Verifying Reasoning for AQ Solutions and Water's Presence in Net Ionic Equations

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In summary, the acid HBr forms ions H and NH3 which leaves Br all alone. But Br can't exist by itself, so it becomes Br2.
  • #1
ktpr2
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i would like to see if my reasoning is correct (for aq. solutions):

[tex]2HBr_(aq_) + 2NH_3_(aq_) -> 2NH_4_(aq_) + Br_2_(aq_) [/tex]
HBR is an acid so it gives H to NH3, which leaves Br all alone. But Br can't exist by itself, so it becoems Br2?
ionic:
[tex]2H^+_(aq_) + 2Br^-_(aq_) + 2NH^-_3_(aq_) -> 2NH^+_4_(aq_) + 2Br^-_(aq_) [/tex]
net ionic:
[tex]2H^+_(aq_) + 2NH^-_3_(aq_) -> 2NH^+_4_(aq_) [/tex]

Also, I have a question about water and its presence or lackthereof in net ionic equations (for aq. solutions).

I have
[tex]2HClO_4_(aq_) + Mg(OH)_2_(s_) -> Mg(ClO_4)_2 (s) + 2H_2O[/tex]
ionic:
(matter states are same as above)[tex]2H^+ + 2CLO^-_4 + Mg^+^2 + 2OH^- -> Mg(ClO_4)_2 + 2H^+ + 2OH^- [/tex]

but that last part is really [tex]2H_2O[/tex]. But if i write it like that, then in my net equation i got to keep [tex]H_2O[/tex] and the H and OH ... making my net equation the same as my ionic equation. That seems wrong to me. Is there a covention where I can write [tex]2H_2O[/tex] and still leave out OH and H as spectator ions in my net ionic equation? Thank you for your time.
 
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  • #2
First check if [itex]Mg(ClO_4)_2[/itex] is a solid, otherwise it would remain hydrated and would not appear in the net ionic equation. And I believe that water will actually be in the net ionic equation, that is [itex]H^+_{(aq)} + OH^-_{(aq)} \xrightarrow{\leftarrow} H_2O_{(l)}[/itex], there's a equilibrium associated with this equation although not on a large scale.
 
  • #3
that is most of the ionized hydrogen cation and hydroxide will be converted to water.
 
  • #4
ERROR - yeah that mg clo4 is solid, it has (s) in subscript beside it.
EDIT - whoops. That was my assumption. If HCLO is breaking it down, then it'd have to be a liquid, as this kind of reaction goes to completion.

That makes the net equation for (2)
[tex]2H^+ + 2CLO^-_4 + Mg^+^2 + 2OH^- -> Mg(ClO_4)_2_(aq_) + 2H_2O[/tex]

I take it the reasoning in my first equation involving HBr and NH3 is correct?
 
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  • #5
First, think about it...how is bromine gas even formed? You've got two anions, the two cannot combine unless one of them is a cation. So bromine anion is the final product, usually the ammonium cation interacts ionically with bromine anion to a degree to form a salt adduct (l). However, I don't believe that you need to get this technical here. Thus your net ionic equation seems correct.
 
  • #6
thanks for your help.
 

1. How can I verify the reasoning for AQ solutions and water's presence in net ionic equations?

To verify the reasoning for AQ solutions and water's presence in net ionic equations, you can use the following steps:

  • Identify the reactants and products in the equation.
  • Determine if any of the reactants or products are aqueous solutions.
  • If there are aqueous solutions, determine if they are strong or weak electrolytes.
  • If the solutions are strong electrolytes, they will dissociate completely in water and can be written as ions.
  • Include all ions that are present in the solutions in the net ionic equation.
  • Balance the charges and verify that the net ionic equation is correct.

2. Why is it important to include water in net ionic equations?

Water is often included in net ionic equations because it is a solvent and can play a role in the reaction. It can also help to balance charges and clarify the chemical species involved in the reaction. Additionally, water molecules can act as proton donors or acceptors, which can affect the overall outcome of the reaction.

3. How do you know if a substance is a strong or weak electrolyte?

A strong electrolyte is a substance that completely dissociates into ions when dissolved in water. This means that all of the substance is in the form of ions in the solution. Examples of strong electrolytes include strong acids and bases, as well as salts. A weak electrolyte is a substance that only partially dissociates into ions when dissolved in water. This means that some of the substance remains in its molecular form in the solution. Examples of weak electrolytes include weak acids and bases, as well as some salts.

4. Can net ionic equations be used to predict whether a reaction will occur?

Net ionic equations cannot be used to predict whether a reaction will occur. They only show the chemical species involved in a reaction and do not take into account factors such as temperature, pressure, and concentration. To predict if a reaction will occur, you would need to use the principles of thermodynamics and kinetics.

5. Are net ionic equations always balanced?

Yes, net ionic equations are always balanced. This means that the number of each type of atom on the reactant side must be equal to the number of that same type of atom on the product side. Additionally, the overall charge on each side of the equation must be the same.

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