The treatment of galena with HNO3 produces a gas that is
(A) paramagnetic
(B) bent in geometry
(C) a

Q: Why doesn't the reaction produce $H_2S$ gas?

Nitric acid is a strong oxidizing agent. Instead of simply displacing the sulfide to form $H_2S$, it oxidizes the sulfide ion ($S^{2-}$) to elemental sulfur ($S$) and gets reduced itself to $NO$ or $NO_2$.

Q: How do we know if NO is acidic, basic, or neutral?

Non-metal oxides are generally acidic, but there are three classic exceptions you must memorize: $CO$, $NO$, and $N_2O$. These three are neutral oxides.

Q: Why is NO paramagnetic?

Paramagnetism arises from unpaired electrons. Nitrogen has 5 valence electrons and oxygen has 6, totaling 11. An odd number of electrons guarantees at least one unpaired electron, making the molecule paramagnetic.

Q: Can a diatomic molecule ever be bent?

No. A molecule with only two atoms only has one bond connecting them. Geometrically, two points always define a straight line, so all diatomic molecules are strictly linear.

Q: Is NO always colorless?

Yes, pure $NO$ gas is colorless. However, in an open test tube, it immediately reacts with atmospheric oxygen to form $NO_2$, which is a reddish-brown gas. This can sometimes cause confusion in lab observations!

Question

The treatment of galena with $	ext{HNO}_3$ produces a gas that is

Options:

(A) paramagnetic

(B) bent in geometry

(C) an acidic oxide

(D) colorless

Sigma Percentile · Accepted Answer

### The Setup: Galena Meets Nitric Acid

Imagine you are in a chemistry lab, holding a piece of **Galena**, which is the primary ore of lead, chemically known as lead(II) sulfide ($	ext{PbS}$).

You drop this dark, metallic-looking mineral into a test tube containing dilute nitric acid ($	ext{HNO}_3$).

Immediately, a vigorous reaction begins. Nitric acid is a notoriously strong oxidizing agent. It doesn't just dissolve the ore; it actively tears electrons away from the sulfide ions.

### The Master Equation

Let's look at the exact chemical equation governing this redox process:

$$ 3	ext{PbS} + 8	ext{HNO}_3 ightarrow 3	ext{Pb(NO}_3)_2 + 2	ext{NO} \uparrow + 4	ext{H}_2	ext{O} + 3	ext{S} \downarrow $$

In this reaction, the sulfide ion ($	ext{S}^{2-}$) is oxidized to elemental sulfur ($	ext{S}$), which often appears as a pale yellow precipitate.

Simultaneously, the nitrogen in nitric acid is reduced from a $+5$ oxidation state down to a $+2$ oxidation state.

This reduction produces a gas that bubbles out of the solution: **Nitric Oxide ($	ext{NO}$)**.

### Analyzing the Gas: Nitric Oxide

Now that we have identified the gas as $	ext{NO}$, we need to evaluate its physical and chemical properties to answer the question.

**1. Magnetic Nature:**
To determine if a molecule is paramagnetic or diamagnetic, we count its valence electrons. Nitrogen brings $5$ valence electrons, and oxygen brings $6$.

This gives us a total of $11$ valence electrons. Because $11$ is an odd number, it is mathematically impossible to pair all the electrons up.

There must be at least one unpaired electron. Any molecule with an unpaired electron is strictly **paramagnetic**.

**2. Molecular Geometry:**
What about its shape? $	ext{NO}$ is a diatomic molecule, meaning it consists of exactly two atoms.

Geometrically, the shortest distance between two points is a straight line. Therefore, any diatomic molecule must have a perfectly **linear** geometry. It is impossible for it to be bent.

**3. Chemical Nature and Color:**
In inorganic chemistry, non-metal oxides are typically acidic. However, there are three classic exceptions that you must memorize: $	ext{CO}$, $	ext{NO}$, and $	ext{N}_2	ext{O}$.

These three are **neutral oxides**. They do not form acids when dissolved in water.

Finally, pure $	ext{NO}$ gas is completely **colorless**.

*(Note: If you perform this in an open lab, the colorless $	ext{NO}$ will immediately react with oxygen in the air to form $	ext{NO}_2$, which is a reddish-brown gas. But the $	ext{NO}$ itself is colorless!)*

### Final Conclusion

Bringing all our observations together: the gas produced is $	ext{NO}$.

It is **paramagnetic** due to its odd number of electrons, and it is a **colorless** gas.

Therefore, the correct statements are that the gas is paramagnetic and colorless.

Animated Solution for Chemistry - s and p-Block Elements: The treatment of galena with $HNO_{3}$ produces a gas that is

Select Answer:

Visualized Solution

$Reaction of PbS and HNO_{3}$

$Chemical Equation$

$Magnetic Nature of NO$

$Geometry of NO$

$Nature and Color$

$Conclusion$

The Sigma Insight: Group 15 Elements

The Setup

The Master Equation

Analyzing the Gas

Final Conclusion

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Animated Solution for Chemistry - s and p-Block Elements: .math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } The treatment of galena with HNO3​ produces a gas that is