Chemistry
Give reasons for the following:
(a) Electronegativity increases across a Period from left to right in the Modern periodic table
(b) Aluminium and zinc powder cannot be distinguished by strong alkalis.
(c) Water is not added to sulphuric acid to dilute it.
Periodic Table
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Answer
(a) Across a period the nuclear (effective) charge on the atoms increases while the number of electron shells remains the same. As a result, atomic radius decreases and the attraction of the nucleus for the bonding electrons becomes stronger, so electronegativity increases from left to right.
(b) When treated with a strong alkali (like sodium hydroxide, NaOH), both aluminium and zinc powder dissolve and form soluble complex salts with the evolution of hydrogen gas. As both metals behave in the same way, the alkali test cannot distinguish between them.
(c) Water is never poured on acid to dilute it as large amount of heat is evolved which changes poured water to steam. The steam so formed causes spurting of acid which can cause burn injuries.
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