Which one of the following nitrates will leave behind a metal on strong heating?
(a) Ferric nitrate

Q: Why doesn't Copper nitrate give Copper metal?

Copper is placed above Mercury in the reactivity series. Its oxide, CuO, is thermally stable and does not decompose further into the metal upon heating.

Q: What happens to alkali metal nitrates like $NaNO_3$ on heating?

Alkali metal nitrates decompose to give their corresponding nitrites and oxygen gas, not oxides or metals. For example, $2NaNO_3 \xrightarrow{\Delta} 2NaNO_2 + O_2$.

Q: Is $Ag_2O$ formed at all during the heating of $AgNO_3$?

Yes, $Ag_2O$ is formed as an intermediate product. However, because it is thermally unstable at the high temperatures used for decomposition, it immediately breaks down into Silver metal and Oxygen.

Q: What is the brown gas evolved during this reaction?

The brown gas is Nitrogen dioxide ($NO_2$). It is a common byproduct of the thermal decomposition of heavy metal nitrates.

Q: Can we get Gold metal by heating Gold nitrate?

Yes! Gold is located even lower than Silver in the reactivity series. Its compounds are highly unstable thermally, so heating Gold nitrate would readily leave behind pure Gold metal.

Question

Which one of the following nitrates will leave behind a metal on strong heating?

Options:

(A) Ferric nitrate

(B) Copper nitrate

(C) Manganese nitrate

(D) Silver nitrate

Sigma Percentile · Accepted Answer

Imagine you are in a chemistry lab, holding a test tube filled with a metal nitrate salt. You place it over a roaring Bunsen burner. What happens next? For most heavy metals, the heat tears the nitrate apart, leaving behind a solid metal oxide while releasing toxic brown nitrogen dioxide gas and oxygen.

But the question asks for something special: which nitrate leaves behind a **pure metal**, not an oxide? To answer this, we must consult the ultimate cheat sheet of chemistry—the **Electrochemical Series**.

### The General Rule of Decomposition

When we heat a typical heavy metal nitrate, the thermal energy breaks the bonds, leading to decomposition. The general reaction looks like this:

$$2M(NO_3)_2 \xrightarrow{\Delta} 2MO + 4NO_2 + O_2$$

The solid residue left behind is the metal oxide ($MO$). For many metals, this oxide is incredibly stable and will happily sit in the test tube no matter how much you heat it.

### The Reactivity Series and Thermal Stability

Here is where the magic happens. The stability of a metal oxide is directly linked to the metal's position in the reactivity series. Metals that are highly reactive form very strong bonds with oxygen.

However, there is a critical boundary in the series: **Mercury (Hg)**.

Metals that lie *below* Mercury (such as Silver, Platinum, and Gold) are so unreactive that their hold on oxygen is extremely weak. Their oxides are **thermally unstable**. If you try to heat them, they simply give up and release the oxygen, leaving behind the pure metal.

$$2MO \xrightarrow{\Delta} 2M + O_2$$

### Analyzing the Options

Let's look at the candidates provided in the question: Manganese (Mn), Iron (Fe), Copper (Cu), and Silver (Ag).

If we check their positions in the reactivity series, Manganese, Iron, and Copper are all placed comfortably *above* Mercury. This means their oxides ($MnO_2$, $Fe_2O_3$, and $CuO$) are thermally stable. Heating their nitrates will only yield these oxides, not the pure metals.

### The Special Case of Silver

Silver (Ag), on the other hand, is a noble metal sitting below Mercury. When we subject Silver nitrate ($AgNO_3$) to strong heating, it initially tries to form Silver oxide ($Ag_2O$).

$$2AgNO_3 \xrightarrow{\Delta} Ag_2O + 2NO_2 + \frac{1}{2}O_2$$

But the intense heat is too much for the fragile Silver-Oxygen bonds. The Silver oxide immediately undergoes secondary decomposition:

$$Ag_2O \xrightarrow{\Delta} 2Ag + \frac{1}{2}O_2$$

Combining these steps, the overall reaction beautifully yields pure Silver metal:

$$2AgNO_3 \xrightarrow{\Delta} 2Ag + 2NO_2 + O_2$$

And there you have it! The shiny, metallic residue left in your test tube is pure silver. Therefore, Silver nitrate is the correct answer.

Animated Solution for Chemistry - d and f-Block Elements: Which one of the following nitrates will leave behind a metal on strong heating?

Select Answer:

Visualized Solution

$M (N O_{3})_{x} Δ M + \dots$

$2 M (N O_{3})_{2} Δ 2 M O + 4 N O_{2} + O_{2}$

$M O Δ M + \frac{1}{2} O_{2} (i f M < H g)$

$M n, F e, C u > H g$

$2 A g N O_{3} Δ 2 A g + 2 N O_{2} + O_{2}$

$A g N O_{3}$

The Sigma Insight: d-block Elements

The General Rule of Decomposition

The Reactivity Series and Thermal Stability

Analyzing the Options

The Special Case of Silver

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