(a) Give three differences between electrovalent... | WAEC SSCE - Chemistry - 1991

Question 1 Report

(a) Give three differences between electrovalent compounds and covalent compounds

(b) List two physical properties of metals which can be accounted for by their structure

\(^{234}_{90}Th \to X + ^{234}_{91}Pa\)

(i) State the type of process involved in the reaction

(ii) Balance the equation equation and hence identify X.

(iii) Name one equipment which can be used to detect X.

(iv) Sketch a curveto show the mass of given quantity of thorium will change over a long period of time.

(d) Y is a moderately reactive divalent found naturally in the combined state as the trioxocarbonate (IV) salt, YCO\(_3\) is decomposed by strong heat, state the steps you would use in extracting Y from the ore. Write equation to show the chemical processes involved.

Answer

(a) Differences between electrovalent and covalent compounds

Electrovalent (ionic) compounds	Covalent compounds
They consist of oppositely charged ions held by strong electrostatic forces.	They consist of molecules formed by sharing electrons.
They conduct electricity when molten or in aqueous solution because their ions are mobile.	They generally do not conduct electricity because they have no mobile ions or electrons.
They are generally soluble in water and have high melting and boiling points.	They are generally insoluble in water, soluble in organic solvents, and have relatively low melting and boiling points.

(b)

Metals are good conductors of electricity because they contain mobile, delocalised electrons.
Metals are malleable and ductile because layers of positive metal ions can slide over one another while metallic bonding is maintained.

(c)

(i) The process is radioactive beta decay, involving emission of a beta particle.

(ii) The mass number is unchanged, while the atomic number increases from 90 to 91. Therefore,

\[{}^{234}_{90}\mathrm{Th}\ \longrightarrow\ {}^{0}_{-1}\mathrm{e}+{}^{234}_{91}\mathrm{Pa}\]

Thus, \(X\) is a beta particle, \({}^{0}_{-1}\mathrm{e}\).

(iii) A Geiger-Müller tube or Geiger-Müller counter can be used to detect the beta radiation.

(iv) The mass of thorium decreases exponentially with time, becoming half of its previous value in each successive half-life.

graph — Mass of a given quantity of thorium against time. The curve approaches zero but does not meet the time axis.

(d)

Crush and concentrate the carbonate ore, \(\mathrm{YCO_3}\).
Heat the concentrated ore strongly (calcination) to decompose the carbonate to the oxide:
\[\mathrm{YCO_3(s)\ \xrightarrow{\Delta}\ YO(s)+CO_2(g)}\]
Reduce the oxide with carbon in a furnace to obtain the metal:
\[\mathrm{YO(s)+C(s)\ \xrightarrow{\Delta}\ Y(s)+CO(g)}\]
Tap off the metal and purify it where necessary.

Read lesson note on Acids, Bases And Salts (JAMB)

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