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The physical states of the reactants and products can be represented by using the symbols (s) for solids, (l) for liquids, (g) for gases and (aq) for aqueous solution along with their respective formulae. The word aqueous is written if the reactant or product is present as a solution in water. Precipitate can also be represented by using an arrow pointing downwards (↓) instead of using symbol (s).
In the same way, the gaseous state of an evolved gas can be represented by using an arrow pointing upward in direction (↑) instead of using symbol (g). The specific condition of the reaction like temperature, pressure, catalyst etc. is written above or below the arrow in the chemical equation.
(a) If the reactant or product is present as a solution of water, it is represented as:
(i) (s)
(ii) (l)
(iii) (aq)
(iv) ↓
Ans.
So, the correct a nswer is (iii) (aq)
(b) The correct way to represent the evolution of gas, is to use which of the following symbol:
(i) ↓
(ii) →
(iii) ↑
(iv) (g)
Ans.
So, the correct a nswer is (iii) ↑
(c) Complete the missing variable given as X and Y in the following reaction:
2Na (s) + 2H 2 O (l) → 2NaOH (X) + H 2 (Y)
(i) (aq) and (g)
(ii) (s) and (g)
(iii) (g) and (l)
(iv) (g) and (aq)
Ans. Here,
- Since Na is reacting with water , the NaOH produced will be in aqueous medium , hence ( aq) symbol will be used.
- H 2 is a gas which is evolved during the reaction, so we use the symbol (g) for it.
So, the correct answer is (i) (aq) and (g)
(d) Which of the following reactions is balanced?
(i) NaCl + 2H 2 O → 2NaOH + 2Cl 2 + H 2
(ii) 2NaCl + H 2 O → 2NaOH + 2Cl 2 + H 2
(iii) 2NaCl + 2H 2 O → 2NaOH + Cl 2 + H 2
(iv) 2NaCl + 2H 2 O → NaOH + Cl 2 + H 2
Ans.
Explanation:
A balanced chemical equation is one in which the number of atoms of both reactants and products are equal.
In reaction I:
|
Na |
H |
O |
Cl |
|
|
Reactant |
1 |
4 |
2 |
1 |
|
Product |
2 |
4 |
2 |
4 |
Since the number of Na and Cl atoms in reactant and product is not equal, it is not a balanced equation.
In reaction II:
|
Na |
H |
O |
Cl |
|
|
Reactant |
2 |
2 |
1 |
2 |
|
Product |
2 |
4 |
2 |
4 |
Since the number of H, O and Cl atoms in reactant and product is not equal. It is not a balanced equation.
In reaction III:
|
Na |
H |
O |
Cl |
|
|
Reactant |
2 |
4 |
2 |
2 |
|
Product |
2 |
4 |
2 |
2 |
Since the number of all atoms in reactants and products is equal, it is a balanced equation.
In Reaction IV:
|
Na |
H |
O |
Cl |
|
|
Reactant |
2 |
4 |
2 |
2 |
|
Product |
1 |
3 |
1 |
2 |
Since the number of Na, H, and O atoms is not equal in reactant and product, it is not a balanced equation.
So, the correct
answer is (iii) 2NaCl + 2H
2
O → 2NaOH + Cl
2
+ H
2
(e) Which of the following reactions is correct?
(i) Mg (aq) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2 ↑
(ii) Mg (s) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2 ↑
(iii) Mg (s) + H 2 SO 4 (l) → MgSO 4 (l) + H 2 (g)
(iv) Mg (s) + H 2 SO 4 (l) → MgSO 4 (s) + H 2
Ans. (ii) Mg (s) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2 ↑
Explanation:
A balanced chemical equation is one in which the number of atoms of both reactants and products are equal.
In reaction I:
|
Mg |
H |
O |
S |
|
|
Reactant |
1 |
2 |
2 |
1 |
|
Product |
1 |
2 |
4 |
In reaction II:
|
Mg |
H |
O |
S |
|
|
Reactant |
1 |
2 |
4 |
1 |
|
Product |
1 |
2 |
4 |
1 |
Since the number of all atoms in reactants and products is equal, it is a
balanced
equation.
In reaction III:
|
Mg |
H |
O |
S |
|
|
Reactant |
||||
|
Product |
In Reaction IV:
|
Mg |
H |
O |
S |
|
|
Reactant |
||||
|
Product |
