ANSWERS TO STUDY GUIDE FOR PLACEMENT EXAM
CHEM 101 or 105
PART 1. INTRODUCTORY CONCEPTS
Objective 1.
1. B Observation - one specific factual
2. D Law - a generic statement; a law is a statement that summarizes or describes pattern in numerous observations
3. A Hypothesis. An attempt to explain something is a hypothesis. A hypothesis is also called an "educated guess." For a guess to be "educated," it is based on prior knowledge of facts (which may need to be researched) or theories. A hypothesis based on a theory is a "theoretical explanation" but it is not a theory. A theory is a fundamental set of assumptions (or postulates) and rules that is used as a basis for formulating hypotheses (explaining things and making predictions).
Objective 2.
Classify the following descriptions of a sample of matter? A. solid, B. liquid, C. gas
1. B, liquid
2. A, solid
3. C, gas (molecules far apart)
Objective 3.
Which technique is being described? A. evaporation, B. filtration, C. distillation, D. chromatography
1. B filtration
2. C distillation
3. D chromatography
Objective 4.
1. A element
2. B compound
3. C mixture of compounds
Objective 5.
1. No, second letter must be lower case
2. No, fluorine is F, not Fl
3. Yes
Objective 6.
1-3. Metals are the left, nonmetals on the right and metalloids in between. 1. Si is a metalloid, 2. Na is a metal, 3. N is a nonmetal
4-6. Main groups are traditionally labelled IA, IIA. 4-5. K and N are main group elements 6. Mn is a transition element
7-9. IA - alkali metals IIA - alkaline earth metals, VIIA= halogens, VIIIA or 0 - noble gases
7. Li - alkali metal, 8. Ne - noble gas, 9. Cl - halogen
10-13 metals are better electrical and heat conductors, malleable (can be hammered into thin sheets like aluminum foil) and ductile (can be drawn out to a thin wire like copper) 10. B-Na, 11 A-Cu, 12 A-Al, 13. A-Ag
Objective 7.
1-3. In some color coded periodic tables, physical states of elements under ordinary conditions are coded as follows: red-gas, blue-liquid, black-solid.
1. B. mercury is a liquid (silvery liquid found in thermometers and blood pressure apparatus, 2. C - oxygen is gaseous (20% of the air we breath is made up of O2 molecules), 3. A - carbon is solid (as in coal, graphite (the "lead" in your pencil) anddiamond)
4. A, I2(s), 5. B, Br2(l), 6. D, Ne(g), 7. C, N2(g), 8. E, P4(s)
Objective 8.
1. B
Objective 9.
1. C. Solve: 3:8 as x:24, 3/8=x/24, x=9; or 24.0 g compound x (3.0 g "X" / 8.0 g compound)
2. A. same percentage. Law of definite composition is also known as law of constant composition.
Objective 10.
1. True. Electron mass is about 1/2000 of proton mass
2. False. Protons and neutrons are found in the nucleus. Electrons move around the nucleus
3. True. The nucleus is positively charged.
4. False. Electrons orbit around the nucleus; the neutrons are in the nucleus.
5. False -- it's much bigger, the typical radius of the atom (where the electrons roam about) is about 100,000x longer than the radius of the nucleus itself.
6. B: protons and neutrons have a mass of approx 1 amu each; electron mass is about 1/2000 of proton mass.
Objective 11.
1. C. Atomic number of Fe is 26; all Fe atoms have 26 protons. The superscript written next to Fe (56) is the mass number, which is equal to the number of protons AND neutrons. 26 protons + x neutrons = 56 nucleons. x=56-26 = 20 neutrons.
2. D. Atomic number of O is 8. All oxygen atoms have 8 protons. The symbol O-18 means an oxygen atom with 18 nucleons (protons and neutrons combined). 8 protons + 10 neutrons
Objective 12.
1. False. On average, at the same temperature, lighter molecules travel faster than heavier ones. This is the basis for separating uranium-235 and uranium-238.
2. False. Streams of heavier isotopes bend less. It's harder to push a football player vs. a small child.
Objective 13.
True or False
1. True --- they are all electrons
2. True
3. False --- most passed through with minor deflections; a few were deflected at large angles
4. True
5. True -- they were harder to detect because they are not charged
6. True
7. True
Objective 14.
1. D. a positive ion is formed by losing electrons
2. C a negative ion is formed by gaining electrons
Objective 15.
1. A. cations are positive ions, have more protons than electrons, charge = number of protons minus number of electrons
2. B. anions are negative ions
Objective 16.
1. B 13, 10. Atomic number of Al is 13; any atom or ion of aluminum has 13 protons. A +3 charge means 3 more protons than electrons. Charge = # protons - #electrons
2. A. 30, 32. one C has 6 protons, each O atom has 8 protons. 6+3(8) = 30 protons. A -2 charge means two electrons more than protons.
Objective 17.
1. A. group IA ions are always found in nature with a +1 charge.
2. C, group IIA ions are always found in nature with a +2 charge
3. D, group VIA ions are always found in nature with a -2 charge
Objective 18.
1. A, nonmetals tend to be involved in covalent bonding
2. A. nonmetals tend to be involved in covalent bonding or electron sharing
Objective 19.
1. A.
2. B
Objective 20.
1. D, 4
2. B. 42 electrons. Sulfite is SO32-; S has 16 protons, each O has 8. 16+3(8) = 40 protons. A -2 charge means two more electrons than protons.
Objective 21.
1. A, Names of oxoanions end in "ate" or "ite"
2. A. oxonanions are polyatomic ions of containing a nonmetal and one or more oxygen atoms
Objective 22.
1. B, trivial (either you know it or you don't)
2. B, trivial
Objective 23.
1. A, ionic. Metals such as Mg form ionic compounds
2. B. molecular. Compounds with no metal and no ammonium group are ionic
3. A. ionic. Ammonium compounds are ionic. The cation is ammonium (NH4+)
4. B. molecular. NH3 is ammonia, a molecular compound; do not confuse this with ammonium.
5. A. ionic. Ammonium compounds are ionic. The cation is ammonium (NH4+)
Objective 24.
1. B. The formula of a molecular compound tells you how many atoms of each kind are in one molecule
2. C. 3. Calcium ion is Ca2+, phosphate is PO43-. A formula unit for an ionic compound is defined as the simplest set of ions with a total charge of zero. In this case, it would be 3 cations and 2 anions. 3(+2) + 2(-3) =0
Objective 25.
1. A.
2. B. ionic compounds have high melting points
Objective 26.
1. B. Based on location in periodic table, Calcium ion is Ca2+, chloride is Cl-. The formula unit consists of one cation and two anions: 1x(+2) + 2x(-1) = 0.
2. B. NF3 is a molecular binary compound; use Greek prefix to indicate number of atoms of each element in one molecule; greek prefix for 3 is "tri"; do not use "mono"; change ending of second element to "ide"
3. B. Based on location in periodic table Co is a transition metal; its charge needs to be indicated using roman numeral in parentheses. Figure out cation charge is +2 based on chloride being Cl-
Objective 27.
1. C. Ammonium is NH4+ and phosphate is PO43-. One formula unit consists of 3 cations and one anion. 3x(+1) + 1(-3)=0.
2. B. Recognize carbonate as CO32-. and figure out that the charge of copper is +2. Indicate charge of copper in roman numeral in parentheses since it is a transition metal.
Objective 28. Read and write formulas of acids
1. C. ClO2- is chlorite, HClO2 is chlorous acid
2. A. The hydro prefix indicates that we're dealing with a non-oxoacid.
Objective 29. Classify changes as physical or chemical
1. B. Simple phase changes (melting, vaporization, sublimation, etc.) do not involve a change in composition.
2. A, Chemical changes involve a change in composiiton --- a rearrangement of atoms to form new formula units (molecules)
3. A, chemical property. A chemical property describes chemical changes that a substance undergoes.
Objective 30. Identify reactants and products of a chemical reaction
1.B. X, 5 g to be precise, was produced. If you have more of something after a reaction, it is a product of the reaction. If you have less of something after a reaction, it is a reactant.
2. C. N2 and H2 are the reactants, NH3 is a product
Objective 31. Construct a balanced chemical equation.
1. A. Do not change subscripts when balancing.
2. C.
3. C. Since C appears once on both sides (in C2H4 on the left and CO2 on the right) the coefficients of C2H4 and CO2 must be in a 1-to-2 ratio.
4. C. "aq" means aqueous (dissolved in water). CO2 should shown as CO2(g); bubbles are gaseous. Baking soda is a solid, so it should be written as NaHCO3(s)
Objective 32. Classify and predict products of simple reactions.
1. C. Displacement, or single replacement. Hydrogen is displaced by Magnesium.