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Question 13 Marks
Thin strips of magnesium, copper, and iron are taken.
Write down what happens when these metals are treated as follows:
    1. Heated in presence of air
    2. Heated with dil.HCl
    3. Added to an aqueous solution of zinc sulphate.
Answer
  1. On heating thin strips of magnesium, copper, and iron, they form oxides.
  2. Magnesium and iron react with HCl liberating hydrogen and forming their respective salts. Hydrogen cannot be prepared from metals that are below it in the activity series of metals (such as copper) because only metals that are more reactive than hydrogen can displace it from acids.
  3. Only magnesium will displace zinc from zinc sulphate solution because magnesium is more reactive than zinc in the activity series of metals. No reaction takes place in the case of copper and iron because they are less reactive than zinc.
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Question 23 Marks
Why zinc and aluminium are considered to have a unique nature. Give balanced equations to support your answer.
Answer
They react with acids and can even react with hot concentrated alkalis to form hydrogen and soluble salt.
$Zn + 2NaOH → Na_2ZnO_2+ H_2$
$2Al + 6NaOH→ 2Na_2Al O_3+ 3H_2$​​​​​​​
Oxides and hydroxides of zinc and aluminum are amphoteric. They react with both bases and acids to give salt and water.
$ZnO+ 2HCl → ZnCl_2+ H_2O$
$ZnO+ 2NaOH →Na_2ZnO_2+ H_2O$
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[3 Mark Question Answer] - CHEMISTRY STD 9 Questions - Vidyadip