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Topic: Which of the following statements about alcohols is true?  (Read 3931 times)

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UOIT

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Which of the following statements about alcohols is true?
« on: October 22, 2007, 01:05:57 PM »
Which of the following statements about alcohols is true?

a. They can associate by hydrogen bonding.

 b. They are Bronsted bases.

 c. They are Bronsted acids.

 d. All of the above.

 e. A and C.

I said D....Am I correct

Offline AWK

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Re: Which of the following statements about alcohols is true?
« Reply #1 on: October 22, 2007, 01:34:47 PM »
OK
AWK

Offline ace

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Re: Which of the following statements about alcohols is true?
« Reply #2 on: October 22, 2007, 08:21:10 PM »
You are correct.   That said, do you know why your answer is the correct one?   Let's think abou it a bit.   For example:

In an O-H bond, the O steals the H's electron due to its electronegativity, and O can carry a negative charge (R-O-). This leads to deprotonation in which the nucleus of the H, a proton, leaves completely. This makes the -OH group (and alcohols) Bronsted acids. Alcohols are weak acids, even weaker than water. Ethanol has a pKa of 15.9 compared to water's pKa of 15.7. The larger the alcohol molecule, the weaker an acid it is.
On the other hand, alcohols are also weakly basic. This may seem to be contradictory--how can a substance be both an acid and a base? However, substances exist that can be an acid or a base depending on the circumstances. Such a compound is said to be amphoteric or amphiprotic. As a Bronsted base, the oxygen atom in the -OH group can accept a proton (hydrogen ion.) This results in a positively-charged species known as an oxonium ion. Oxonium ions have the general formula ROH2+, where R is any alkyl group.

Also alcohols tend to be soluble in water.  That alone, especially for simpler alcohols like methanol or ethanol should be a hint.   The solubility is due to hydrogen bonding with water.   

Hope this helps.

UOIT

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Re: Which of the following statements about alcohols is true?
« Reply #3 on: October 22, 2007, 10:25:26 PM »

Thank you Ace ;D

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