17.Unbalanced and incomplete chemical equations are given. Fill up the gaps by selecting from the formulae of the molecules given in brackets. Also balance the given equations. a) Zn + 2HCl → --a-- + H 2 b) 2Mg + --b-- → 2MgO c) 4Al +3O 2 → c

a) ZnCl₂; Zn + 2HCl ⟶ ZnCl₂ + H₂

b) MgO;  2Mg + O₂ ⟶ 2MgO

c) Al₂O₃; 4Al + 3O₂ ⟶ 2Al₂O₃

Explanation:

a) Zn + HCl

(i) Identify the missing compound

Zn + HCl ⟶ a +H₂

We have Zn and Cl on the left but not on the right.

a = ZnCl₂

(ii) Write the balanced equation

Zn + 2HCl ⟶ ZnCl₂ + H₂

b) 2Mg

(i) Identify the missing element

2Mg + b ⟶ 2MgO

We have O on the right but not on the left.

b = O₂

(ii) Write the balanced equation

2Mg + O₂ ⟶ 2MgO

c) 4Al + 3O₂

(i) Identify the missing compound

4Al + 3O₂ ⟶ c

We have Al and O on the left but not on the right.

The missing substance must be a compound of Al and O₂.

c = Al₂O₃

(ii) Write the balanced equation

4Al + 3O₂ ⟶ 2Al₂O₃

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