Complete and balance the precipitation reactions. Include physical states. Refer to the solubility rules as necessary.
precipitation reaction: K3PO4(aq)+MgCl2(aq)⟶?
I know it would require a double replacement so it would be KCl+Mg(PO)4
But how do I know the coefficients and/or subscripts?
K3PO4(aq) + MgCl2(aq)⟶? KCl+Mg(PO)4 (not correct).
Yes, you're right, it is a double replacement reaction and your products are correct but the formula for magnesium phosphate should be Mg3(PO4)2
K3PO4(aq) + MgCl2(aq)⟶ KCl(aq) + Mg3(PO4)2(s)
Equations of this type are balanced by inspection and everyone does it a different way. I'll go through it and you can ask questions if necessary.
I look and see 3K on the left so place a 3 in front of KCl (you will need to change that later). You see 3 Mg on the right side so place a 3 for Mg on the left. You see a 2 PO4 on the right so place a 2 in front of K3PO4. Yes, that messes up the K that you fixed at the beginning so change that 3 you had for KCl to a 6 and you'll be OK. If I were doing this I have enough experience to know that would happen and I would have started with Mg3(PO4)2 initially. The correct equation is
2K3PO4(aq) + 3MgCl2(aq)⟶ 6KCl(aq) + Mg3(PO4)2(s)
Now you check the final equation to make sure everything is OK.
I see 6K left and right.
I see 2 PO4 left and right.
I see 3 Mg left and right.
I see 6 Cl left and right.
Done. Don't forget that last step of checking. That way you will ALWAYS know if the equation is balanced correctly or not.
Well, if you're looking for a balanced and complete precipitation reaction, then we need to check the solubility rules first.
Let's start with the first compound, K3PO4. According to the solubility rules, all alkali metal (Group 1) salts are soluble, so K3PO4 is also soluble. Therefore, it remains as K3PO4(aq).
Moving onto the next compound, MgCl2. Chlorides (except for those of silver, lead, and mercury) are generally soluble. Therefore, MgCl2 is also soluble and stays as MgCl2(aq).
Since both compounds are soluble, there will be no precipitation occurring. This means that no reaction occurs between K3PO4 and MgCl2, and the complete and balanced equation would be:
K3PO4(aq) + MgCl2(aq) ⟶ no reaction
Seems like in this case, the precipitation is actually a no-show. It happens sometimes—nature can be quite unpredictable!
To balance the precipitation reaction, you need to determine the correct coefficients and subscripts for the balanced equation.
1. Write down the unbalanced equation:
K3PO4(aq) + MgCl2(aq) ⟶ ? (unknown products)
2. Identify the ions present in each compound:
K3PO4 dissociates into 3K+ ions and 1PO4^3- ion.
MgCl2 dissociates into 1Mg^2+ ion and 2Cl- ions.
3. Determine the possible products by swapping the positive and negative ions:
The positive ion from K3PO4 (K+) can combine with the negative ion from MgCl2 (Cl-) to form KCl.
The positive ion from MgCl2 (Mg^2+) can combine with the negative ion from K3PO4 (PO4^3-) to form Mg3(PO4)2.
So, the balanced equation is:
K3PO4(aq) + MgCl2(aq) ⟶ 3KCl(aq) + Mg3(PO4)2(s)
Note: The compounds KCl and Mg3(PO4)2 are both soluble in water and will dissociate into ions (aq). However, Mg3(PO4)2 is insoluble in water and forms a solid (s) precipitate.
To balance the precipitation reaction, you need to determine the coefficients and subscripts based on the stoichiometry of the reaction. Here's how you can do it step by step:
Step 1: Write the balanced chemical equation using the provided reactant compounds:
K3PO4(aq) + MgCl2(aq) ⟶ KCl + Mg(PO)4
Step 2: Check the solubility rules to determine if any of the compounds are insoluble and will form a precipitate. According to the solubility rules, most phosphates (PO4) are insoluble except for alkali metals (Group 1 elements) and ammonium (NH4+). In this case, K3PO4 is soluble while MgCl2 is soluble.
Step 3: Since there is a possible precipitate formed, swap the positive ions (metal cations) between the compounds while keeping their respective charges. The resulting equation becomes:
K3PO4(aq) + MgCl2(aq) ⟶ KCl(aq) + Mg3(PO4)2
Step 4: Now, check if the equation is balanced. Count the number of atoms of each element on both sides.
K: 3 on the left, 1 on the right
P: 1 on the left, 2 on the right
Mg: 1 on the left, 3 on the right
Cl: 2 on the left, 1 on the right
The equation is currently not balanced.
Step 5: To balance the equation, multiply the compounds with the lowest number of atoms by the appropriate coefficients. In this case, we need to multiply KCl by 3, and Mg3(PO4)2 by 2 to balance the number of atoms.
The balanced and complete equation is:
K3PO4(aq) + 3MgCl2(aq) ⟶ 3KCl(aq) + 2Mg3(PO4)2
Make sure to include the state symbols (aq for aqueous and s for solid) to indicate the physical states of the reactants and products.
Final balanced and complete equation with state symbols:
2 K3PO4(aq) + 3 MgCl2(aq) ⟶ 6 KCl(aq) + Mg3(PO4)2(s)