January 2012 Chemistry Regents #3140
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Questions 
Answer  Link  Explanations 
31 What is the total number of valence electrons in a germanium atom in the ground state? (1) 22 (3) 32 (2) 2 (4) 4 
4 

2818 4 < last number of the electron configuration on the Periodic table 
32 Which element is paired with an excitedstate electron configuration for an atom of the element? (1) Ca: 2882 (2) Na: 282 (3) K: 2683 (4) F: 28 
3  link  excited states have an electron that has jumped up
K should be 2881 (ground state)

33 Given the balanced equations representing two chemical reactions: Cl_{2} + 2NaBr > 2NaCl + Br_{2} 2NaCl> 2Na + Cl_{2} Which types of chemical reactions are represented by these equations? (1) single replacement and decomposition (2) single replacement and double replacement (3) synthesis and decomposition (4) synthesis and double replacement 
1  link  see link

34 An ion that consists of 7 protons, 6 neutrons, and 10 electrons has a net charge of (I ) 4 (3) 3+ (2) 3 (4) 4+ 
3  link  the charge is the difference between the positive protons
and negative electrons

35 Which Lewis electrondot diagram represents a molecule having a nonpolar covalent bond?

1  link 
2 of the same element bonded= nonpolar bond 
36 Which quantity is equal to 50 kilojoules? (I ) 0.05J (3) 5 x 10^{3}J (2) 500J (4) 5 x 10^{4}J 
4  first replace kilo with x 10^{3} (table C
prefixes) 50 x 10^{3} which is 5 x 10^{4} 

37 Which compound is formed from its elements by an exothermic reaction at 298 K and 101.3 kPa? (1) C_{2}H_{4}(g) (2) HI(g) (3) H_{2}O(g) (4) NO_{2}(g) 
3  link  Table I exothermic has a negative delta H

38 At which temperature is the vapor pressure of ethanol equal to 80. kPa? (1) 48°C (3) 80. °C (2) 73°C (4) 101 °C 
2 
link

Table H 
39 At 25°C, gas in a rigid cylinder with a movable piston has a volume of 145 mL and a pressure of 125 kPa. Then the gas is compressed to a volume of 80. mL. What is the new pressure of the gas if the temperature is held at 25°C? (1) 69 kPa (3) 160 kPa (2) 93 kPa (4) 230 kPa 
4 
link

PV=PV (temperature is constant, so leave it out) 145ml x 125kPa= P x 80.ml 226 kPa=P 230kPa=P (sig figs) 
40 A 2400.gram sample of an aqueous solution contains 0.012 gram of NH_{3}. What is the concentration of NH3 in the solution, expressed as parts per million? (1) 5.0 ppm (2) 15 ppm (3) 20. ppm (4) 50. ppm 
1  link  (0.012g/2400.g) x 1,000,000=5.0ppm 