Question

# (a) Compound X consists of molecules. Choose the letter corresponding to the correct answer from the choices (a), (b), (c) and (d) given below: (i) The type of bonding in X will be: (a) ionic (b) electrovalent (c) covalent (d) molecular (ii) X is likely to have a: (a) low melting point and high boiling point (b) high melting point and low boiling point (c) low melting point and low boiling point (d) high milting point and high boiling point (iii) In the liquid state, X will: (a) become ionic (b) be an electrolyte (c) conduct electricity (d) not conduct electricity (b) (i) Acids dissolve in water to produce positively charged ions. Draw the structure of these positive ions. (ii) Explain, why carbon tetrachloride does not dissolve in water? (iii) Elements Q and S react together to form an ionic compound. Under normal conditions, which physical state will the compound QS exist in? (iv) Can Q and S, both be metals? Justify your answer.

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Solution

## (a) (i) Compound X consists of molecules; so, it will contain covalent bonds. Hence, the correct answer is (c). (ii) X is covalent in nature; therefore, it will have low melting and boiling points. Hence, the correct answer is (c). (iii) In liquid state, X will not conduct electricity due to absence of free ions. Hence, the correct answer is (d). (b) (i) When acids are dissolved in water, they release H+ ions that combine with water molecules to form hydronium ion (H3O+). Its structure is given below: ${\left[\mathrm{H}-\underset{\overline{)}}{\overset{..}{\mathrm{O}}}-\mathrm{H}\phantom{\rule{0ex}{0ex}}\mathrm{H}\right]}^{+}\phantom{\rule{0ex}{0ex}}$ (ii) Carbon tetrachloride contains four polar covalent C − Cl bonds. These Polar bonds have direction. Direction of polar bond is represented by arrow pointing towards the more electronegative atom (C$\to$Cl). These four polar covalent bonds are present in opposite directions (as shown below), due to which the entire compound is considered as non-polar compound. On the other hand, water is a polar compound due to the presence of polar covalent O − H bonds along with two lone pair of electrons on oxygen atom. Non-polar compounds are insoluble in polar compounds; therefore, carbon tetrachloride does not dissolve in water. (iii) As QS is an ionic compound, it would be solid under normal conditions. (iv) Both Q and S cannot be metals because an ionic compound is formed by the combination of a metal (that loses electrons to form a cation) and a non-metal (that gains the electrons to form an anion).

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