Science · Chemical substances · chapter 3 of 13

Class 10 Science Chapter 3: Metals and Non-metals case study question with answers

One case-based question of the kind the board asks in Section E: a passage and a table, then 3 parts worth 4 marks in all, with the answer and the marking scheme for each. Written from the NCERT chapter.

Case study · 4 marks

A science club in Bhopal is given four unlabelled metals, W, X, Y and Z, known to be sodium, magnesium, iron and copper in some order. Small pieces of each are tested with cold water, hot water, dilute hydrochloric acid and copper(II) sulphate solution. Their notes are in the table. A dash means the test was not done because the metal had already reacted with cold water.

Metal	Cold water	Hot water	Dilute HCl	CuSO₄ solution
W	reacts violently, gas catches fire	–	–	–
X	no change	bubbles, metal floats	brisk bubbles	blue colour fades, brown deposit
Y	no change	no change	slow bubbles	blue turns pale green, brown deposit
Z	no change	no change	no change	no change

Part 1 · 1 mark

The order of reactivity of the four metals, most reactive first, is

(a) W > X > Y > Z(b) W > Y > X > Z(c) X > W > Y > Z(d) Z > Y > X > W

Show answer

Answer: (a) W > X > Y > Z

W reacts even with cold water; X needs hot water; Y reacts only with the acid; Z reacts with nothing. So W > X > Y > Z.

Part 2 · 1 mark

Identify metal Z and give one reason from the table.

Answer and marking scheme

Z is copper: it does not react with dilute HCl, since it lies below hydrogen, and it cannot displace copper from copper sulphate.

copper, with a reason from the table (1)

Part 3 · 2 marks

Metal Y turns the blue solution pale green. Name Y and write the equation for the change.

Answer and marking scheme

Y is iron. Iron is more reactive than copper and displaces it: Fe + CuSO₄ → FeSO₄ + Cu. The pale green colour is iron(II) sulphate; the brown deposit is copper.

Y is iron (1)
Fe + CuSO₄ → FeSO₄ + Cu (1)

Name metal X, and explain why it floats in hot water and what it forms there.

Answer and marking scheme

X is magnesium. It does not react with cold water but reacts with hot water to form magnesium hydroxide and hydrogen; bubbles of hydrogen stick to its surface, so it floats.

X is magnesium (1)
forms Mg(OH)₂ and H₂; hydrogen bubbles make it float (1)

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