Video Transcript
A precipitate of barium sulfate can be formed by reacting barium chloride with magnesium sulfate. What is the symbol equation, with state symbols, for this reaction? What is the net ionic equation?
The question tells us that the reaction taking place will form a precipitate. This means the reaction is a precipitation reaction, which can be defined as a reaction that forms an insoluble solid product from the reaction between two soluble substances in solution. This means the two reactants are soluble in water, which we can represent using the state symbol aq, which stands for aqueous. When these two soluble substances react, an insoluble solid product will form, which is the precipitate, which will be assigned in the symbol equation with a state symbol of s, standing for solid. Precipitation reactions also usually form other products that are water-soluble and given the state symbol aq.
Using this pattern as a guide, let’s begin writing our symbol equation. We are told that barium chloride and magnesium sulfate are the reactants. Let’s begin the equation by writing the chemical formula for barium chloride. Barium chloride is an ionic compound and will be composed of barium ions and chloride ions. To write the chemical formula for barium chloride, we will utilize subscripts to show the ratio of ions needed for the compound to be neutral overall. For every one barium ion, the compound will contain two chloride ions. So, the chemical formula of barium chloride is BaCl2. Note that subscripts of one are implied and are not written in chemical formulas.
Since barium chloride is a reactant in this precipitation reaction and it is soluble in water, we will assign it a state symbol of aq for aqueous. Let’s now write the chemical formula for our second reactant magnesium sulfate. Magnesium sulfate will be composed of magnesium ions and sulfate ions with a chemical formula of MgSO4 representing that in this compound for every one magnesium ion, there is one sulfate ion present. As the second reactant in this precipitation reaction and a water-soluble compound, we can assign the state symbol aq.
Let’s finish this symbol equation by writing the chemical formulas of the products. Let’s begin with the product given, barium sulfate. Barium sulfate will be composed of barium ions and sulfate ions with a chemical formula of BaSO4. We are told that barium sulfate is the precipitate formed in this reaction, which means that it is the product which is an insoluble solid, so we can assign it the state symbol s. Finally, we can deduce the chemical formula of the second product by looking to the reactants to see which ions remain. This product will contain the remaining magnesium ions and chloride ions with the compound containing one magnesium ion for every two chloride ions, resulting in a chemical formula of MgCl2. As the second product in a precipitation reaction and a water-soluble compound, we can assign it the state symbol aq.
To confirm that our symbol equation is balanced, we can compare the amount of each ion present in the reactants to the amounts present in the products, which we can see are equal. So our equation is indeed balanced. We have now answered the question “What is the symbol equation, with state symbols, for this reaction?” with our equation BaCl2 aqueous plus MgSO4 aqueous react to form BaSO4 solid plus MgCl2 aqueous.
Now that we have written the symbol equation for this reaction, we can answer the question “What is the net ionic equation?” Our symbol equation can also be called a molecular equation, which represents all formulas as molecules. For example, barium chloride is expressed as BaCl2, which might bring to mind particles of barium chloride with one barium ion and two chloride ions adhering together. However, as a water-soluble compound in an aqueous solution, the ionic compound will be dissolved with the ions separating in solution. We can more accurately represent this behavior using an ionic equation which represents formulas of aqueous solutions as individual ions. The ionic equation will lead us to the net ionic equation to answer this question, which includes only the species that undergo chemical change.
Let’s now write the ionic equation. We must first identify all the species in the molecular equation that are aqueous. Then, we will split each of them into their constituent ions, which must retain the aqueous state symbol, and we must accurately reflect how many ions are present using coefficients. So, BaCl2 aqueous from the molecular equation becomes Ba2+ aqueous plus two Cl− aqueous. We will repeat this process for the remaining aqueous reactant and for the aqueous product. Now, for our solid product barium sulfate, we will leave the chemical formula exactly as written in the molecular equation, since it is insoluble and would not break apart into its constituent ions.
Now that we have completed the ionic equation, we are ready to write the net ionic equation. We will do this by eliminating what are called spectator ions from the ionic equation, which exist as reactants and products in an ionic equation but do not take part in the chemical reaction and are therefore not included in the net ionic equation. To identify spectator ions, we must look for species that appear in the same form in the reactants as they do in the products, which means they have not undergone chemical change, and we will not include them in the net ionic equation.
Magnesium ions are spectators in this reaction as are two chloride ions. This means the remaining species that do undergo chemical change and will be included in the net ionic equation are barium ions and sulfate ions as reactants with solid barium sulfate as the only product. As with any other chemical equation, we can confirm our net ionic equation is written correctly by checking that it is properly balanced and that the sum of the charges of the reactants is equal to the sum of the charges of the products.
We have now answered the question “What is the net ionic equation?” Our net ionic equation for this reaction is Ba2+ aqueous plus SO42− aqueous react to form BaSO4 solid.
