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Physical Setting / Chemistry - New York Regents January 2014 Exam

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Part A
Answer all questions in this part.
   Directions (1–30): For each statement or question, record on your separate answer sheet the number of the
word or expression that, of those given, best completes the statement or answers the question. Some questions
may require the use of the 2011 Edition Reference Tables for Physical Setting/Chemistry.

1.
1 What is the approximate mass of a proton?
  (1) 1 u                 (3) 1 g
  (2) 0.0005 u            (4) 0.0005 g
Answer: 1

2.
2 An electron in a sodium atom gains enough
  energy to move from the second shell to the
  third shell. The sodium atom becomes
  (1) a positive ion
  (2) a negative ion
  (3) an atom in an excited state
  (4) an atom in the ground state
Answer: 3

3.
3 Which particle has no charge?
  (1) electron            (3) positron
  (2) neutron             (4) proton
Answer: 2


4.
4 Which quantity represents the number of
  protons in an atom?
  (1) atomic number
  (2) oxidation number
  (3) number of neutrons
  (4) number of valence electrons
Answer: 1

5.
5 The element sulfur is classified as a
  (1) metal                (3) nonmetal
  (2) metalloid            (4) noble gas
Answer: 3

6.
6 The elements in Group 2 have similar chemical
  properties because each atom of these elements
  has the same
  (1) atomic number
  (2) mass number
  (3) number of electron shells
  (4) number of valence electrons
Answer: 4

7.
7 What is formed when two atoms of bromine
  bond together?
  (1) a monatomic molecule
  (2) a diatomic molecule
  (3) a heterogeneous mixture
  (4) a homogeneous mixture
Answer: 2

8.
8 Gold can be flattened into an extremely thin
  sheet. The malleability of gold is due to the
  (1) radioactive decay mode of the isotope Au-198
  (2) proton-to-neutron ratio in an atom of gold
  (3) nature of the bonds between gold atoms
  (4) reactivity of gold atoms
Answer: 3

9.
9 Which term represents the attraction one atom
  has for the electrons in a bond with another atom?
  (1) electronegativity
  (2) electrical conductivity
  (3) first ionization energy
  (4) mechanical energy
Answer: 1

10.
10 Salt water is classified as a
   (1) compound because the proportion of its
       atoms is fixed
   (2) compound because the proportion of its
       atoms can vary
   (3) mixture because the proportion of its
       components is fixed
   (4) mixture because the proportion of its
       components can vary
Answer: 4

11.
11 Which substance can not be broken down by a
   chemical change?
   (1) ammonia            (3) ethane
   (2) arsenic            (4) propanal
Answer: 2

12.
12 Some physical properties of two samples of iodine-127 
   at two different temperatures are shown in the table below.
                   Selected Physical Properties of Iodine-127 Samples at 1 atm
                           
               Sample       Sample Temperature(K)            Description         Density(g/cm3)
                                   
                  1                  298              dark-gray crystals             4.933
                  2                  525              dark-purple gas                0.006
               These two samples are two different
               (1) mixtures                                 (3) phases of matter
               (2) substances                               (4) isotopes of iodine
Answer: 3

13.
13 Powdered iron is magnetic, but powdered sulfur
   is not. What occurs when they form a mixture in a
   beaker at room temperature?
   (1) The iron retains its magnetic properties.
   (2) The iron loses its metallic properties.
   (3) The sulfur gains magnetic properties.
   (4) The sulfur gains metallic properties.
Answer: 1

14.
14 Which property is a measure of the average
   kinetic energy of the particles in a sample of
   matter?
   (1) mass                (3) pressure
   (2) density             (4) temperature
Answer: 4

15.
15 According to the kinetic molecular theory,
   which statement describes the particles of an
   ideal gas?
   (1) The gas particles are arranged in a regular
       pattern.
   (2) The force of attraction between the gas
       particles is strong.
   (3) The gas particles are hard spheres in
       continuous circular motion.
   (4) The collisions of the gas particles may result
       in the transfer of energy.
Answer: 4

16.
16 The concentration of a solution can be
   expressed in
   (1) milliliters per minute
   (2) parts per million
   (3) grams per kelvin
   (4) joules per gram
Answer: 2

17.
17 Two hydrogen atoms form a hydrogen molecule
   when
   (1) one atom loses a valence electron to the other
       atom
   (2) one atom shares four electrons with the other
       atom
   (3) the two atoms collide and both atoms gain
       energy
   (4) the two atoms collide with sufficient energy
       to form a bond
Answer: 4

18.
18 Which type of formula represents the simplest
   whole-number ratio of atoms of the elements in
   a compound?
   (1) molecular formula (3) empirical formula
   (2) condensed formula (4) structural formula
Answer: 3

19.
19 The coefficients in a balanced chemical equation
   represent
   (1) the mass ratios of the substances in the
       reaction
   (2) the mole ratios of the substances in the
       reaction
   (3) the total number of electrons in the reaction
   (4) the total number of elements in the reaction
Answer: 2

20.
20 Systems in nature tend to undergo changes
   toward
   (1) lower energy and higher entropy
   (2) lower energy and lower entropy
   (3) higher energy and higher entropy
   (4) higher energy and lower entropy
Answer: 1

21.
21 Which formula represents an organic compound?
   (1) CaH2                (3) H2O2
   (2) C4H8                (4) P2O5
Answer: 2

22.
22 Which class of organic compounds contains
   nitrogen?
   (1) aldehyde          (3) amine
   (2) alcohol           (4) ether
Answer: 3

23.
23 Which term identifies a type of organic reaction?
   (1) deposition            (3) esterification
   (2) distillation          (4) sublimation
Answer: 3

24.
24 Which compound is classified as a hydrocarbon?
   (1) butanal             (3) 2-butanol
   (2) butyne              (4) 2-butanone
Answer: 2

25.
25 In an oxidation-reduction reaction, the number
   of electrons lost is
   (1) equal to the number of electrons gained
   (2) equal to the number of protons gained
   (3) less than the number of electrons gained
   (4) less than the number of protons gained
Answer: 1

26.
26 Which substance is an electrolyte?
   (1) C6H12O6(s)          (3) NaOH(s)
   (2) C2H5OH(ℓ)          (4) H2(g)
Answer: 3

27.
27 Which energy conversion must occur in an
   operating electrolytic cell?
   (1) electrical energy to chemical energy
   (2) electrical energy to nuclear energy
   (3) chemical energy to electrical energy
   (4) chemical energy to nuclear energy
Answer: 1

28.
28 Which compound yields H+ ions as the only
   positive ions in an aqueous solution?
   (1) KOH                  (3) CH3OH
   (2) NaOH                 (4) CH3COOH
Answer: 4

29.
29 Which statement describes the relative masses
   of two different particles?
   (1) A neutron has less mass than a positron.
   (2) A beta particle has less mass than a neutron.
   (3) An alpha particle has less mass than a
       positron.
   (4) An alpha particle has less mass than a beta
       particle.
Answer: 2

30.
30 Which term represents a type of nuclear reaction?
   (1) condensation
   (2) vaporization
   (3) single replacement
   (4) natural transmutation
Answer: 4


Part B–1
Answer all questions in this part.
   Directions (31–50): For each statement or question, record on your separate answer sheet the number of the
word or expression that, of those given, best completes the statement or answers the question. Some questions
may require the use of the 2011 Edition Reference Tables for Physical Setting/Chemistry.

31.
31 Which ion has the smallest radius?
   (1) O2–                 (3) Se2–
   (2) S2–                 (4) Te2–
Answer: 1

32.
32 Equal amounts of ethanol and water are mixed
   at room temperature and at 101.3 kPa. Which
   process is used to separate ethanol from the
   mixture?
   (1) distillation        (3) filtration
   (2) reduction           (4) ionization
Answer: 1

33.
33 A sample of a substance has these characteristics:
   • melting point of 984 K
   • hard, brittle solid at room temperature
   • poor conductor of heat and electricity as a solid
   • good conductor of electricity as a liquid or in
     an aqueous solution
    This sample is classified as
    (1) a metallic element
    (2) a radioactive element
    (3) a molecular compound
    (4) an ionic compound
Answer: 4

34.
34 Given the balanced equation representing a
   reaction:
             N2 + energy → N + N
   Which statement describes this reaction?
   (1) Bonds are broken, and the reaction is
       endothermic.
   (2) Bonds are broken, and the reaction is
       exothermic.
   (3) Bonds are formed, and the reaction is
       endothermic.
   (4) Bonds are formed, and the reaction is
       exothermic.
Answer: 1

35.
35 When lithium reacts with bromine to form the
   compound LiBr, each lithium atom
   (1) gains one electron and becomes a negatively
       charged ion
   (2) gains three electrons and becomes a negatively
       charged ion
   (3) loses one electron and becomes a positively
       charged ion
   (4) loses three electrons and becomes a positively
       charged ion
Answer: 3

36.
36 A beaker with water and the surrounding air are
   all at 24°C. After ice cubes are placed in the
   water, heat is transferred from
   (1) the ice cubes to the air
   (2) the beaker to the air
   (3) the water to the ice cubes
   (4) the water to the beaker
Answer: 3

37.
37 A sample of chlorine gas is at 300. K and
   1.00 atmosphere. At which temperature and
   pressure would the sample behave more like an
   ideal gas?
   (1) 0 K and 1.00 atm
   (2) 150. K and 0.50 atm
   (3) 273 K and 1.00 atm
   (4) 600. K and 0.50 atm
Answer: 4

38.
38 When a sample of a gas is heated in a sealed, rigid
   container from 200. K to 400. K, the pressure
   exerted by the gas is
   (1) decreased by a factor of 2
   (2) increased by a factor of 2
   (3) decreased by a factor of 200.
   (4) increased by a factor of 200.
Answer: 2

39.
39 The bright-line spectra produced by four elements are represented in the diagram below.
                                     Bright-Line Spectra of Four Elements
                                                Wavelength (nm)
Which elements are present in this mixture?
(1) A and D                                (3) Z and D
(2) A and X                                (4) Z and X
Answer: 1

40.
40 The graph below represents the relationship between time and temperature as heat is added at a constant
   rate to a sample of a substance.
During interval AB, which energy change occurs for the particles in this sample?
(1) The potential energy of the particles increases.
(2) The potential energy of the particles decreases.
(3) The average kinetic energy of the particles increases.
(4) The average kinetic energy of the particles decreases.
Answer: 1

41.
41 Given the potential energy diagram for a
   reversible chemical reaction:
Each interval on the axis labeled “Potential
Energy (kJ/mol)” represents 10. kilojoules per
mole. What is the activation energy of the
forward reaction?
(1) 10. kJ/mol         (3) 40. kJ/mol
(2) 30. kJ/mol         (4) 60. kJ/mol
Answer: 3

42.
42 Which condensed structural formula represents
   an unsaturated compound?
   (1) CH3CHCHCH3         (3) CH3CH3
   (2) CH3CH2CH3          (4) CH4
Answer: 1

43.
43 Which element reacts spontaneously with
   1.0 M HCl(aq) at room temperature?
   (1) copper             (3) silver
   (2) gold               (4) zinc
Answer: 4

44.
44 Given the balanced ionic equation:
      3Pb2+(aq) + 2Cr(s) → 3Pb(s) + 2Cr3+(aq)
   What is the number of moles of electrons gained
   by 3.0 moles of lead ions?
   (1) 5.0 mol              (3) 3.0 mol
   (2) 2.0 mol              (4) 6.0 mol
Answer: 4

45.
45 What is the amount of heat energy released
   when 50.0 grams of water is cooled from 20.0°C
   to 10.0°C?
   (1) 5.00 × 102 J        (3) 1.67 × 105 J
   (2) 2.09 × 103 J        (4) 1.13 × 106 J
Answer: 2

46.
46 What occurs at one of the electrodes in both an
   electrolytic cell and a voltaic cell?
   (1) Oxidation occurs as electrons are gained at
       the cathode.
   (2) Oxidation occurs as electrons are lost at the
       anode.
   (3) Reduction occurs as electrons are gained at
       the anode.
   (4) Reduction occurs as electrons are lost at the
       cathode.
Answer: 2

47.
47 Given the balanced equation representing a
   reaction:
     H2O(ℓ) + HCl(g) → H3O+(aq) + Cl-(aq)
   According to one acid-base theory, the H2O(ℓ)
   molecules
   (1) accept H+ ions      (3) donate H+ ions
   (2) accept OH- ions     (4) donate OH- ions
Answer: 1

48.
48 When an atom of the unstable isotope Na-24
   decays, it becomes an atom of Mg-24 because
   the Na-24 atom spontaneously releases
   (1) an alpha particle   (3) a neutron
   (2) a beta particle     (4) a positron
Answer: 2

49.
49 Which balanced equation represents nuclear
   fusion?

Answer: 3

50.
50 Which reaction releases the greatest amount of
   energy per kilogram of reactants?
(2) 2C + H2 → C2H2
(3) C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(ℓ)
(4) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(ℓ)
Answer: 1


Part B–2
Answer all questions in this part.
   Directions (51–65): Record your answers in the spaces provided in your answer booklet. Some questions
may require the use of the 2011 Edition Reference Tables for Physical Setting/Chemistry.

51.
Base your answers to questions 51 through 54 on the information below and on your knowledge of chemistry.
          The diagram below represents three elements in Group 13 and three elements in
      Period 3 and their relative positions on the Periodic Table.
   Some elements in the solid phase exist in different forms that vary in their physical
properties. For example, at room temperature, red phosphorus has a density of 2.16 g/cm3
and white phosphorus has a density of 1.823 g/cm3.
51 Identify the element from the diagram that will react with chlorine to form a compound
   with the general formula XCl4. [1]
Answer: MODEL ANSWER GIVEN BELOW
51 [1] Allow 1 credit. Acceptable responses include, but are not limited to:
             Si
             silicon
             element 14


52.
52 Consider the Period 3 elements in the diagram in order of increasing atomic number.
   State the trend in electronegativity for these elements. [1]
Answer: MODEL ANSWER GIVEN BELOW
52 [1] Allow 1 credit. Acceptable responses include, but are not limited to:
             As atomic number increases, the electronegativity increases.
             Electronegativity increases.
             from lower to higher


53.
53 Compare the number of atoms per cubic centimeter in red phosphorus with the
   number of atoms per cubic centimeter in white phosphorus. [1]
Answer: MODEL ANSWER GIVEN BELOW
53 [1] Allow 1 credit. Acceptable responses include, but are not limited to:
             White phosphorus has fewer atoms per cm3.
             Red has more.
        Note: Do not allow credit for a response that only indicates the number of atoms per cm3 in red
              phosphorus is different from the number of atoms per cm3 in white phosphorus.


54.
54 Identify one element from the diagram that will combine with phosphorus in the same
   ratio of atoms as the ratio in aluminum phosphide. [1]
Answer: MODEL ANSWER GIVEN BELOW
54 [1] Allow 1 credit. Acceptable responses include, but are not limited to:
             Ga
             indium
             element 31
             element 49


55.
Base your answers to questions 55 through 57 on the information below and on your knowledge of chemistry.
         The compounds KNO3 and NaNO3 are soluble in water.
      55 Compare the entropy of 30. grams of solid KNO3 at 20.°C with the entropy of 30. grams
         of KNO3 dissolved in 100. grams of water at 20.°C. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             The entropy of KNO3(s) is less than the entropy of KNO3(aq).
             The KNO3(aq) is more disordered.
             The solution is more random than the solid.
        Note: Do not allow credit for a response that only indicates the entropies are different.


56.
56 Explain why the total thermal energy of a sample containing 22.2 grams of NaNO3
   dissolved in 200. grams of water at 20.°C is greater than the total thermal energy of a
   sample containing 11.1 grams of NaNO3 dissolved in 100. grams of water at 20.°C. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             Both samples are at 20.°C, but the larger sample has more matter.
             The larger sample has twice as many particles.
             The total thermal energy is directly proportional to the masses of the samples.


57.
57 Compare the boiling point of a NaNO3 solution at standard pressure to the boiling point
   of water at standard pressure. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             The boiling point of the NaNO3 solution is higher than the boiling point of water.
             lower for H2O


58.
Base your answers to questions 58 through 61 on the information below and on your knowledge of chemistry.
         Ethene and hydrogen can react at a faster rate in the presence of the catalyst platinum.
      The equation below represents a reaction between ethene and hydrogen.
58 Determine the molar mass of the product. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for 30 g/mol, 30. g/mol, or for any value from 30.06 g/mol to 30.1 g/mol, inclusive.


59.
59 State the number of electrons shared between the carbon atoms in one molecule of the
   reactant ethene. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for 4 or four.


60.
60 Explain, in terms of activation energy, why the catalyzed reaction occurs at a faster rate. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             The catalyzed reaction pathway has a lower activation energy than the original reaction.
             Less energy is needed.


61.
61 Explain why the reaction is classified as an addition reaction. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             Hydrogen atoms are added to the ethene molecule at the site of the carbon-carbon double bond
             to form a single molecule.
             Two reactants combine to form a single product.
             Two substances form one.
             Two hydrogen atoms are added at C=C.
             An unsaturated reactant becomes a saturated product.
             The reaction is a hydrogenation reaction, which is a type of addition reaction.


62.
Base your answers to questions 62 and 63 on the information below and on your knowledge of chemistry.
        In a titration, 50.0 milliliters of 0.026 M HCl(aq) is neutralized by 38.5 milliliters of
      KOH(aq).
      62 In the space in your answer booklet, show a numerical setup for calculating the molarity
         of the KOH(aq). [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             (0.026 M)(50.0 mL) = MB (38.5 mL)
             MB = (0.026)(50)/38.5


63.
63 Complete the equation in your answer booklet for the neutralization by writing the
   formula of the missing product. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             KCl
             ClK
             K+(aq) + Cl-(aq)
             K+ + Cl-


64.
Base your answers to questions 64 and 65 on the information below and on your knowledge of chemistry.
         Table sugar, sucrose, is a combination of two simple sugars, glucose and fructose. The
      formulas below represent these simple sugars.
64 Identify the functional group that appears more than once in the fructose molecule. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             –OH
             OH
             alcohol
             hydroxyl
             hydroxy group
        Note: Do not allow credit for hydroxide ion or hydroxyl radical or OH-.


65.
65 Explain, in terms of atoms and molecular structure, why glucose and fructose are
   isomers of each other. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             The number of each kind of atom is the same in both, but their structures are not the same.
             Their molecular formulas are the same, but their structural arrangement of atoms is different.
             same molecular formula but different structural formulas
             The only difference is the arrangement of the atoms.



Part C
Answer all questions in this part.
   Directions (66–85): Record your answers in the spaces provided in your answer booklet. Some questions
may require the use of the 2011 Edition Reference Tables for Physical Setting/Chemistry.

66.
Base your answers to questions 66 through 70 on the information below and on your knowledge of chemistry.
          Baking soda, NaHCO3, can be commercially produced during a series of chemical
      reactions called the Solvay process. In this process, NH3(aq), NaCl(aq), and other chemicals
      are used to produce NaHCO3(s) and NH4Cl(aq).
          To reduce production costs, NH3(aq) is recovered from NH4Cl(aq) through a different
      series of reactions. This series of reactions can be summarized by the overall reaction
      represented by the unbalanced equation below.
                      NH4Cl(aq) + CaO(s) → NH3(aq) + H2O(ℓ) + CaCl2(aq)
      66 Write a chemical name for baking soda. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             sodium hydrogen carbonate
             sodium bicarbonate
             sodium acid carbonate
             monosodium carbonate
             bicarbonate of soda


67.
67 Determine the percent composition by mass of carbon in baking soda (gram-formula
   mass = 84 grams per mole). [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for 14% or for any value from 14.28% to 14.3%, inclusive.


68.
68 State the color of bromcresol green in a sample of NH3(aq). [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for blue.


69.
69 Determine the mass of NH4Cl that must be dissolved in 100. grams of H2O to produce
   a saturated solution at 70.°C. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for any value from 61 g to 63 g, inclusive.


70.
70 Balance the equation in your answer booklet for the overall reaction used to recover
   NH3(aq), using the smallest whole-number coefficients. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for     2 NH4Cl +  __ CaO →   2 NH3 + __ H2O + __ CaCl2.
        Note: Allow credit even if the coefficient “1” is written in front of CaO, H2O, and/or CaCl2.


71.
Base your answers to questions 71 through 75 on the information below and on your knowledge of chemistry.
          Rubbing alcohol is a product available at most pharmacies and supermarkets. One
      rubbing alcohol solution contains 2-propanol and water. The boiling point of 2-propanol is
      82.3°C at standard pressure.
      71 Explain, in terms of electronegativity differences, why a C—O bond is more polar than
         a C—H bond. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             There is a greater electronegativity difference in a C–O bond than in a C–H bond.
             The C–O bond is more polar because the electronegativity difference for a C–O bond is 0.8, and
             the electronegativity difference for a C–H bond is 0.4.
             The C–H bond has a smaller difference.
             The C–O is .8 and the C–H is .4.


72.
72 Identify a strong intermolecular force of attraction between an alcohol molecule and a
   water molecule in the solution. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             hydrogen bonding
             dipole–dipole


73.
73 Determine the vapor pressure of water at a temperature equal to the boiling point of
   the 2-propanol. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for any value from 48 kPa to 52 kPa, inclusive.


74.
74 Explain, in terms of charge distribution, why a molecule of the 2-propanol is a polar
   molecule. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             A 2-propanol molecule is polar because it has an asymmetrical distribution of charge.
             The charge distribution is uneven.
             The center of positive charge and the center of negative charge do not coincide.


75.
75 In the space in your answer booklet, draw a structural formula for the 2-propanol. [1]
Answer: MODEL ANSWER GIVEN BELOW
75 [1] Allow 1 credit.
        Examples of 1-credit responses:


76.
Base your answers to questions 76 and 77 on the information below and on your knowledge of chemistry.
          Silver-plated utensils were popular before stainless steel became widely used to make
      eating utensils. Silver tarnishes when it comes in contact with hydrogen sulfide, H2S, which
      is found in the air and in some foods. However, stainless steel does not tarnish when it
      comes in contact with hydrogen sulfide.
      76 In the space in your answer booklet, draw a Lewis electron-dot diagram for
         the compound that tarnishes silver. [1]
Answer: MODEL ANSWER GIVEN BELOW
76 [1] Allow 1 credit. The position of electrons may vary.
        Examples of 1-credit responses:


77.
77 In the ground state, an atom of which noble gas has the same electron configuration as
   the sulfide ion in Ag2S? [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             Ar
             argon
             element 18


78.
Base your answers to questions 78 through 81 on the information below and on your knowledge of chemistry.
          Common household bleach is an aqueous solution containing hypochlorite ions. A
      closed container of bleach is an equilibrium system represented by the equation below.
                       Cl2(g) + 2OH-(aq) ⇌ ClO-(aq) + Cl-(aq) + H2O(ℓ)
      78 Compare the rate of the forward reaction to the rate of the reverse reaction for this
         system. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             The rate of the forward reaction is equal to the rate of the reverse reaction.
             They are the same.
             equal


79.
79 State the change in oxidation number for chlorine when the Cl2(g) changes to Cl-(aq)
   during the forward reaction. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             0 to -1
             0 to 1-
             zero to negative one
             0 to minus one


80.
80 Explain why the container must be closed to maintain equilibrium. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             The container must be closed so that no matter can enter or leave, thus disturbing the
             equilibrium.
             If the container is open, Cl2 gas escapes.
             to keep the concentrations of the reactants and products constant


81.
81 State the effect on the concentration of the ClO- ion when there is a decrease in the
   concentration of the OH- ion. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
             The concentration of the ClO- ion decreases.
             [ClO-] decreases.
             lower ClO- concentration
             less ClO-


82.
Base your answers to questions 82 through 85 on the information below and on your knowledge of chemistry.
          Iodine has many isotopes, but only iodine-127 is stable and is found in nature. One
      radioactive iodine isotope, I-108, decays by alpha particle emission. Iodine-131 is also
      radioactive and has many important medical uses.
      82 Determine the number of neutrons in an atom of I-127. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for 74.


83.
83 Explain, in terms of protons and neutrons, why I-127 and I-131 are different isotopes
   of iodine. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
              I-127 atoms and I-131 atoms have the same number of protons, but different numbers of
              neutrons.
              Both have 53 p, but I-127 has 74 n while I-131 has 78 n.
              They have the same atomic number but different mass numbers.
              same atomic number but different numbers of neutrons
              The only difference is the number of neutrons.


84.
84 Complete the equation in your answer booklet for the nuclear decay of I-108. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit. Acceptable responses include, but are not limited to:
              104Sb
               51
              104Sb
              Sb-104
              antimony-104


85.
85 Determine the total time required for an 80.0-gram sample of I-131 to decay until only
   1.25 grams of the sample remains unchanged. [1]
Answer: MODEL ANSWER GIVEN BELOW
 Allow 1 credit for 48 d, 48.0 d, 48.1 d, or for any value from 48.12 d to 48.13 d, inclusive.



  Try the Quiz :     Physical Setting / Chemistry - New York Regents January 2014 Exam


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