June 2008 Chemistry Regents #31-40

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Questions 1-10 Questions 11-20 Questions 21-30 Questions 31-40 Questions 41-50

 

Questions

AnswerExplanations
31 The wave-mechanical model of the atom is required to explain the
(1) mass number and atomic number of an atom
(2) organization of atoms in a crystal
(3) radioactive nature of some atoms
(4) spectra of elements with multielectron atoms		4wave-mechanical model ==>probable electron location

electrons==> spectra

32 Magnesium and calcium have similar chemical properties because an atom of each element has the same total number of
(1) electron shells             (3) neutrons
(2) valence electrons        (4) protons		2same group same valence electrons
2atomic number = # protons

mass number= protons + neutrons

34 A barium atom attains a stable electron configuration when it bonds with
(1) one chlorine atom
(2) two chlorine atoms
(3) one sodium atom
(4) two sodium atoms		2Ba2+ needs 2 Cl-
35 A student measures the mass and volume of a piece of aluminum. The measurements are 25.6 grams and 9.1 cubic centimeters. The student calculates the density of the aluminum. What is the percent error of the student’s calculated density of aluminum?
(1) 1%      (3) 3%
(2) 2%      (4) 4%		425.6g/9.1cm3 =2.81

use Table S for actual density 2.698

(2.81*2.698/2.698) * 100%

36 Given the balanced equation representing a reaction:
2H2 + O2  ==>2H2O
What is the total mass of water formed when 8 grams of hydrogen reacts completely with 64 grams of oxygen?
(1) 18 g      (3) 56 g
(2) 36 g      (4) 72 g		4conservation of mass

if 8g reacts completely with 64g you get 72 grams produced

37 Which compound contains both ionic and  covalent bonds?
(1) ammonia
(2) methane
(3) sodium nitrate
(4) potassium chloride		3Write the formula

NaNO3

3 different elements and 1 is a metal

38 An iron bar at 325 K is placed in a sample of water. The iron bar gains energy from the water if the temperature of the water is
(1) 65 K     (3) 65°C
(2) 45 K     (4) 45°C		3higher than 325K

convert to K by adding 273 to C

3they have to be bonded and all are the same structure
40 Given the balanced equation representing a reaction:
Cu + S==> CuS + energy
Which statement explains why the energy term is written to the right of the arrow?
(1) The compound CuS is composed of two metals.
(2) The compound CuS is composed of two nonmetals.
(3) Energy is absorbed as the bonds in CuS form.
(4) Energy is released as the bonds in CuS form.		4see answer

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