Understanding Ionic Equations: Pb2+ & I- Reactants

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In summary: Knowing what reacts and when is what chemistry is about. Some things you just have to remember - H+ + OH- is a neutralization reaction, quite common.
  • #1
Janiceleong26
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Homework Statement


An ionic equation is an equation that shows the chemical species that actually take part in a reaction.
Ex. Pb(NO3)2 (aq) + 2KI (aq) -> PbI2 (s) + 2KNO3 (aq)
So the ionic equation for this reaction is
Pb2+ (aq) + 2I- (aq) -> PbI2 (s)
How do we know that Pb2+ and I- takes part in the reaction? What about K+ and NO3- ?

Homework Equations

The Attempt at a Solution

 
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  • #2
KNO3 is pretty soluble. So is KI. Perhaps Pb(NO3)2 as well. So except the ions that precipitate, the ions in solution don't even notice what's "happening".
 
  • #3
BvU said:
KNO3 is pretty soluble. So is KI. Perhaps Pb(NO3)2 as well. So except the ions that precipitate, the ions in solution don't even notice what's "happening".
Ok...then what about NaOH (aq) + HCl (aq) -> NaCl (aq) + H2O (l)
How do we know that H+ and OH- are the ions that react? And not Na+ and Cl-?
 
  • #4
We know because -- if everything happens in solution, so full ionization (*) and no solids --
the NaOH (aq) on the left stands for Na+ plus OH-
The HCl (aq) on the left for H+ plus Cl-
NaCl (aq) on the right stands for Na+ plus Cl-
And if we leave out the common things on left and right all that happens is H+ + OH- → H2O

So much for the simplistic answer. Reality is a lot more complex, but this case can be untangled by considering it as a set of equilibria:

NaOH (aq) ↔ Na+ + OH-
HCl (aq) ↔ H+ + Cl-
H2O ↔ H+ + OH-
with an equilibrium constant for each of these.
And the k for water is so small compared to the other two that it makes the last equilibrium reaction "shift" to the left.
 
  • #5
Knowing what reacts and when is what chemistry is about. Some things you just have to remember - H+ + OH- is a neutralization reaction, quite common.

What do the solubility rules say about NaCl solubility? Do you expect it to precipitate?
 
  • #6
BvU said:
We know because -- if everything happens in solution, so full ionization (*) and no solids --
the NaOH (aq) on the left stands for Na+ plus OH-
The HCl (aq) on the left for H+ plus Cl-
NaCl (aq) on the right stands for Na+ plus Cl-
And if we leave out the common things on left and right all that happens is H+ + OH- → H2O

So much for the simplistic answer. Reality is a lot more complex, but this case can be untangled by considering it as a set of equilibria:

NaOH (aq) ↔ Na+ + OH-
HCl (aq) ↔ H+ + Cl-
H2O ↔ H+ + OH-
with an equilibrium constant for each of these.
And the k for water is so small compared to the other two that it makes the last equilibrium reaction "shift" to the left.
Oh I see. Thanks!
 
  • #7
Borek said:
Knowing what reacts and when is what chemistry is about. Some things you just have to remember - H+ + OH- is a neutralization reaction, quite common.

What do the solubility rules say about NaCl solubility? Do you expect it to precipitate?
Nope.. Ok I think I've got it thanks
 

1. What is an ionic equation?

An ionic equation is a chemical equation that shows the formation, dissociation, or precipitation of ionic compounds in a reaction. It includes only the ions that are involved in the reaction and omits any spectator ions.

2. How do I identify reactants in an ionic equation?

In an ionic equation, the reactants are typically written on the left side of the arrow. They are the compounds or elements that undergo a chemical change during the reaction.

3. Why are Pb2+ and I- commonly used in ionic equations?

Pb2+ and I- are commonly used in ionic equations because they are both highly reactive ions that readily form compounds. They also have a wide range of applications in various industries, making them important for scientific study.

4. How do I balance an ionic equation?

To balance an ionic equation, you need to make sure that the number of each type of ion on both sides of the equation is equal. This can be done by adjusting the coefficients (numbers in front of the chemical formulas) until the equation is balanced.

5. What is the purpose of understanding ionic equations?

Understanding ionic equations is important in chemistry because they allow us to accurately represent the chemical reactions that occur in solution. They also help us predict the products of a reaction and determine the amount of reactants needed for a desired outcome.

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