH3OH (b) CH3CH2OH

2.46 C10H22 or CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

2.47 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3

or CH3(CH2)21CH3 or C23H48

2.48 All of the elements are nonmetals, and the formula is not in the smallest whole number ratio.

2.49 methane:

ethane:

propane:

butane:

methanol:

ethanol:

decane (10 carbons):

23 carbon hydrocarbon

2.50 (a) An ionic compound is formed by the transfer of electrons, and it is accompanied by the formation of ions of opposite charge.

(b) Molecular compounds arise from the sharing of electrons between atoms, rather than from the complete transfer of electrons as in (a).

2.51 Metals react with nonmetals.

2.52 Nonmetals react with metals, nonmetals, and metalloids.

2.53 Nonmetals are more frequently found in compounds because of the large variety of ways they may combine. A particularly illustrative example is the combination of carbon, a nonmetal, with other elements. So many compounds are possible that there is one entire area of chemistry devoted to the study of carbon compounds, organic chemistry.

2.54 An ion is a charged particle. It can be monatomic or polyatomic, and it can have either a positive or a negative charge. It is derived from an atom or a molecule by gain or loss of electrons. Atoms and molecules are neutral.

2.55 In ionic substances, no molecules exist. Rather we have a continuous array of cations and anions, which are present in a constant ratio. The ratio is given by the formula unit.

2.56 Al2Cl6 is molecular because the smallest whole number ratio of elements is not used in the formula.

2.57 (a) Na, Na+

(b) These particles have the same number of nueclei.

(d) These particles could have different numbers of neutrons, if they are different isotopes.

(e) These particles do not have the same number of electrons; Na+ has one less electron.

2.58 A cation is a positively charged ion with one or fewer electrons than its neutral atom. An anion is a negatively charged ion with one or more electrons than its neutral atom. A polyatomic ion is made up of more than one atom; the whole unit is the ion.

2.59 Titanium lost four electrons to form Ti4+; it has 22 protons and 18 electrons.

2.60 Negative

2.61 Nitrogen gained 3 electrons to form N3–; it has 7 protons and 10 electrons.

2.62 Rb forms a +1 cation (Rb+) and Cl forms a –1 anion (Cl–), so the formula should be RbCl. The cation is first in the formula, therefore the formula should be Na2S.

2.63 The formula should have the smallest whole numbers possible. The formula should be TiO2.

2.64 (a) Fe2+, Fe3+