Table below shows the observation of an experiment to study the reactivity of metals X , Y and Z with oxygen. Metal powders of X , Y and Z are heated in a flow of oxygen. Potassium manganate(VII) powder is used as the source of oxygen.
Q : Based on the observation in the above table, arrange
the reactivity of metal X, Y and Z in ascending order.
A : X, Z, Y
Explanation :
The more vigorous the reaction the more reactive the metal. Vigorousness in a reaction indicates the reactivity of a substance. Vigorousness is determined through observation such as brightness of flame or glow, speed of the reaction, etc. For the above case, the brighter the flame the more reactive the metal. Thus, the higher its position in the Reactivity series of metals with oxygen.
In F4 and F5 Chemistry syllabus, the term reactivity is mainly used in
i) Determining empirical formula of metal oxide (F4 - Chap 3)
ii) Comparing reactivity of Group 1 elements (F4 – Chap 4)
iii) Comparing reactivity of Group 17 elements (F4 – Chap 4)
iv) Reaction between metals and oxygen, Reactivity
series (F5 – Chap 3)
v) Reaction between carbon / hydrogen with metal oxides (F5–Chap 3)
vi) Reaction between carbon dioxide / water with metal (F5–Chap 3)
vii) Extraction of metals (F5 – Chap 3)
ELECTROPOSITIVITY :
Diagram below shows the set up of apparatus of a chemical cell.
Q i) State the negative terminal
A : Magnesium
Q ii) Explain your answer in Q(i).
A : Magnesium is more electropositive than copper / Magnesium is
higher than copper in the electrochemical series
Explanation :
Metal that acts as a negative terminal must be a metal with higher tendency to donate electrons. Between magnesium and copper, magnesium loses electrons more easily than copper. So, magnesium is said more electropositive. The term reactivity is not suitable to be used here because the process of losing electrons in the chemical cell does not show any vigorousness.
In F4 and F5 Chemistry syllabus, the term reactivity is mainly used in
i) Comparing electropositivity of Group 1 elements (F4 – Chap 4)
ii) Comparing electropositivity of elements across a period
in the Periodic Table (F4 – Chap 4)
iii)Determining the negative terminal of a voltaic cell (F4 - Chap 6)
iv) Displacement of metal from its salt solution (F4 – Chap 6 & F5 – Chap 3)
ELECTRONEGATIVITY :
Table below shows three pairs of chemicals.
Q i) Put a tick (/) in the box beside the pair of chemicals which will
undergo a displacement reaction. Explain your answer.
A : Chlorine is more electronegative than iodine / Chlorine is higher
than iodine in the group 17
Explanation :
It goes the same with the term electronegativity. Electronegativity means a measurement of the strength of the atom of an element to attract electrons towards its nucleus. The atomic size of chlorine is smaller than iodine. Therefore the strength of the nucleus of chlorine to attract electrons is stronger than iodine. Thus, chlorine is said more electronegative than iodine. That is why chlorine is able to displace iodine from its halide solution.
In addition, the reaction also does not show any vigorousness, that is why the term reactivity is not suitable to be used to explain the reaction.
In F4 and F5 Chemistry syllabus, the term reactivity is mainly used in
i) Comparing electronegativity of Group 17 elements (F4 – Chap 4)
ii) Comparing electronegativity of elements across a period
in the Periodic Table (F4 – Chap 4)
iii)Displacement of halogen from its halide solution (F5 – Chap 3)
