Problem 16 - Chemistry An Atoms First Approach

Question

Write equations showing the ions present after the following strong electrolytes are dissolved in water. a. \(\mathrm{HNO}_{3}\) b. \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) c. \(A I\left(N O_{3}\right)_{3}\) d. \(\operatorname{SrBr}_{2}\) e. \(\mathrm{KClO}_{4}\) f. \(\mathrm{NH}_{4} \mathrm{Br}\) g. \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) h. \(\mathrm{CuSO}_{4}\) i. \(\quad\) NaOH

Step-by-Step Solution

Answer

a. \(\mathrm{HNO_3} (aq) \rightarrow \mathrm{H^+} (aq) + \mathrm{NO_3^-} (aq)\) b. \(\mathrm{Na_2SO_4} (aq) \rightarrow 2\mathrm{Na^+} (aq) + \mathrm{SO_4^{2-}} (aq)\) c. \(Al(NO_3)_3 (aq) \rightarrow Al^{3+} (aq) + 3NO_3^- (aq)\) d. \(\mathrm{SrBr_2} (aq) \rightarrow \mathrm{Sr^{2+}} (aq) + 2\mathrm{Br^-} (aq)\) e. \(\mathrm{KClO_4} (aq) \rightarrow \mathrm{K^+} (aq) + \mathrm{ClO_4^-} (aq)\) f. \(\mathrm{NH_4Br} (aq) \rightarrow \mathrm{NH_4^+} (aq) + \mathrm{Br^-} (aq)\) g. \(\mathrm{NH_4NO_3} (aq) \rightarrow \mathrm{NH_4^+} (aq) + \mathrm{NO_3^-} (aq)\) h. \(\mathrm{CuSO_4} (aq) \rightarrow \mathrm{Cu^{2+}} (aq) + \mathrm{SO_4^{2-}} (aq)\) i. \(\mathrm{NaOH} (aq) \rightarrow \mathrm{Na^+} (aq) + \mathrm{OH^-} (aq)\)

Step 1: a. Dissociation of \(\mathrm{HNO}_{3}\)

HNO3 is a strong acid that dissociates completely in water as follows: \(\mathrm{HNO_3} (aq) \rightarrow \mathrm{H^+} (aq) + \mathrm{NO_3^-} (aq)\)

Step 2: b. Dissociation of \(\mathrm{Na}_{2} \mathrm{SO}_{4}\)

Na2SO4 is a salt that dissociates completely in water as follows: \(\mathrm{Na_2SO_4} (aq) \rightarrow 2\mathrm{Na^+} (aq) + \mathrm{SO_4^{2-}} (aq)\)

Step 3: c. Dissociation of \(Al\left(N O_{3}\right)_{3}\)

Al(NO3)3 is a salt that dissociates completely in water as follows: \(Al(NO_3)_3 (aq) \rightarrow Al^{3+} (aq) + 3NO_3^- (aq)\)

Step 4: d. Dissociation of \(\mathrm{SrBr_{2}}\)

SrBr2 is a salt that dissociates completely in water as follows: \(\mathrm{SrBr_2} (aq) \rightarrow \mathrm{Sr^{2+}} (aq) + 2\mathrm{Br^-} (aq)\)

Step 5: e. Dissociation of \(\mathrm{KClO_4}\)

KClO4 is a salt that dissociates completely in water as follows: \(\mathrm{KClO_4} (aq) \rightarrow \mathrm{K^+} (aq) + \mathrm{ClO_4^-} (aq)\)

Step 6: f. Dissociation of \(\mathrm{NH_4Br}\)

NH4Br is a salt that dissociates completely in water as follows: \(\mathrm{NH_4Br} (aq) \rightarrow \mathrm{NH_4^+} (aq) + \mathrm{Br^-} (aq)\)

Step 7: g. Dissociation of \(\mathrm{NH_4NO_3}\)

NH4NO3 is a salt that dissociates completely in water as follows: \(\mathrm{NH_4NO_3} (aq) \rightarrow \mathrm{NH_4^+} (aq) + \mathrm{NO_3^-} (aq)\)

Step 8: h. Dissociation of \(\mathrm{CuSO_4}\)

CuSO4 is a salt that dissociates completely in water as follows: \(\mathrm{CuSO_4} (aq) \rightarrow \mathrm{Cu^{2+}} (aq) + \mathrm{SO_4^{2-}} (aq)\)

Step 9: i. Dissociation of NaOH

NaOH is a strong base that dissociates completely in water as follows: \(\mathrm{NaOH} (aq) \rightarrow \mathrm{Na^+} (aq) + \mathrm{OH^-} (aq)\)

Key Concepts

Dissociation Equations

When a strong electrolyte is dissolved in water, it dissociates into its constituent ions. This process is represented by dissociation equations. For example, when nitric acid \(\mathrm{HNO_3}\) dissolves in water, it breaks down into \(\mathrm{H^+}\) and \(\mathrm{NO_3^-}\) ions. These equations help us understand what happens at the molecular level when a compound is dissolved.

• Strong acids like \(\mathrm{HNO_3}\) dissociate completely, releasing \(\mathrm{H^+}\) ions.
• Salts like \(\mathrm{Na_2SO_4}\) dissociate to yield cations and anions, here sodium ions \(2\mathrm{Na^+}\) and sulfate ions \(\mathrm{SO_4^{2-}}\).
• Bases like \(\mathrm{NaOH}\) dissociate to produce hydroxide ions \(\mathrm{OH^-}\).

A dissociation equation is essential for understanding the behavior of electrolytes in solution. It shows us how the original molecules separate into ions when they interact with water.

Ions in Solution

Ions in solution are the charged particles that result from the dissociation of strong electrolytes. When these ions are in a solution, they are surrounded by water molecules. This process is known as hydration.

• Cations such as sodium ions \(\mathrm{Na^+}\) are positively charged and are attracted to the negative oxygen end of water molecules.
• Anions such as nitrate ions \(\mathrm{NO_3^-}\) are negatively charged and are surrounded by the positive hydrogen ends of water molecules.
• The mobility of these ions is crucial for conducting electricity in the solution.

Each type of ion plays a unique role in chemical reactions and physical properties of the solution. Their presence impacts the solution's conductivity, reactivity, and overall behavior.

Acid-Base Chemistry

Acid-base chemistry revolves around the release and acceptance of protons \(\mathrm{H^+}\). When acids like \(\mathrm{HNO_3}\) dissolve in water, they release \(\mathrm{H^+}\) ions, which is a characteristic trait of acids. Conversely, bases like \(\mathrm{NaOH}\) release \(\mathrm{OH^-}\) ions.

• Acids are proton donors, evident in the dissociation of \(\mathrm{HNO_3}\) into \(\mathrm{H^+}\) and \(\mathrm{NO_3^-}\).
• Bases are proton acceptors or hydroxide ion donors, as \(\mathrm{NaOH}\) releases \(\mathrm{OH^-}\).
• The interaction of \(\mathrm{H^+}\) and \(\mathrm{OH^-}\) ions leads to the formation of water, essential in neutralization reactions.

The concepts of acidity and basicity help us understand the nature of substances and their reactions in aqueous solutions. They are pivotal in applications ranging from industrial processes to biological systems.

Solubility Rules

Solubility rules help determine whether a compound will dissociate when dissolved in water, indicating whether it is a strong or weak electrolyte. These rules are guidelines based on empirical observations.

• Nitrates, such as those in \(\mathrm{Al(NO_3)_3}\), are generally soluble in water.
• Most salts of alkali metals like sodium in \(\mathrm{Na_2SO_4}\) are soluble.
• Salts containing \(\mathrm{NH_4^+}\) ions, like \(\mathrm{NH_4NO_3}\), are usually soluble.
• Exceptions exist, particularly with compounds containing lead, mercury, and silver.

Understanding solubility rules allows predictions about a compound's behavior in water, affecting its use in reactions, synthesis, and separation processes.