NaOH vs C2H5OH: Reason for Disassociation

Click For Summary

Discussion Overview

The discussion centers on the differing behaviors of sodium hydroxide (NaOH) and ethanol (C2H5OH) when dissolved in water, specifically why NaOH dissociates into hydroxide ions while ethanol does not. The scope includes theoretical explanations related to ionic and covalent bonding, solvation energy, and the nature of dissolution versus dissociation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants note that NaOH dissociates into hydroxide ions due to its ionic bond with sodium, while ethanol, being covalent, does not dissociate in water.
  • Others discuss the concept of hydration energy and solvation energy, suggesting that NaOH's lattice energy is less than the hydration energy, allowing it to dissociate, whereas ethanol's bond energy is greater than the hydration energy, preventing dissociation.
  • A participant points out that ethanol can partially dissociate in certain reactions but not in plain water, highlighting the complexity of its behavior.
  • There is mention of the differences between ionic and covalent bonds, with emphasis on how water interacts differently with these types of compounds.
  • Some participants express confusion about terms like "dielectric constant" and "hydration energy," seeking clarification.
  • One participant suggests that ionic compounds dissolve in ionic solvents, while ethanol, being an organic compound, does not dissociate in water.
  • Another participant corrects a misunderstanding regarding the solubility of ethanol in water, emphasizing that it does dissolve but does not dissociate like NaOH.

Areas of Agreement / Disagreement

Participants generally agree on the distinction between ionic and covalent compounds and their behaviors in water, but multiple competing views remain regarding the specifics of dissociation and the role of hydration energy. The discussion remains unresolved on certain technical terms and their implications.

Contextual Notes

Some participants express uncertainty about specific scientific terms and concepts, such as "dielectric constant" and "hydration energy," which may limit their understanding of the discussion. There are also unresolved questions about the definitions and implications of dissolution versus dissociation.

Who May Find This Useful

This discussion may be useful for high school students studying chemistry, particularly those interested in the behavior of different types of compounds in solvents, as well as those seeking clarification on ionic and covalent bonding concepts.

navneet9431
Gold Member
Messages
107
Reaction score
9
Please post this type of questions in the homework section using the template and showing your work and what you already know.
If we put NaOH in water then it disassociates into ##OH^{-}## ions(hydroxyl ions) but if we put ##C_2H_5OH## in water it does not disassociates into ##OH^{-}## ions.
What is the reason that ##NaOH## disassociates into ##OH^{-}## ions(hydroxyl ions) whereas ##C_2H_5OH## does not disassociate into ##OH^{-}## ions when dissolved in water?
I will be thankful for help!
NOTE: I am a High School student and English is my second language.
 
Last edited:
Physics news on Phys.org
Have you heard about ionic bonds and covalent bonds?
 
Borek said:
Have you heard about ionic bonds and covalent bonds?
Yes
 
So try to think in these terms. What do you know about compounds involved, how should they behave in water?
 
Borek said:
So try to think in these terms. What do you know about compounds involved, how should they behave in water?
I can only think that both of them will dissolve in water.
But,i can't think why ##NaOH## disassociates into ##H^{-}## ions while ##C_2H_5OH## doesn't?
 
You have ignored the part about ionic and covalent bonds. Can you classify these compounds as ionic or covalent?
 
  • Like
Likes   Reactions: navneet9431
Sodium ions and hydroxide ions; strongly ionized

Acetate and hydronium ions; weakly ionized
 
  • Like
Likes   Reactions: navneet9431

Homework Statement


Two elements ##NaOH##(Base) and ##C_2H_5OH##(Alcohol)

Homework Equations


##NaOH(s)--->Na+(aq) + OH^{-} (aq)~ and~C_2H_5OH+H_2O--->C_2H_6O+H_2O##

The Attempt at a Solution


If we put NaOH in water then it disassociates into ##OH^{-}## ions(hydroxyl ions) but if we put ##C_2H_5OH## in water it does not disassociates into ##OH^{-}## ions.
What is the reason that ##NaOH## disassociates into ##OH^{-}## ions(hydroxyl ions) whereas ##C_2H_5OH## does not disassociate into ##OH^{-}## ions when dissolved in water?
I will be thankful for help!
NOTE: I am a High School student and English is my second language.
 
In ##NaOH##, the ##-OH## group is attached to the ##Na## atom by an ionic bond. As water is an ionic solvent with a high dielectric constant, in water, ##NaOH## dissociates into its respective ions.

##C_2 H_5 OH## is a covalent compound, in which the ##-OH## group is attached by a covalent bond. Water cannot produce enough hydration energy to break the bond, which is why it does not dissociate in water.
 
  • #10
Borek said:
You have ignored the part about ionic and covalent bonds. Can you classify these compounds as ionic or covalent?
##NaOH## is ionic bond whereas ##C_2H_5OH## is a covalent bond.
But,how is this thing going to answer my question?
 
  • #11
navneet9431 said:
##NaOH## is ionic bond whereas ##C_2H_5OH## is a covalent bond.
But,how is this thing going to answer my question?

How? This is how:
symbolipoint said:
Sodium ions and hydroxide ions; strongly ionized

Acetate and hydronium ions; weakly ionized
 
  • #12
symbolipoint said:
How? This is how:
Then, why is it that strongly ionized substance break into ions but weakly ionized substances do not?
 
  • #13
Wrichik Basu said:
As water is an ionic solvent with a high dielectric constant, in water, ##NaOH## dissociates into its respective ions.
I am a high school student and i do not know anything about "dielectric constant".
Wrichik Basu said:
Water cannot produce enough hydration energy to break the bond, which is why it does not dissociate in water.
Also, what is this term called "hydration energy".

Please provide an explanatory answer.
 
  • #14
Forget dielectric constant for the time.

The energy of solvation is the amount of energy associated with dissolving a solute in a solvent. If it is a positive number, the dissolving process is endothermic; if it is negative, it's exothermic. The energy of solvation is sometimes found by comparing the lattice energy (the amount of energy needed to break the bonds of the solute) and the hydration energy (the amount of energy released when the solute particles bond with the solvent).

Hydration energy is a type of solvation energy exclusively for water. It must be greater than lattice energy (for ionic solids) or bond energy (for covalent solids) for the solid to dissolve in water.

For ##NaOH##, the lattice energy < Hydration energy, which is why it dissociates. For ##C_2 H_5 OH## the bond energy > Hydration energy, which is why it is insoluble and does not dissociate in water.
 
  • Like
Likes   Reactions: Buffu
  • #15
##C_2H_5OH+H_2O--->C_2H_6O+H_2O## is wrong.

Ethanol does (partially)dissociate into hydroxyl group and alkyl group, just that this dissociation does not happen in plain water. In nucleophilic substitution reactions (ethanol mainly undergoes SN2) -OH of ethanol is partially dissociated from alkyl group to make way for back attack.

Ethanol is bad at dissociation; other alcohols of higher degree like tert-butyl alcohol dissociates into -OH and carbocation both in SN1 reactions and E1 reactions.

Yes you are correct that ethanol does not dissociate like NaOH - the reason is given by @Wrichik Basu - but that is nothing special of organic molecules, even
-OH group of sulphuric acid doesn't dissociates into -OH and HSO3 in just water.

Wrichik Basu said:
which is why it is insoluble and does not dissociate in water.

Correction : ethanol is highly soluble in water due to hydrogen bonding with water molecules.
 
  • Like
Likes   Reactions: Wrichik Basu
  • #16
navneet9431 said:
I am a high school student and i do not know anything about "dielectric constant".

Also, what is this term called "hydration energy".

Have you tried to google these terms?

Please provide an explanatory answer.

Please show you are trying to learn on your own, nobody is going to spoonfeed you.
 
  • #17
navneet9431 said:
Then, why is it that strongly ionized substance break into ions but weakly ionized substances do not?
False assumption.

Acetic acid is not an ionic compound, although it IS an acid, and it DOES dontate a hydrogen ION in water solution. The compound is NOT COMPLETELY ionized in water.
 
  • #18
Why are people discussing acetic acid and acetate? The organic compound being discussed,C2H5OH, is ethanol.

As navneet9431 noted, the bond between sodium and the OH group in NaOH is an ionic bond whereas the bond between carbon and the hydroxyl group in ethanol is a covalent bond. Ionic bonds are held together by electrostatic interaction (the attraction between the positive charge of the sodium ion and the negative charge of the hydroxide ion) whereas covalent bonds form from the sharing of electrons between the carbon and oxygen atoms forming the bond.

Water is a polar substance that has a slight positive charge on one end and a slight negative charge on the other end. Because of these slight charges, water can disrupt ionic bonds. Instead of interacting with the negative hydroxide ions in a solid crystal of NaOH, the sodium ions are more than happy to interact with the negative ends of the water molecules (the same goes with the hydroxide ions). Water is less good at sharing electrons with other compounds, so it is much less likely that water would displace the hydroxyl group of ethanol by forming a new covalent bond (and such a reaction would just regenerate ethanol anyway).

So, in general, ionic bonds will dissociate in water whereas most covalent bonds will not.
 
  • Like
Likes   Reactions: navneet9431 and jim mcnamara
  • #19
We can also think in this way to make subject easy :- Simple: we know that Ionic compound dissolves in ionic solvents.In such a way NaOH disassociates.
C2H5OH is ethanol ,an organic compound, it dissolves only in organic solvent.
So it doesn't disassociate in water.
(Pls verify my reason with your teacher)
 
  • #20
hyunxu said:
we know that Ionic compound dissolves in ionic solvents.

Define "ionic solvent".

C2H5OH is ethanol ,an organic compound, it dissolves only in organic solvent.

No, it dissolves in water which is not considered an organic solvent.

So it doesn't disassociate in water.

Dissociation is a different process from dissolution.
 
  • Like
Likes   Reactions: symbolipoint
  • #21
Oh.Ok.
 
  • #22
symbolipoint said:
False assumption.

Acetic acid is not an ionic compound, although it IS an acid, and it DOES dontate a hydrogen ION in water solution. The compound is NOT COMPLETELY ionized in water.
Very observant, Ygggdrasil,
I was not careful reading the formula from the posting. My fault.
 
  • #23
symbolipoint said:
False assumption.

Acetic acid is not an ionic compound, although it IS an acid, and it DOES dontate a hydrogen ION in water solution. The compound is NOT COMPLETELY ionized in water.
Not completely ionized means it is a week acid which are used to be organic acids eg:HCOOH , CH3COOH
 
  • #24
hyunxu said:
Not completely ionized means it is a week acid which are used to be organic acids eg:HCOOH , CH3COOH
Yes; but as I recently wrote, I misunderstood/ or MISREAD the text-shown formula on the posting.