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01 Free Studying Resources 05 Secondary 3 Chemistry

Chapter 10: Metals

Secondary 3 Chapter 10: Metals

Question 1

The following observations were made when nickel and iron were placed separately into solutions of metals S, T and U.

The diagram below shows how the cross method is done to find the formula of ionic compounds.

Metal Salt solution of S Salt solution of T Salt solution of U
Nickel S displaced no reaction no reaction
Iron S displaced T displaced no reaction
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What is the correct order in increasing reactivity of the five metals?

A       S < Ni < Fe < T < U

B       S < Ni < T < Fe < U

C       U < Fe < T < Ni < S

D       U < T < Fe < Ni < S


U cannot be displaced by Nickel or Iron, thus U is the most reactive metal. It has to appear last in the sequence as the question is asking for increasing order of reactivity, from the least reactive metal to the most reactive metal. Options C and D are eliminated.

S was displaced from its salt solution by Nickel and Iron, meaning it is the least reactive metal. It should appear first in the answer.

T was only displaced by Iron but not nickel. This means that Iron is more reactive than T, which in turn is more reactive than Nickel.

Thus the order of reactivity in increasing order (least to most reactive) will be S, Ni, T, Fe, U.

Answer is B.

Question 2

Samples of solid magnesium carbonate were placed in crucibles X and Y.

Crucible X was heated strongly until there was no further change in mass while crucible Y was not heated.

Dilute hydrochloric acid was then added to both crucibles.

Which of the following describes the observations in crucibles X and Y?

A effervescence effervescence
B effervescence no effervescence
C no effervescence effervescence
D no effervescence no effervescence


Crucible X: When heated, magnesium carbonate will decompose to form magnesium oxide and carbon dioxide. Since it was heated until “there was no further change in mass”, this means that all magnesium carbonate has decomposed and the residue in the crucible is magnesium oxide.

MgCO₃ → MgO + CO₂

When dilute hydrochloric acid is added, there will be no effervescence, because no gaseous products are formed.

MgO + 2HCl → MgCl₂ + H₂O

Crucible Y: When dilute hydrochloric acid is added to magnesium carbonate, magnesium chloride, water and carbon dioxide gas is formed. Hence, effervescence will be observed.

MgCO₃ + 2HCl → MgCl₂ + H₂O +CO₂

Answer is C.

Question 3

Element X occurs naturally as the uncombined metal; element Y is obtained by chemical reduction of its oxide with carbon; element Z is obtained by electrolysing its molten chloride.

What is the order of reactivity of X, Y and Z?

Least reactive → Most Reactive
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Since element X occurs naturally, it is the least reactive metal.

Since element Z is obtained by electrolysis of molten chloride, Z is the most reactive metal.

Thus, the metals arranged in increasing reactivity is X < Y < Z.

Answer is A.