August 2007 Chemistry Regents #41-50

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Answer Explanations
1 count the bonds

2 electrons per bond

42 Given the balanced equation representing the reaction occurring in a voltaic cell:
Zn(s) + Pb2+(aq)==> Zn2+(aq) + Pb(s)
In the completed external circuit, the electrons flow from
(1) Pb(s) to Zn(s)
(2) Pb2+(aq) to Zn2+(aq)
(3) Zn(s) to Pb(s)
(4) Zn2+(aq) to Pb2+(aq)
3 solid metal to solid metal

lose to gain

ox to reduction

charge goes up to charge goes down

43 Which balanced equation represents a redox
reaction?
(1) CuCO3(s) ==> CuO(s) + CO2(g)
(2) 2KClO3(s)==>2KCl(s) + 3O2(g)
(3) AgNO3(aq) + KCl(aq) ==>AgCl(s) + KNO3(aq)
(4) H2SO4(aq) + 2KOH(aq)==> K2SO4(aq) + 2H2O(l)
2 look for the free element  O2
44 Given the unbalanced ionic equation:
3Mg + ____ Fe3+ ==> 3Mg2+ + ____ Fe
When this equation is balanced, both Fe3+ and Fe have a coefficient of
(1) 1, because a total of 6 electrons is transferred
(2) 2, because a total of 6 electrons is transferred
(3) 1, because a total of 3 electrons is transferred
(4) 2, because a total of 3 electrons is transferred
2 6+ on the right side so 6+ on the left

6 electrons transfer

45 A student collects the materials and equipment below to construct a voltaic cell.
two 250-mL beakers
wire and a switch
one strip of magnesium
one strip of copper
125 mL of 0.20 M Mg(NO3)2(aq)
125 mL of 0.20 M Cu(NO3)2(aq)
Which additional item is required for the construction of the voltaic cell?
(1) an anode (3) a cathode
(2) a battery (4) a salt bridge
4 voltaic needs a salt bridge
46 Given the balanced equation representing a reaction:
Zn(s) + 2HCl(aq)==>H2(g) + ZnCl2(aq)
Which set of reaction conditions produces H2(g) at the fastest rate?
(1) a 1.0-g lump of Zn(s) in 50. mL of 0.5 M HCl(aq) at 20.oC
(2) a 1.0-g lump of Zn(s) in 50. mL of 0.5 M HCl(aq) at 30.oC
(3) 1.0 g of powdered Zn(s) in 50. mL of 1.0 M HCl(aq) at 20.oC
(4) 1.0 g of powdered Zn(s) in 50. mL of 1.0 M HCl(aq) at 30.oC
4 high concentration and high surface area
2 table M
48 What is the pH of a solution that has a hydronium ion concentration 100 times greater than a solution with a pH of 4?
(1) 5       (3) 3
(2) 2        (4) 6
2 100 has 2 zeros pH has changed by 2

more hydronium more acidic pH decreases

4 one reactant-->natural

more than one artificial

 

50 A nuclear fission reaction and a nuclear fusion reaction are similar because both reactions
(1) form heavy nuclides from light nuclides
(2) form light nuclides from heavy nuclides
(3) release a large amount of energy
(4) absorb a large amount of energy
3 nuclear reactions release large amounts of energy

E=mc2

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