[Onorato]

Hey guys, I just took a practice exam and have some questions.  It doesn't matter if you cannot answer all of them I have, by answering just one will help me a great deal!  Please respond, I thank you for your help and knowledge in my preparation for the NYS June 2007 Chemistry Regents Exam.  The questions I have are as follows:
(taken off a Regents exam, with the answer key, which is how I know the correct answers, just not why)

1. What is the total number of electrons shared in the bonds between the two carbon atoms in a molecule of
H-C(triple bond)C-H?
    I thought the answer was three, but it is in fact six.  Why?  Don't they share three electrons?


2. Which ion, when combined with chloride ions, Cl-, forms an insoluble substance in water?
            1 Fe+2                  3 Pb+2
            2 Mg+2                 4 Zn+2

    The correct answer is Pb with a charge of +2, but why?  They are all metals.


3. The compounds CH3OCH3 and CH3CH2OH are isomers of each other.  These two compounds must have the same

       1 density                  3 melting point
       2 reactivity               4 molecular formula

I chose density, considering they were laid out differently and have a different density, which was wrong.  The correct answer is molecular formula, while in the question it clearly shows them having different molecular formulas.  Clarification?


4. Given the balanced equation with an unknown compound represented by X:

                           enzyme
C6H12O6(aq) ------------> 2X + 2CO2(g)

    Which compound is represented by X?

1 CH3OH(aq)
2 CH2(OH)4(aq)
3 CH3CH2OH(aq)
4 CH2OHCH2OH(aq)

    I couldn't figure out this question.  I tried to find the difference between the carbon, hydrogen, and oxygen atoms on each side of the equation.  I came out with carbon being two, hydrogen being twelve, and oxygen being two.  That means the substance has to have those divided by two, because there is a two in front of the X.  None of these equations fit that, the correct answer is three.  ?

5. Given the table below shows students' examples of proposed models of the atom:

    Model      Location of Protons                                  Location of Electrons

       A              in the nucleus                                                 specific shells

       B              in the nucleus                                                  regions of most probable location

       C              dispersed throughought the atom               specific shells

       D               dispersed throughout the atom                  regions of most probable location



    Which model correctly describes the locations of protons and electrons in the wave-mechanical model of the atom?

1 A
2 B
3 C
4 D

          This one, I understand, may be difficult to answer because I think the wave-mechanical model seems too specific.  I chose A, because I know electrons are in orbitals, while the correct answer is B.  This may be just a definition question, but what does regions of most probable location mean?



    I thank you for reading this and helping me with my NYS State Exam/Regents.  It really means a lot to me, the exam is on June 20, 2007, thank you for responding in the limited amount of time.

[Borek]

1. What is the total number of electrons shared in the bonds between the two carbon atoms in a molecule of
H-C(triple bond)C-H?
    I thought the answer was three, but it is in fact six.  Why?  Don't they share three electrons?

Three electrons each.

2. Which ion, when combined with chloride ions, Cl-, forms an insoluble substance in water?
            1 Fe+2                  3 Pb+2
            2 Mg+2                 4 Zn+2

    The correct answer is Pb with a charge of +2, but why?  They are all metals.

Google salt solubility rules. That's a thing you will have to remember.

3. The compounds CH3OCH3 and CH3CH2OH are isomers of each other.  These two compounds must have the same

       1 density                  3 melting point
       2 reactivity               4 molecular formula

I chose density, considering they were laid out differently and have a different density, which was wrong.  The correct answer is molecular formula, while in the question it clearly shows them having different molecular formulas.  Clarification?

Check isomer definition. Both compounds have the same composition.

4. Given the balanced equation with an unknown compound represented by X:

                           enzyme
C6H12O6(aq) ------------> 2X + 2CO2(g)

    Which compound is represented by X?

1 CH3OH(aq)
2 CH2(OH)4(aq)
3 CH3CH2OH(aq)
4 CH2OHCH2OH(aq)

    I couldn't figure out this question.  I tried to find the difference between the carbon, hydrogen, and oxygen atoms on each side of the equation.  I came out with carbon being two, hydrogen being twelve, and oxygen being two.  That means the substance has to have those divided by two, because there is a two in front of the X.  None of these equations fit that, the correct answer is three.

Check your carbons.

Last one left for someone else, gotta go.

[Onorato]

Thank you so much for the explanations, they really helped.  I'm about to take the exam in an hour, thanks for clarifying the questions I had.