[Michael L.]

Hey everybody,

I've taken quite a few practice tests, and there are some questions I'm not sure how to solve.  Could somebody please help me out?

June 2006 #19

19 Which balanced equation represents an
endothermic reaction?
(1) C(s) + O2(g) → CO2(g)
(2) CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
(3) N2(g) + 3H2(g) → 2NH3(g)
(4) N2(g) + O2(g) → 2NO(g)

January 2007 #13, 20, 29

13 Which substance, when dissolved in water,
forms a solution that conducts an electric current?
(1) C2H5OH (3) C12H22O11
(2) C6H12O6 (4) CH3COOH

20 In which reaction are electrons transferred from
one reactant to another reactant?
(1) 2Ca(s) + O2(g) → 2CaO(s)
(2) AgNO3(aq) + KCl(aq) →
AgCl(s) + KNO3(aq)
(3) HCl(aq) + NaOH(aq) →
NaCl(aq) + H2O( )
(4) H3O+(aq) + OH–(aq) → 2H2O(l)

29 Which compound has hydrogen bonding
between its molecules?
(1) CH4 (3) KH
(2) CaH2 (4) NH3

June 2007 #23, 46

23 Which balanced equation represents an
oxidation-reduction reaction?
(1) BaCl2 + Na2SO4→BaSO4 + 2NaCl
(2) C+H2O →CO + H2
(3) CaCO3 →CaO + CO2
(4) Mg(OH)2 + 2HNO3 →Mg(NO3)2 + 2H2O

46 The organic compound represented by the
condensed structural formula CH3CH2CH2CHO
is classified as an
(1) alcohol (3) ester
(2) aldehyde (4) ether

August 2007 # 43

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)

Thanks in advance!

[Borek]

Please read forum rules. You are expected to try first, ask questions later.

[Michael L.]

I've completed every other multiple choice question in the mentioned Regents tests; those were the only ones I've had trouble with.  I've tried to do them, but I'm not sure what I'm doing wrong.

For #19, I'm not sure how to solve this because I would think energy would be part of the equation.
For # 13, would an ionic substance be the answer?  How can you identify one?
For #20, I'm not even sure how to start this one.
For #29, I don't understand how to recognize hydrogen bonding; could somebody explain it to me?
For #23, I'm not sure what to do.
For #46, how can I distinguish between the organic compounds? 
For #43, isn't water formed in a redox reaction?  The answer is not choice 4, though.

Thanks in advance for any help.

[Ak]

for the oxidation and reduction questions u need to work it out by giving every element a degree of oxidation..

ex.

1) Ba(+2)Cl(-1x2) + Na(+1x2)S(+6)O(-2x4)-->Ba(+2)S(+6)O(-2x4) + Na(+1)Cl(-1)
(2) C+H2O →CO + H2
(3) CaCO3 →CaO + CO2
(4) Mg(OH)2 + 2HNO3 →Mg(NO3)2 + 2H2O

in 1) There is no change in the oxidation state of any element...therefore there is no oxidation-reduction rxn...and btw elements that are by themselves such as C or H2 have an oxidation state of O

[Michael L.]

Thanks, that helps.  How did you know which oxidation state to use for each element, if several are listed in the periodic table?

[Borek]

How did you know which oxidation state to use for each element

http://www.chembuddy.com/?left=balancing-stoichiometry&right=oxidation-numbers-method

19 Which balanced equation represents an endothermic reaction?
(1) C(s) + O2(g) → CO2(g)
(2) CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
(3) N2(g) + 3H2(g) → 2NH3(g)
(4) N2(g) + O2(g) → 2NO(g)

I suppose they mean combustion is "always" exothermic. Which is not necesarilly the case.

13 Which substance, when dissolved in water,
forms a solution that conducts an electric current?
(1) C2H5OH (3) C12H22O11
(2) C6H12O6 (4) CH3COOH

Try to classify these compounds - there is an alcohol, two carbohydrates and an acid. Which one can dissociate to ions? But this question is IMHO faulty, they want you to think that C6H12O6 is carbohydrate, while it can be something else.

20 In which reaction are electrons transferred from one reactant to another reactant?
(1) 2Ca(s) + O2(g) → 2CaO(s)
(2) AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)
(3) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O( )
(4) H3O+(aq) + OH–(aq) → 2H2O(l)

In what type of reaction are electrons transferred?

29 Which compound has hydrogen bonding between its molecules?
(1) CH4 (3) KH
(2) CaH2 (4) NH3

For the hydrogen bonding you need two things, can you name them? Only one molecule here has them both.

46 The organic compound represented by the condensed structural formula CH3CH2CH2CHO
is classified as an
(1) alcohol (3) ester
(2) aldehyde (4) ether

You just have to know basic characteristic of all listed compounds.

[Borek]

BTW: what in NYS Regents?

[Arkcon]

Check it out here: http://en.wikipedia.org/wiki/New_York_State_Regents  There are also links at the bottom of the page to other US states that have standardized tests required of high school students.  Basically, this is like the UK O-level questions we had before.

[Borek]

Thanks. Honestly, I was just too lazy to google.