Choose the net ionic equation for the formation of the product in Step 5. Select the best answer.
$Mg ^{2+}(a q)+2 NH _4^{+}(a q) \rightarrow Mg \left( NH _4\right)_2(s)$
$Mg \left( NO _3\right)_2(a q)+\left( NH _4\right)_2 C _2 O _4(a q) \rightarrow MgC _2 O _4(s)+2 NH _4 NO _3(a q)$
$Mg \left( NO _3\right)_2(a q)+\left( NH _4\right)_2 C _2 O _4(a q) \rightarrow MgC _2 O _4(s)+\left( NH _4\right)_2\left( NO _3\right)_2(a q)$
$Ca \left( NO _3\right)_2(a q)+\left( NH _4\right)_2 C _2 O _4(a q) \rightarrow CaC _2 O _4(s)+\left( NH _4\right)_2\left( NO _3\right)_2(a q)$
$Mg ^{2+}(a q)+ C _2 O _4{ }^{2 \cdot}(a q) \rightarrow MgC _2 O _4(s)$
$Ca ^{2+}(a q)+ C _2 O _4^{2 \cdot}(a q) \rightarrow CaC _2 O _4(s)$
$Ca \left( NO _3\right)_2(a q)+\left( NH _4\right)_2 C _2 O _4(a q) \rightarrow CaC _2 O _4(s)+2 NH _4 NO _3(a q)$
$Ca ^{2+}(a q)+2 NH _4{ }^{+}(a q) \rightarrow Ca \left( NH _4\right)_2(s)$
Answer (2)
Identify the possible precipitation reactions from the given list of equations.
Write the complete ionic equation for each possible precipitation reaction.
Identify and cancel out the spectator ions from the complete ionic equation to obtain the net ionic equation.
The net ionic equation for the formation of magnesium oxalate is M g 2 + ( a q ) + C 2 O 4 2 − ( a q ) → M g C 2 O 4 ( s ) .
Explanation
Understanding the Problem The question asks us to identify the correct net ionic equation for a precipitation reaction. We are given several options, and we need to determine which one accurately represents the formation of a solid precipitate, excluding spectator ions.
Identifying Precipitation Reactions and Net Ionic Equations Let's analyze the given reactions to identify the precipitation reactions and their corresponding net ionic equations.
M g ( N O 3 ) 2 ( a q ) + ( N H 4 ) 2 C 2 O 4 ( a q ) → M g C 2 O 4 ( s ) + 2 N H 4 N O 3 ( a q )
Complete ionic equation: M g 2 + ( a q ) + 2 N O 3 − ( a q ) + 2 N H 4 + ( a q ) + C 2 O 4 2 − ( a q ) → M g C 2 O 4 ( s ) + 2 N H 4 + ( a q ) + 2 N O 3 − ( a q )
Net ionic equation: M g 2 + ( a q ) + C 2 O 4 2 − ( a q ) → M g C 2 O 4 ( s )
C a ( N O 3 ) 2 ( a q ) + ( N H 4 ) 2 C 2 O 4 ( a q ) → C a C 2 O 4 ( s ) + 2 N H 4 N O 3 ( a q )
Complete ionic equation: C a 2 + ( a q ) + 2 N O 3 − ( a q ) + 2 N H 4 + ( a q ) + C 2 O 4 2 − ( a q ) → C a C 2 O 4 ( s ) + 2 N H 4 + ( a q ) + 2 N O 3 − ( a q )
Net ionic equation: C a 2 + ( a q ) + C 2 O 4 2 − ( a q ) → C a C 2 O 4 ( s )
Comparing Derived and Given Equations Now, let's compare the derived net ionic equations with the given options:
M g 2 + ( a q ) + 2 N H 4 + ( a q ) → M g ( N H 4 ) 2 ( s ) - Incorrect (ammonium is a spectator ion)
M g ( N O 3 ) 2 ( a q ) + ( N H 4 ) 2 C 2 O 4 ( a q ) → M g C 2 O 4 ( s ) + 2 N H 4 N O 3 ( a q ) - Incorrect (this is the full equation, not the net ionic equation)
C a ( N O 3 ) 2 ( a q ) + ( N H 4 ) 2 C 2 O 4 ( a q ) → C a C 2 O 4 ( s ) + ( N H 4 ) 2 ( N O 3 ) 2 ( a q ) - Incorrect (similar to the previous one)
M g 2 + ( a q ) + C 2 O 4 2 − ( a q ) → M g C 2 O 4 ( s ) - Correct (matches our derived net ionic equation for magnesium oxalate)
C a 2 + ( a q ) + C 2 O 4 2 − ( a q ) → C a C 2 O 4 ( s ) - Correct (matches our derived net ionic equation for calcium oxalate)
C a ( N O 3 ) 2 ( a q ) + ( N H 4 ) 2 C 2 O 4 ( a q ) → C a C 2 O 4 ( s ) + 2 N H 4 N O 3 ( a q ) - Incorrect (this is the full equation, not the net ionic equation)
C a 2 + ( a q ) + 2 N H 4 + ( a q ) → C a ( N H 4 ) 2 ( s ) - Incorrect (ammonium is a spectator ion)
Determining the Correct Net Ionic Equation Since the question refers to Step 5, and we have two possible precipitation reactions, we need to consider the context of Step 5 (which is not provided). However, based on the given options, the most likely net ionic equations are:
M g 2 + ( a q ) + C 2 O 4 2 − ( a q ) → M g C 2 O 4 ( s )
C a 2 + ( a q ) + C 2 O 4 2 − ( a q ) → C a C 2 O 4 ( s )
Without additional context, it's impossible to definitively choose between these two. However, if we assume the reaction involves magnesium, the correct answer is:
Final Answer The net ionic equation for the formation of magnesium oxalate is: M g 2 + ( a q ) + C 2 O 4 2 − ( a q ) → M g C 2 O 4 ( s )
Examples
Net ionic equations are useful in environmental chemistry to predict the formation of precipitates in water treatment processes. For example, when treating wastewater containing heavy metal ions, we can use net ionic equations to determine which chemicals to add to precipitate the metal ions as insoluble salts, thereby removing them from the water. This ensures that the treated water is safe for discharge or reuse, protecting aquatic ecosystems and human health. For instance, adding phosphate ions to water containing lead ions will result in the precipitation of lead phosphate, effectively removing lead from the water: 3 P b 2 + ( a q ) + 2 P O 4 3 − ( a q ) → P b 3 ( P O 4 ) 2 ( s ) .
The net ionic equation for the formation of magnesium oxalate is M g 2 + ( a q ) + C 2 O 4 2 − ( a q ) → M g C 2 O 4 ( s ) . This reaction illustrates the precipitation of magnesium oxalate from its ions in solution. Therefore, the correct answer is the option that presents this equation.
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