Question

Do we write net ionic equations only when there is a solid in the products?

Answer 1

No. One product of a double replacement reaction (also called double displacement and metathesis) must be a solid (precipitate), an insoluble gas, or water. We can write net ionic equations for all of these.

However, if there is no precipitate, gas, or water formed, you would write NR for no reaction and there would be no net ionic equation.

Explanation:

One product of a double replacement reaction (also called double displacement and metathesis) must be a solid (precipitate), an insoluble gas, or water. We can write net ionic equations for all of these.

Example 1: Reaction between aqueous potassium chloride and aqueous lead(II) nitrate with one product as precipitate. This is also called a precipitate reaction.

Molecular equation

`"2KCl(aq) + Pb(NO"_3)_2("aq")"` `rarr` `"2KNO"_3("aq") + "PbCl"_2("s")"`

Net ionic equation: contains only the ions that reacted and their product.

`"2Cl"^(-)("aq") + "Pb"^(2+)("aq")` `rarr` `"PbCl"_2("s")"`

Example 2: Reaction between aqueous hydrochloric acid and aqueous sodium hydroxide in which water is a product. This is a neutralization reaction.

Molecular equation

`"HCl(aq) + NaOH(aq)"` `rarr` `"NaCl(aq) + H"_2"O("l")"`

Net ionic equation

`"H"^(+)("aq") + "OH"^(-)("aq")"` `rarr` `"H"_2"O("l")"`

Example 3: Reaction between iron(II) sulfide and hydrochloric acid in which a gas is a product

Molecular equation

`"FeS(s) + 2HCl(aq)"` `rarr` `"FeCl"_2("aq") + "H"_2"S(g)"`

Net ionic equation

`"FeS(s) + 2H"^(+)("aq")"` `rarr` `"H"_2"S(g)"`

Example 4: Reaction between sodium chloride and potassium nitrate. Actually, there will be no reaction `("NR")` because a precipitate, gas, or water is not formed. You just have a mixture of sodium, potassium, chloride, and nitrate ions.

`"NaCl(aq) + KNO"_3("aq")"` `rarr` `"NR"`

`"NaCl(aq) + KNO"_3("aq")"` `rarr` `"Na"^(+)("aq") + "Cl"^(-)("aq") + "K"^(+)("aq") + "NO"_3^(-)("aq")"`