Redox Reactions

The heat of combustion of carbon to CO₂ is -393.5 kJ/ mol. The heat released upon formation of 35.2 gm of CO₂ from carbon and oxygen gas is:

• +315 kJ

• -31.5 kJ

• -315 kJ

• +31.5 kJ

Which of the following substances acts as an oxidising as well as a reducing agent ?

• Na₂O

• SnCl₂

• Na₂O₂

• NaNO₂

The compound having the lowest oxidation state of iron is :

• K₄Fe(CN)₆

• K₂FeO₄

• Fe₂O₃

• Fe(CO)₅

3ClO^-(aq) → ClO^- + 2Cl is an example of

• Oxidation reaction

• reduction reaction

• disproportionation reaction

• decomposition reaction

When K₂Cr₂O₇ is converted into K₂CrO₄, the change in oxidation number of chromium is :

• 0

• 5

• 7

• 9

In the equation

CrO${}_4^{2-}$ + SO${}_3^{2-} \to \mathrm{Cr}(\mathrm{OH}{)}_4^{-} + {\mathrm{SO}}_4^{2-}$

the oxidation number of Cr changes from

• +6 to +4

• +6 to +3

• +8 to +4

• +4 to +3

Which quantities are conserved in all oxidation- reduction reactions?

• Charge only

• Mass only

• Both charge and mass

• Neither charge nor mass

The oxidation number of chromium in CrO₅ is

• +6

• +5

• +10

• 0

Silver metal is recovered industrially by using the chemistry shown below. Which of the following statements is/are not true?

2K[Ag(CN)₂] +Zn→ K₂[Zn(CN)₄] + 2Ag

• only Ag has been oxidised and Zn reduced

• (a), (c), (d)

• Both Ag and Zn have been oxidised

• Both Ag and Zn have been reduced

Which of the following does not/do not represent the correct equivalent mass of Cr₂O${}_7^{2-}$ in the reaction Cr₂O${}_7^{2-}$+ 14 H⁺ + 6e^- → 2Cr³⁺ + 7H₂O.

• The molar mass of dichromate

• One third of the molar mass of dichromate

• One half of the molar mass of dichromate

• all of the above