A laboratory technician reacts separate samples of two copper-based alloys, X and Y, with … — JAMB UTME

A laboratory technician reacts separate samples of two copper-based alloys, $X$ and $Y$ , with excess concentrated trioxonitrate(V) acid ( $HNO_3$ ). Sample $X$ dissolves completely to yield a clear blue solution with no residue, whereas Sample $Y$ yields a blue solution containing an insoluble white solid. Which of the following correctly identifies Alloys $X$ and $Y$ and the constituent element responsible for the insoluble white solid?

Alloy $X$ is brass, Alloy $Y$ is bronze, and tin forms the insoluble solid.Answer
B
Alloy $X$ is bronze, Alloy $Y$ is brass, and zinc forms the insoluble solid.
C
Alloy $X$ is brass, Alloy $Y$ is bronze, and copper forms the insoluble solid.
D
Alloy $X$ is duralumin, Alloy $Y$ is brass, and aluminium forms the insoluble solid.

Answer

Alloy

X

is brass, Alloy

Y

is bronze, and tin forms the insoluble solid.

Brass (

Cu + Zn

) dissolves completely in concentrated trioxonitrate(V) acid to produce soluble copper(II) trioxonitrate(V) and zinc trioxonitrate(V). Bronze (

Cu + Sn

) contains tin, which is oxidized by concentrated trioxonitrate(V) acid to form insoluble metastannic acid (

H_2SnO_3

), creating a white precipitate in the blue copper solution.

Step-by-Step Solution

Identify the elemental compositions of the copper alloys brass and bronze.

Brass is an alloy of copper (

Cu

) and zinc (

Zn

). Bronze is an alloy of copper (

Cu

) and tin (

Sn

Knowing constituent elements is essential to predict chemical reactions with concentrated acid.

Analyze the chemical reaction of Brass (Alloy

X

) with concentrated

HNO_3

Both

Cu

and

Zn

react to form soluble metal trioxonitrate(V) salts:

Cu(NO_3)_2

(blue) and

Zn(NO_3)_2

(colorless). The mixture forms a completely clear blue solution.

All nitrate salts of copper and zinc are soluble in aqueous media.

Analyze the chemical reaction of Bronze (Alloy

Y

) with concentrated

HNO_3

Copper dissolves to form soluble blue

Cu(NO_3)_2

, while tin (

Sn

) is oxidized by concentrated

HNO_3

to form hydrated tin(IV) oxide (

SnO_2 \cdot xH_2O

or metastannic acid,

H_2SnO_3

), which precipitates as an insoluble white solid.

Tin exhibits anomalous behavior with concentrated nitric acid compared to zinc, forming an insoluble oxide rather than a soluble nitrate salt.

Key Concept

Chemical differentiation of brass and bronze based on constituent metal reactivity with concentrated trioxonitrate(V) acid

Estimated Time:1m 30s

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