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Homework Help: NaOH Vs C2H5-OH

  1. Jan 13, 2018 #1

    navneet9431

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    • 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: Jan 13, 2018
  2. jcsd
  3. Jan 13, 2018 #2

    Borek

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    Have you heard about ionic bonds and covalent bonds?
     
  4. Jan 13, 2018 #3

    navneet9431

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    Yes
     
  5. Jan 13, 2018 #4

    Borek

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    So try to think in these terms. What do you know about compounds involved, how should they behave in water?
     
  6. Jan 13, 2018 #5

    navneet9431

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    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?
     
  7. Jan 13, 2018 #6

    Borek

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    You have ignored the part about ionic and covalent bonds. Can you classify these compounds as ionic or covalent?
     
  8. Jan 13, 2018 #7

    symbolipoint

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    Sodium ions and hydroxide ions; strongly ionized

    Acetate and hydronium ions; weakly ionized
     
  9. Jan 13, 2018 #8

    navneet9431

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    1. The problem statement, all variables and given/known data
    Two elements ##NaOH##(Base) and ##C_2H_5OH##(Alcohol)
    2. Relevant equations
    ##NaOH(s)--->Na+(aq) + OH^{-} (aq)~ and~C_2H_5OH+H_2O--->C_2H_6O+H_2O##
    3. 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.
     
  10. Jan 13, 2018 #9

    Wrichik Basu

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    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.
     
  11. Jan 14, 2018 #10

    navneet9431

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    ##NaOH## is ionic bond whereas ##C_2H_5OH## is a covalent bond.
    But,how is this thing going to answer my question?
     
  12. Jan 14, 2018 #11

    symbolipoint

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    How? This is how:
     
  13. Jan 14, 2018 #12

    navneet9431

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    Then, why is it that strongly ionized substance break into ions but weakly ionized substances do not?
     
  14. Jan 14, 2018 #13

    navneet9431

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    I am a high school student and i do not know anything about "dielectric constant".
    Also, what is this term called "hydration energy".

    Please provide an explanatory answer.
     
  15. Jan 14, 2018 #14

    Wrichik Basu

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    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.
     
  16. Jan 14, 2018 #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.

    Correction : ethanol is highly soluble in water due to hydrogen bonding with water molecules.
     
  17. Jan 14, 2018 #16

    Borek

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    Have you tried to google these terms?

    Please show you are trying to learn on your own, nobody is going to spoonfeed you.
     
  18. Jan 14, 2018 #17

    symbolipoint

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    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.
     
  19. Jan 15, 2018 #18

    Ygggdrasil

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    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.
     
  20. Jan 28, 2018 #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)
     
  21. Jan 28, 2018 #20

    Borek

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    Define "ionic solvent".

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

    Dissociation is a different process from dissolution.
     
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