1.Which of the following is not a physical change?
(a) Boiling of water to give water vapour. (b) Melting of ice to give water. (c) Dissolution of salt in water. (d) Combustion of Liquefied Petroleum Gas (LPG). |
Answer
Answer: (d) Combustion of Liquefied Petroleum Gas (LPG).
Explanation: Since the combustion of Liquefied Petroleum Gas (LPG) produces new substances, a lot of heat is produced along with carbon dioxide and water vapour. It is also irreversible in nature. So it is a chemical change.
However, boiling of water to give water vapour, melting of ice to give water and dissolution of salt in water are physical changes, as here no new substance is formed, only the physical state of the substance changes.
A physical change does not produce a new substance although the initial and final substances appear different and it is reversible.
During a chemical change, the chemical composition of the substance changes and new substances with new properties are formed. Energy is either released or absorbed during a chemical change and it is irreversible.
During a chemical change, the chemical composition of the substance changes and new substances with new properties are formed. Energy is either released or absorbed during a chemical change and it is irreversible.
2.Which among the following is (are) double displacement reaction(s)?
(a) (I) and (IV) (b) Only (II) (c) (I) and (II) (d) (III) and (IV) |
Answer
Answer: (b) only (II)
Explanation: A double displacement reaction involves the displacement of two ions of two different compounds that results in the formation of new compounds. Here, only in reaction (II), ions of both reactants are exchanged and two entirely different compounds are formed. For example.
Na2SO4 + BaCl2 → BaSO4(s) (White ppt) + 2NaCl(aq)
In a double displacement reaction, exchange of ions takes place i.e., SO42- exchange place with Cl– ion. It is also called a precipitation reaction as BaSO4 is precipitated as insoluble salt in the solution.
3.When copper turnings are added to silver nitrate solution, a blue coloured solution is formed after some time. It is because copper:
(a) (I) and (II) (b) (II) and (III) (c) (I) and (III) (d) (II) and (IV) |
Answer
Answer: (c) (I) and (III)
Explanation: Copper is placed above silver in electrochemical series and thus reaction occurs
Cu + 2Ag+ → Cu2+ + 2Ag
4.Balance the following chemical equations :
Answer:Answer: (a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O (b) 2NaOH + H2SO4 → Na2SO4 + 2H2O (c) NaCl + AgNO3 → AgCl + NaNO3 (d) BaCl2 + H2SO4 → BaSO4 + 2HCl
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