Question

Write the molecular equation and the net ionic equation for the reaction of solid iron(II) sulfide and hydrochloric acid. Add phase labels.

Short answer

Molecular: FeS(s) + 2 HCl(aq) → H₂S(g) + FeCl₂(aq); Net ionic: FeS(s) + 2 H⁺(aq) → H₂S(g) + Fe²⁺(aq).

Step-by-step solution

Identify Reactants and Products

Iron(II) sulfide, FeS, is a solid, and hydrochloric acid, HCl, is aqueous. The reaction of FeS with HCl produces hydrogen sulfide, H\(_2\)S, gas and iron(II) chloride, FeCl\(_2\), which is aqueous.

Write the Molecular Equation

The molecular equation for the reaction is: \[ \text{FeS(s) + 2 HCl(aq) \rightarrow H}_2\text{S(g) + FeCl}_2\text{(aq)} \] where FeS(s) is solid iron(II) sulfide, HCl(aq) is hydrochloric acid, H\(_2\)S(g) is hydrogen sulfide gas, and FeCl\(_2\)(aq) is aqueous iron(II) chloride.

List All Ionic Species in Aqueous Solution

The ionic species in the reaction are identified. In this case, FeS is a solid and does not dissociate, while HCl dissociates into H\(^+\) and Cl\(^-\) ions. FeCl\(_2\) dissociates into Fe\(^{2+}\) and two Cl\(^-\) ions.

Write the Total Ionic Equation

The total ionic equation shows all the ions, including: \[ \text{FeS(s) + 2 H}^+(aq) + 2 \text{Cl}^-(aq) \rightarrow \text{H}_2\text{S(g) + Fe}^{2+}(aq) + 2 \text{Cl}^-(aq)} \] where the spectator ions are identified for removal.

Write the Net Ionic Equation

After removing spectator ions, which in this reaction are the 2Cl\(^-\) ions, the net ionic equation is: \[ \text{FeS(s) + 2 H}^+(aq) \rightarrow \text{H}_2\text{S(g) + Fe}^{2+}(aq)} \] which indicates the reacting ions and resulting products without spectator ions.

Key concepts

Molecular Equation

A molecular equation represents the chemicals involved in a reaction and their respective phases, without breaking them into ions.
In this representation, you highlight all reactants and products as whole compounds, showing the transformation process.
For example, in the equation of iron(II) sulfide and hydrochloric acid: \[\text{FeS(s) + 2 HCl(aq) \rightarrow H}_2\text{S(g) + FeCl}_2\text{(aq)}\]
FeS remains intact as a solid with 's,' HCl is aqueous with 'aq,' H\(_2\)S appears as a gas 'g,' and FeCl\(_2\) is aqueous 'aq.'

• "s" stands for solid
• "aq" for aqueous solutions
• "g" for gases

This equation provides a clear picture of the reaction process without detailing ionic participants.

Net Ionic Equation

A net ionic equation drills down to the essence of a chemical reaction, showcasing only the ions that participate in changing the state. We often remove spectator ions, which do not engage directly in the chemical change.
Using our example, the balanced net ionic equation becomes: \[\text{FeS(s) + 2 H}^+(aq) \rightarrow \text{H}_2\text{S(g) + Fe}^{2+}(aq)\]
Here, the chloride ions (Cl\(^-\)) are spectators and do not appear because they do not change during the reaction.
This approach simplifies the reaction to its core parts, helping to underline the actual chemical change happening in the system.
Remove ions like observers, zeroing in on what's impactful and different.

Stoichiometry

Stoichiometry focuses on quantitative relationships in reactions—how much of one thing reacts with how much of another.
It's the "bookkeeping" of chemistry, ensuring mass and charges balance according to the conservation laws.
Consider the molecular equation: \[\text{FeS(s) + 2 HCl(aq) \rightarrow H}_2\text{S(g) + FeCl}_2\text{(aq)}\]
We see that one mole of FeS reacts with two moles of HCl to produce one mole of H\(_2\)S and one mole of FeCl\(_2\).

• This ratio (1:2:1:1) is crucial for determining how much reactants you need and how much product to expect.
• It also ensures chemical consistency and predictability in reactions.

Stoichiometry ensures you're prepared—no surprises—by predicting outcomes with precision.

Phase Labels

Phase labels are critical in equations as they reveal the state of each substance involved: solid, liquid, gas, or aqueous.
These labels give insight on how substances physically situate during the reaction and influence the dynamics.
In our given equation, FeS is marked as ('s') for solid, HCl ('aq') for aqueous, H\(_2\)S ('g') for gas, and FeCl\(_2\) is also ('aq'), denoting aqueous. Phaser markers reveal:

• "s" for substances retaining a fixed shape and volume
• "g" indicating substances occupying all space available
• "aq" suggesting water is the dissolving medium
• "l" (liquid) when applicable, but not featured here

Understanding and using phase labels ensure that the physical aspects of a reaction are as clear as the chemical intricacies.