$MgCl _2(aq)$ and $Na _3 PO _4(aq)$
$Mg Cl _2( aq ) + Na _3 PO _4( aq ) \rightarrow$ Molecular Equation
Complete Ionic Equation
Net Ionic Equation
Spectator Ions
Answer (1)
The balanced molecular equation is 3 M g C l 2 ( a q ) + 2 N a 3 P O 4 ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + 6 N a Cl ( a q ) .
The complete ionic equation is 3 M g 2 + ( a q ) + 6 C l − ( a q ) + 6 N a + ( a q ) + 2 P O 4 3 − ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + 6 N a + ( a q ) + 6 C l − ( a q ) .
The net ionic equation is 3 M g 2 + ( a q ) + 2 P O 4 3 − ( a q ) → M g 3 ( P O 4 ) 2 ( s ) .
The spectator ions are N a + ( a q ) and C l − ( a q ) .
The final equations and spectator ions are: 3 M g C l 2 ( a q ) + 2 N a 3 P O 4 ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + 6 N a Cl ( a q ) ; 3 M g 2 + ( a q ) + 6 C l − ( a q ) + 6 N a + ( a q ) + 2 P O 4 3 − ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + 6 N a + ( a q ) + 6 C l − ( a q ) ; 3 M g 2 + ( a q ) + 2 P O 4 3 − ( a q ) → M g 3 ( P O 4 ) 2 ( s ) ; N a + ( a q ) an d C l − ( a q )
Explanation
Initial Analysis When magnesium chloride ( M g C l 2 ) reacts with sodium phosphate ( N a 3 P O 4 ) in aqueous solution, a double displacement reaction occurs. This means the cations and anions of the two reactants switch partners. Magnesium phosphate ( M g 3 ( P O 4 ) 2 ) is insoluble in water and precipitates out of the solution. Sodium chloride ( N a Cl ) remains in solution because it is soluble.
Balanced Molecular Equation First, we write the balanced molecular equation, ensuring that the number of atoms of each element is the same on both sides of the equation. The unbalanced equation is:
M g C l 2 ( a q ) + N a 3 P O 4 ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + N a Cl ( a q )
To balance the equation, we need 3 magnesium ions on the left, so we have 3 M g C l 2 . This gives us 6 chloride ions, so we need 6 N a Cl on the right. This means we need 2 phosphate ions on the left, so we have 2 N a 3 P O 4 . The balanced molecular equation is:
3 M g C l 2 ( a q ) + 2 N a 3 P O 4 ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + 6 N a Cl ( a q )
Complete Ionic Equation Next, we write the complete ionic equation. In this equation, we dissociate all aqueous strong electrolytes into their respective ions. Solid magnesium phosphate remains as a solid.
3 M g 2 + ( a q ) + 6 C l − ( a q ) + 6 N a + ( a q ) + 2 P O 4 3 − ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + 6 N a + ( a q ) + 6 C l − ( a q )
Identifying Spectator Ions Now, we identify the spectator ions. These are the ions that appear on both sides of the equation and do not participate in the reaction. In this case, the spectator ions are sodium ions ( N a + ) and chloride ions ( C l − ).
Net Ionic Equation Finally, we write the net ionic equation by removing the spectator ions from the complete ionic equation. This gives us the equation that only includes the species that actually react:
3 M g 2 + ( a q ) + 2 P O 4 3 − ( a q ) → M g 3 ( P O 4 ) 2 ( s )
Final Answer In summary:
Molecular Equation: 3 M g C l 2 ( a q ) + 2 N a 3 P O 4 ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + 6 N a Cl ( a q )
Complete Ionic Equation: 3 M g 2 + ( a q ) + 6 C l − ( a q ) + 6 N a + ( a q ) + 2 P O 4 3 − ( a q ) → M g 3 ( P O 4 ) 2 ( s ) + 6 N a + ( a q ) + 6 C l − ( a q )
Net Ionic Equation: 3 M g 2 + ( a q ) + 2 P O 4 3 − ( a q ) → M g 3 ( P O 4 ) 2 ( s )
Spectator Ions: N a + ( a q ) and C l − ( a q )
Examples
Consider a wastewater treatment plant that needs to remove phosphate ions from the water. Adding magnesium chloride can help precipitate out the phosphate as magnesium phosphate, which can then be filtered out. This process is based on the same chemical reaction we analyzed. Understanding these reactions helps engineers design effective water treatment processes, ensuring cleaner and safer water resources. The principles of solubility and ionic reactions are crucial in environmental chemistry.
