Question

Predict the products and write a balanced molecular equation for each reaction. If no reaction occurs, write "NO REACTION." a. \(\mathrm{HCl}(a q)+\mathrm{Hg}_{2}\left(\mathrm{NO}_{3}\right)_{2}(a q) \longrightarrow\) b. \(\mathrm{KHSO}_{3}(a q)+\mathrm{HNO}_{3}(a q) \longrightarrow\) c. aqueous ammonium chloride and aqueous lead(II) nitrate d. aqueous ammonium chloride and aqueous calcium hydroxide

Short answer

a. 2 HCl(aq) + Hg2(NO3)2(aq) -> Hg2Cl2(s) + 2 HNO3(aq); b. KHSO3(aq) + HNO3(aq) -> KNO3(aq) + H2SO4(aq); c. NO REACTION; d. 2 NH4Cl(aq) + Ca(OH)2(aq) -> CaCl2(aq) + 2 H2O(l) + 2 NH3(g).

Step-by-step solution

Predicting the products for reaction a

For the reaction between hydrochloric acid (HCl) and mercury(I) nitrate (Hg2(NO3)2), the HCl will donate a proton (H+) to one of the nitrates, forming nitric acid (HNO3) and solid mercury(I) chloride (Hg2Cl2), since mercury(I) chloride is insoluble in water.

Writing the balanced equation for reaction a

Balance the molecular equation by ensuring there are equal numbers of each type of atom on both sides of the reaction. The balanced equation is 2 HCl(aq) + Hg2(NO3)2(aq) -> Hg2Cl2(s) + 2 HNO3(aq).

Predicting the products for reaction b

When potassium bisulfite (KHSO3) reacts with nitric acid (HNO3), the H+ ion from HNO3 will react with the bisulfite ion (HSO3-) to form sulfuric acid (H2SO4) and nitrate ion (NO3-). Potassium will pair with nitrate to form potassium nitrate (KNO3).

Writing the balanced equation for reaction b

The molecular equation for the reaction between KHSO3 and HNO3 needs to be balanced. The balanced equation is KHSO3(aq) + HNO3(aq) -> KNO3(aq) + H2SO4(aq).

Predicting the products for reaction c

The reaction between ammonium chloride (NH4Cl) and lead(II) nitrate (Pb(NO3)2) involves a double-replacement reaction where the ions in the reactants switch places. Ammonium will pair with nitrate, and lead(II) will pair with chloride. However, all products formed are soluble in water; hence no solid precipitate forms, indicating no visible chemical reaction.

Confirming no reaction for reaction c

Since all products in the reaction are soluble and no gas or solid forms, we can denote this as 'NO REACTION'.

Predicting the products for reaction d

The reaction between ammonium chloride (NH4Cl) and calcium hydroxide (Ca(OH)2) will form calcium chloride (CaCl2), water (H2O), and ammonia (NH3). Ammonia is a gas at room temperature and thus will leave the solution.

Writing the balanced equation for reaction d

Balancing the reaction will yield 2 NH4Cl(aq) + Ca(OH)2(aq) -> CaCl2(aq) + 2 H2O(l) + 2 NH3(g). We can verify this is balanced by counting the atoms of each element on both sides of the equation.

Key concepts

Chemical Reaction Prediction

Predicting the outcome of a chemical reaction is crucial for understanding how substances interact to create new products. This process involves identifying the reactants, their states (solid, liquid, gas, aqueous), and how they will combine based on certain rules of chemistry.

For example, when acids and bases react, they typically form salt and water, as seen in neutralization reactions. Metal carbonates and acids generally produce carbon dioxide, water, and a salt. By identifying the type of reactants, one can often predict the type of reaction and its products.

The products of a reaction are determined by the reactivity of the elements or compounds and the rules governing their interactions, such as solubility rules and activity series. Predicting a reaction often means identifying the possible ionic compounds that could form and determining whether any of these are insoluble in water or might decompose, release gas, or in some other way show a chemical change has occurred.

Double-Replacement Reaction

A double-replacement reaction, also known as a metathesis reaction, occurs when parts of two ionic compounds are exchanged and form two new compounds. This type of reaction is represented by the general formula: \[ AB + CD \rightarrow AD + CB \]

In double-replacement reactions, the cations (positively charged ions) and anions (negatively charged ions) of the reacting compounds swap partners. To predict the outcome of such reactions, one must use solubility rules to assess whether any of the new combinations result in the formation of a precipitate, a gas, or a weakly dissociating compound like water.

An example of a double-replacement reaction is found in step 7's description of the reaction between ammonium chloride and calcium hydroxide. When these compounds react, they exchange ions and produce calcium chloride, water, and ammonia, showing a typical behavior of such reactions.

Precipitation Reaction

Precipitation reactions are a type of chemical reaction where a solid, known as a precipitate, is formed from the reaction of two solutions containing soluble salts. The precipitate is an insoluble compound that emerges from the reaction and can often be observed as a cloudy or solid substance appearing in the previously clear solution.

Precipitation is typically the result of a double-replacement reaction when the newly formed product is insoluble. Solubility rules help predict whether a certain product will precipitate given the reactants’ ionic constituents.

For example, in step 1 of our exercise, the reaction between hydrochloric acid and mercury(I) nitrate leads to the formation of solid mercury(I) chloride and nitric acid. The mercury(I) chloride is insoluble in water and thus precipitates, which is an indicator that a chemical reaction has occurred. Knowing the solubility rules aids in predicting which combinations of ions will produce a precipitate and can help confirm the completion of the reaction.