Science (English Medium) Class 12 - CBSE Question Bank Solutions

Assertion: Order of the reaction can be zero or fractional.

Reason: We cannot determine order from balanced chemical equation.

Assertion: Order and molecularity are same.

Reason: Order is determined experimentally and molecularity is the sum of the stoichiometric coefficient of rate determining elementary step.

Assertion: The enthalpy of reaction remains constant in the presence of a catalyst.

Reason: A catalyst participating in the reaction, forms different activated complex and lowers down the activation energy but the difference in energy of reactant and product remains the same.

Assertion: Rate constants determined from Arrhenius equation are fairly accurate for simple as well as complex molecules.

Reason: Reactant molecules undergo chemical change irrespective of their orientation during collision.

Why does the white precipitate of silver halide become coloured in the presence of dye eosin.

When copper ore is mixed with silica, in a reverberatory furnace copper matte is produced. The copper matte contains ______.

Which of the following options are correct?

(i) Cast iron is obtained by remelting pig iron with scrap iron and coke using hot air blast.

(ii) In extraction of silver, silver is extracted as cationic complex.

(iii) Nickel is purified by zone refining.

(iv) Zr and Ti are purified by van Arkel method.

In the extraction of aluminium by Hall-Heroult process, purified \[\ce{Al2O3}\] is mixed with \[\ce{CaF2}\] to:

(i) lower the melting point of \[\ce{Al2O3}\].

(ii) increase the conductivity of molten mixture.

(iii) reduce \[\ce{Al^{3+}}\] into \[\ce{Al(s)}\].

(iv) acts as catalyst.

Which of the following reactions occur during calcination?

(i) \[\ce{CaCo3 -> CaO + CO2}\]

(ii) \[\ce{2FeS2 + 11/2 O2 -> Fe2O3 + 4SO2}\] 

(iii) \[\ce{Al2O3. {x}H2O -> Al2O3 + {x}H2O}\]

(iv)  \[\ce{ZnS + 3/2 O2 -> ZnO + SO2}\]

The main reactions occurring in blast furnace during extraction of iron from haematite are:

(i) \[\ce{Fe2O3 + 3CO -> 2Fe + 3CO2}\]

(ii) \[\ce{FeO + SiO2 -> FeSiO3}\] 

(iii) \[\ce{Fe2O3 + 3C -> 2Fe + 3CO}\]

(iv) \[\ce{CaO + SiO2 -> CaSiO3}\]

Although carbon and hydrogen are better reducing agents but they are not used to reduce metallic oxides at high temperatures. Why?

Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.

Which of the following statements is wrong?

The oxidation state of central atom in the anion of compound \[\ce{NaH2PO2}\] will be ______.

If chlorine gas is passed through hot NaOH solution, two changes are observed in the oxidation number of chlorine during the reaction. These are :

(i) 0 to +5

(ii) 0 to +3

(iii) 0 to –1

(iv) 0 to +1

Which of the following options are not in accordance with the property mentioned against them?

Which of the following statements are correct for \[\ce{SO2}\] gas?

(i) It acts as bleaching agent in moist conditions.

(ii) It’s molecule has linear geometry.

(iii) It’s dilute solution is used as disinfectant.

(iv) It can be prepared by the reaction of dilute \[\ce{H2SO4}\] with metal sulphide.

Which of the following orders are correct as per the properties mentioned against each?

Match the species given in Column I with the shape given in Column II and mark the correct option.

Match the items of Columns I and II and mark the correct option.