Question

Write balanced net ionic equations for the reactions that occur when the following aqueous solutions are mixed. If no reaction is likely to occur, so indicate. a. silver nitrate, \(\mathrm{AgNO}_{3}\), and potassium chloride, \(\mathrm{KCl}\) b. nickel(II) sulfate, \(\mathrm{NiSO}_{4}\), and barium chloride, \(\mathrm{BaCl}_{2}\) c. ammonium phosphate, \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4},\) and calcium chloride, \(\mathrm{CaCl}_{2}\) d. hydrofluoric acid, \(\mathrm{HF}\), and potassium sulfate, \(\mathrm{K}_{2} \mathrm{SO}_{4}\) e. calcium chloride, \(\mathrm{CaCl}_{2}\), and ammonium sulfate, \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) f. lead(II) nitrate, \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2},\) and barium chloride, \(\mathrm{BaCl}_{2}\)

Short answer

d. hydrofluoric acid, \(\mathrm{HF}\), and potassium sulfate, \(\mathrm{K}_{2} \mathrm{SO}_{4}\) No reaction occurs, as all products remain soluble. e. calcium chloride, \(\mathrm{CaCl}_{2}\), and ammonium sulfate, \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) No reaction occurs, as all products remain soluble. f. lead(II) nitrate, \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\), and barium chloride, \(\mathrm{BaCl}_{2}\) The net ionic equation is: \(\mathrm{Pb^{2+}(aq) + 2Cl^{-}(aq) \rightarrow PbCl_{2}(s)}\).

Step-by-step solution

Write down the chemical formulas

We have the given reactants: \(\mathrm{AgNO}_{3}(aq)\) and \(\mathrm{KCl}(aq)\).

Predict the products

Using solubility rules, we can predict the products: \(\mathrm{AgCl(s)}\) and \(\mathrm{KNO}_{3}(aq)\).

Balance the chemical equation

The balanced chemical equation is: \(\mathrm{AgNO}_{3}(aq) + \mathrm{KCl}(aq) \rightarrow \mathrm{AgCl(s)} + \mathrm{KNO}_{3}(aq)\).

Write the total ionic equation

The total ionic equation is: \(\mathrm{Ag^{+}(aq) + NO_{3}^{-}(aq) + K^{+}(aq) + Cl^{-}(aq) \rightarrow AgCl(s) + K^{+}(aq) + NO_{3}^{-}(aq)}\).

Write the net ionic equation

Cancel spectator ions and write the net ionic equation: \(\mathrm{Ag^{+}(aq) + Cl^{-}(aq) \rightarrow AgCl(s)}\). b. nickel(II) sulfate, \(\mathrm{NiSO}_{4}\), and barium chloride, \(\mathrm{BaCl}_{2}\)

Write down the chemical formulas

We have the given reactants: \(\mathrm{NiSO}_{4}(aq)\) and \(\mathrm{BaCl}_{2}(aq)\).

Predict the products

Using solubility rules, we can predict the products: \(\mathrm{NiCl}_{2}(aq)\) and \(\mathrm{BaSO}_{4}(s)\).

Balance the chemical equation

The balanced chemical equation is: \(\mathrm{NiSO}_{4}(aq) + \mathrm{BaCl}_{2}(aq) \rightarrow \mathrm{NiCl}_{2}(aq) + \mathrm{BaSO}_{4}(s)\).

Write the total ionic equation

The total ionic equation is: \(\mathrm{Ni^{2+}(aq) + SO_{4}^{2-}(aq) + Ba^{2+}(aq) + 2Cl^{-}(aq) \rightarrow Ni^{2+}(aq) + 2Cl^{-}(aq) + BaSO_{4}(s)}\).

Write the net ionic equation

Cancel spectator ions and write the net ionic equation: \(\mathrm{Ba^{2+}(aq) + SO_{4}^{2-}(aq) \rightarrow BaSO_{4}(s)}\). c. ammonium phosphate, \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}\), and calcium chloride, \(\mathrm{CaCl}_{2}\)

Write down the chemical formulas

We have the given reactants: \((\mathrm{NH}_{4})_{3}\mathrm{PO}_{4}(aq)\) and \(\mathrm{CaCl}_{2}(aq)\).

Predict the products

Using solubility rules, we can predict the products: \(3\mathrm{NH}_{4}\mathrm{Cl}(aq)\) and \(\mathrm{Ca_{3}(PO_{4})_{2}(s)}\).

Balance the chemical equation

The balanced chemical equation is: \((\mathrm{NH}_{4})_{3}\mathrm{PO}_{4}(aq) + 3\mathrm{CaCl}_{2}(aq) \rightarrow 6\mathrm{NH}_{4}\mathrm{Cl}(aq) + \mathrm{Ca_{3}(PO_{4})_{2}(s)}\).

Write the total ionic equation

The total ionic equation is: \(3\mathrm{NH}_{4}^{+}(aq) + \mathrm{PO}_{4}^{3-}(aq) + 3\mathrm{Ca^{2+}}(aq) + 6\mathrm{Cl^{-}}(aq) \rightarrow 6\mathrm{NH}_{4}^{+}(aq) + 6\mathrm{Cl^{-}}(aq) + \mathrm{Ca_{3}(PO_{4})_{2}(s)}\).

Write the net ionic equation

Cancel spectator ions and write the net ionic equation: \(3\mathrm{Ca^{2+}}(aq) + 2\mathrm{PO}_{4}^{3-}(aq) \rightarrow \mathrm{Ca_{3}(PO_{4})_{2}(s)}\)

Key concepts

Solubility Rules

The solubility rules are critical guidelines that predict whether a compound is soluble or insoluble in water. These rules are based on empirical observations and help determine the outcome of chemical reactions in aqueous solutions.

Some of the basic rules include:

• Most salts containing alkali metal ions (Li+, Na+, K+, Cs+, Rb+) and the ammonium ion (NH4+) are soluble.
• Nitrates (NO3-), bicarbonates (HCO3-), and chlorates (ClO3-) are generally soluble.
• Chlorides (Cl-), bromides (Br-), and iodides (I-) are soluble, with the exception of those formed with silver (Ag+), lead (II) (Pb2+), and mercury (II) (Hg2+).
• Sulfates (SO42-) are soluble except for those of calcium (Ca2+), strontium (Sr2+), barium (Ba2+), and lead (II) (Pb2+).
• Most hydroxides (OH-) and sulfides (S2-) are insoluble except for those of alkali metals and calcium, strontium, and barium to a lesser degree.
• Most phosphates (PO43-), carbonates (CO32-), chromates (CrO42-), and oxides (O2-) are insoluble except for their alkali metal compounds.

When applying these rules to the textbook exercises, one can predict that silver chloride (AgCl) will be insoluble and form a precipitate when silver nitrate (AgNO3) and potassium chloride (KCl) are mixed in aqueous solution. Similarly, barium sulfate (BaSO4) will precipitate when nickel(II) sulfate (NiSO4) and barium chloride (BaCl2) are mixed due to the low solubility of BaSO4.

Understanding these rules is fundamental in writing net ionic equations because they allow us to identify the formation of precipitates which are key components of the net ionic equation.

Balancing Chemical Equations

Balancing chemical equations is a crucial step in the study of chemistry. The law of conservation of mass dictates that matter is neither created nor destroyed in a chemical reaction. As such, in a balanced equation, the number of atoms of each element must be the same on both the reactant and product sides of the equation.

To balance an equation, one must use coefficients to adjust the number of molecules so that the atoms are equal on both sides. Steps typically involve:

• Writing down the correct formulas for all reactants and products.
• Counting the number of atoms of each element present on both sides of the equation.
• Adding coefficients to balance the atoms, starting with the most complex substance.
• Repeating the process until all elements are balanced.
• Checking to ensure that all coefficients are in the lowest possible ratio.

For example, in exercise (c) involving ammonium phosphate and calcium chloride, to balance the chemical equation, we adjust the coefficients to ensure that there are equal numbers of each type of ion on both sides. This yields six ammonium ions (NH4+) and six chloride ions (Cl-) on both sides of the equation, which also aligns with the produced calcium phosphate precipitate (Ca3(PO4)2).

The ability to balance chemical equations is essential for predicting the amounts of products and reactants in a given reaction and is foundational for further steps such as writing total and net ionic equations.

Spectator Ions

Spectator ions are ions that do not participate in the actual chemical reaction in an ionic equation. They appear unchanged on both the reactant and product sides of the equation and therefore do not affect the reaction outcome.

In the process of writing net ionic equations, the first step is to pen down the total ionic equation where all strong electrolytes (soluble compounds) are represented as their constituent ions. The next step is to identify and remove the spectator ions from both sides of the total ionic equation. This simplifies the equation to show only those species that are directly involved in the reaction, which represents the net ionic equation.

For instance, in the silver nitrate and potassium chloride reaction, the potassium ion (K+) and the nitrate ion (NO3-) are found unchanged on both sides of the equation. Since they don't change during the course of the reaction, they are spectator ions and are omitted in the net ionic equation, leaving us with the essence of the chemical change: \(\mathrm{Ag^{+}(aq) + Cl^{-}(aq) \rightarrow AgCl(s)}\).

Identifying spectator ions is not just an academic exercise; understanding their role (or lack thereof) in reactions is important. It helps in simplifying complex reactions to their fundamental components and can be particularly important in understanding processes in analytical chemistry and in industries where controlling chemical processes is crucial.