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secondary 4 | Chemistry
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Can someone tell me how to do qn 4 and explain to me why answer for qn 5 part b is Q and S?
Recycling of metals is simply about renewing used metals which may have been discarded rather than mining the same quantity of metal.
Copper is considered relatively unreactive when compared to other metals. For this reason, it is relatively easy to purify copper to obtain pure copper once again, which in technicality is no different from pure mined copper.
An obvious advantage of recycling copper is reducing metal waste which would otherwise occur, thus reducing the space needed to discard unwanted copper. This, in turn, leads to less mining of copper from natural sources since the demands for copper can be partly met by recycling.
A not-so-obvious advantage of recycling copper is energy savings (this is only more obvious to factories dealing with copper products). The total energy cost required to recycle copper is only a fractional proportion of the total energy cost required to mine the same quantity of copper.
You can do some further reading online on recycling of copper if you are interested.
Hydrogen is the reference barrier for the reaction (“passing mark”). I believe it is because acids, which provide the easiest conditions for reaction, contain lots of positive hydrogen ions.
Any metal which is lower than hydrogen in the reactivity series (“D7, E8, F9”) is relatively unreactive.
Thus, hydrogen should be placed between Q and S, because Q “barely passes the examination” whereas S “fails the examination”. Remember that hydrogen is the “passing mark”.
Usually metals above hydrogen in the reactivity series can react with acids such as hydrochloric acid by virtue of metal displacement (just as halogens would for displacement reactions).
Suppose you have magnesium metal placed in hydrochloric acid. The magnesium atoms will displace the hydrogen ions from the hydrochloric acid solution, thereby forming a compound magnesium chloride (though still in ion form in aqueous solution) and hydrogen gas (thanks to the displacement).
Of course, hydrogen gas does not react with hydrochloric acid because hydrogen does not displace hydrogen (all hydrogen atoms of a single isotope are treated to be identical to one another).
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