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Provide the conjugate acid of the following base: CH3CH2OH

Hey everyone :)  I'm getting ready for my first Organic test this Monday (Wish me luck!), and I am having trouble with a couple questions.

1) Provide the conjugate acid of the following base: CH3CH2OH

I chose a)  CH3-CH2-OH2+...Now my thinking was, if CH3CH2OH is a base, it has to donate a lone pair of electrons...meaning O needs to bond to another H+....

The key says that c) CH3-CH2-O- is the correct answer...but this indicates that the molecule acted as an ACID and gained an e- pair from the H atom...I think he may have marked the wrong one...

2)  Which of the following is most likely to behave as a lewis acid?

a)NH3  b)AlCl3  c)PBr3  d)CF3-

Now I eliminated A and D because they have no vacant orbitals to accept and e- pair.  Being left with B and C, I chose B because it had the lower e- negativity (Opps now that I've typed this out I see my error...should have chosen the one with higher e- negativity, right?)  Meaning C is the correct answer.

3)  Which is more stable?

a) CH3O-    b)  HC(=O)-O-

Now the only distinct features are:

1)  B has a double bonded O to the central atom.

I don't really even have a hunch to this though was that since B has 2 O atoms...they'd both carry a negative charge and repel eachother making the molecule unstable... but that is obviously incorrect as the correct answer is B..Any insight here would be much appreciated---I'm obviously missing a concept.

4)  Alkanes are ________ dense than/as water

a) more  b) less  c) as

Okay...d=m/v, but where does this play in?  The most simple alkane, methane...CH4 has a mass of about 16g/mole, where as H2O has a mass of about 18g/mole.  Now assuming they both occupy the same volume...water is more dense....But what about anything larger than methane....then the alkane is more how am I supposed to determine this?

5)  Energy is released when bonds are broken.

a) true  b) false.

I'm really frustrated with this question.  Teachers need to stop asking this, the answer tends to change from person to person.

Now is it not true that:  Energy needs to be put into a bond to break a bond...BUT  after it is broken, some energy is released?

Now, I'm not saying that the system will have an overall energy gain, as more energy may be needed to break the bond than what is released....(would this be endergonic?)

Anyways...He says that enery is NOT relesed when bonds are broken..and would like to defy all cases of where ATP-->  Energy+ADP in our bodies...


Thanks for everyone's help!!

Chemistry Tutor Sat, 09/20/2008 - 11:53

Whats up DJ

I am not organic teacher but I can give you my thoughts

1) the conjugate acid of the base CH3CH2OH

you just need to add an H+


2) NH3 is the classic example of a lewis base

lewis acids accept electron pairs , NH3 has an electron pair to give

PBr3 has the same molecular geometry and lewis structure as NH3 so the same reason above. it will behave as a lewis base

i would says AlCl3

typically metal centers are good lewis acids (think coordinatino complexes accept ligands, which are lewis bases)


i dont remember how to explain this

4) most oils and gases are alkanes

gas floats on water, so it is less dense

valdorod Sat, 09/20/2008 - 20:13

small alcohols behave a lot like water, and as such they are both weakly acidic and weakly basic.  As weak lewis bases they are reversibly protonated by acids to yield oxonium ions, ROH2+.

3.a) CH3O-    b)  HC(=O)-O-
b is the base of formic acid, it is the formate ion, thus it is quite stable in solution, think sodium formate.  a is the base of methanol, and the bases of alcohols are very reactive (i.e. unstable)

Density has very little to do with molar mass.  The first 4 alkanes are all gases at room temperature, while water is a liquid.  By definition gases are less dense than liquids.  The liquid alkanes don't begin until 5 carbons (pentane) which has a density of 0.63 g/ml.  When comparing similar sized molecules, in terms of molar mass, water exhibits hydrogen bonding which is much stronger than the dispersion forces exhibited by the smaller alkanes. 
Eventually with enough carbons the molecule is heavy enough to be a liquid at room temperature.  and even then most alkanes below 10 carbons all have densities less than that of water.

5.  Breaking bonds always requires energy, the process is always endothermic, the breaking of bonds never releases energy.
Formation of bonds always releases energy, the process is always exothermic.  Formation of bonds always releases energy.

The overall enrgy released or absorbed during a reaction, however, is more than just breaking and forming bonds.  Enthalpy is only one factor in the equation, entropy and other factors also affect what the overall energy change will be.

Your teacher is not defying nature, in the case of ATP-ADP the hydrolysis of these molecules is the biggest factor.  The breaking of the phosphate group still requires energy.  The ATP-ADP process does not release energy due to the breaking of one bond, it is much more than that and it is not one reaction but a series of reactions, whose total energy is exothermic.

At the end it is the hydrolysis of ATP that provides the extra energy.

Glucose + ATP4-    [glucose phosphate]- + ADP3-    ?G = -16.7 kJ

The ATP molecule is able to release a lot of energy when it is hydrolyzed because the high charge repulsion in the triphosphate portion of ATP is reduced by the loss of one phosphate and the free HPO42- that is formed is stabilized by delocalization of its pi electrons.

SchoolBoyDJ Sat, 09/20/2008 - 21:32

For 3, I figured it out.  Resonance structures make the negative charge "space" out over the 2 O atoms =DDDD

Thanks for the extra info Valdo...I guess I'll yell at my Bio teachers rather than my chem ones xD

chrisf Sun, 09/21/2008 - 00:05

SchoolBoyDJ wrote:

For 3, I figured it out.  Resonance structures make the negative charge "space" out over the 2 O atoms =DDDD

Which is more reactive: a or b?