1. Double Replacement Reactions
Vocabulary
Double Replacement Reaction

2. Review Q: What happens in a double replacement reaction?
A: Ions from two different ionic compounds switch places
Q: In what state must the ionic compounds be in order to participate in a double replacement reaction?
A: aqueous

3. Practice
Write the equation for the reaction between aqueous sodium chloride and aqueous lead(II) nitrate.

4. Step 1 Write the formulas for each of the reactants. NaCl (aq) +
Pb(NO3)2 (aq)

5. Step 2 NaCl (aq) + Pb(NO3)2 (aq) → PbCl2 + NaNO3
Swap cations and write formulas for each product.
NaCl (aq) +
Pb(NO3)2 (aq) →
PbCl2 +
NaNO3

6. Reminder
You get the formulas for the products by swapping the charges of the ions.
NaCl (aq) +
Pb(NO3)2 (aq) →
PbCl2 +
NaNO3

7. Step 3 Balance the equation. 2 NaCl (aq) + Pb(NO3)2 (aq) → PbCl2 + 2
NaNO3

8. Now what?
An important part of writing double replacement reactions is determining if the reaction will occur or not. To do this, we need to identify the states of the products using the solubility chart. 2
NaCl (aq) +
Pb(NO3)2 (aq) →
PbCl2 (?) + 2
NaNO3 (?)

9. Predicting solubility
Let’s first look at the lead(II) chloride. According to the solubility chart, is it soluble or insoluble in water?
PbCl2 (?)

10. Predicting solubility
It looks like it’s insoluble meaning that it is a solid when in water. The ions are not free to move around the solution and you will see it as a precipitate.
PbCl2 (s)

11. Predicting solubility
Let’s now look at the solubility of the other product in this reaction, sodium nitrate.
NaNO3 (?)

12. Predicting solubility
This one looks like it’s soluble. That means that the ions remain dissociated in the solution. You will not see this compound form in this reaction.
NaNO3 (aq)

13. Predicting solubility
Because at least one of the products is a solid, this reaction WILL occur. You will see the lead(II) chloride precipitate which is evidence of a chemical reaction. 2
NaCl (aq) +
Pb(NO3)2 (aq) →
PbCl2 (s) + 2
NaNO3 (aq)

14. In order for a double replacement reaction to occur, at least one of the products must be a solid. If both products remain aqueous, no reaction occurs.

15. Practice
Write the balanced chemical equation for the reaction between aqueous copper(II) sulfate and aqueous rubidium carbonate and predict if the reaction occurs or not.

16. Step 1: Write reactant formulas
CuSO4(aq) + Rb2CO3(aq) →

17. Step 2: Swap cations and write formulas for products
CuSO4(aq) + Rb2CO3(aq) →
Rb2SO4(?) + CuCO3(?)

18. Step 3: Balance the equation
CuSO4(aq) + Rb2CO3(aq) →
Rb2SO4(?) + CuCO3(?)
The equation is already balanced.

19. Step 4: Predict states of products
CuSO4(aq) + Rb2CO3(aq) →
Rb2SO4(?) + CuCO3(?)

20. Step 4: Predict states of products
CuSO4(aq) + Rb2CO3(aq) →
Rb2SO CuCO3(?)
(aq)

21. Step 4: Predict states of products
CuSO4(aq) + Rb2CO3(aq) →
Rb2SO4(aq) + CuCO3(?)

22. Step 4: Predict states of products
CuSO4(aq) + Rb2CO3(aq) →
Rb2SO4(aq) + CuCO3
(s)

23. Conclusion: Does the reaction occur?
CuSO4(aq) + Rb2CO3(aq) →
Rb2SO4(aq) + CuCO3(s)
The reaction does occur because one of the products is a solid.

24. Last Practice: On Your Own
When a solution of potassium hydroxide is mixed with a solution of barium nitrate, will a reaction occur?

25. Last Practice: On Your Own
2 KOH (aq) + Ba(NO3)2 (aq) →
2 KNO3 (aq) + Ba(OH)2 (aq)
No reaction because both products are aqueous