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Electrochemistry — Chemistry STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceChemistryElectrochemistry4 Marks
Question
The potential of each electrode is known as electrode potential. Standard electrode potential is the potential when concentration of each species taking part in electrode reaction is unity and the reaction is taking place at 298K. By convention, the standard electrode potential of hydrogen (SHE) is 0.0V. The electrode potential value for each electrode process is a measure of relative tendency of the active species in the process to remain in the oxidised/ reduced form. The negative electrode potential means that the redox couple is stronger reducing agent than $\frac{\text{H}^+}{\text{H}_2}$ couple. A positive electrode potential means that the redox couple is a weaker reducing agent than the $\frac{\text{H}^+}{\text{H}_2}$ couple. Metals which have higher positive value of standard reduction potential form the oxides of greater thermal stability.

In these questions (Q. No. i-iv), a statement of assertion followed by a statement ofreason is given. Choose the correct answer out of the following choices.

  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
  1. Assertion: An electrochemical cell can be set-up only if the redox reaction is spontaneous.

Reason: A reaction is spontaneous if the free energy change is negative.

  1. Assertion: The standard electrode potential of hydrogen is 0.0V.

Reason: It is by convention.

  1. Assertion: The more negative is the standard reduction potential, greater is its ability to displace H2 from acid.

Reason: Strength of reducing agent increases with the increase in negative value of the standard reduction potential.

  1. Assertion: The negative value of standard reduction potential means that reduction takes place on this electrode with reference to hydrogen electrode.

Reason: The standard electrode potential of a half cell has a fixed value.

  1. Assertion: The absolute value of electrode potential cannot be determined experimentally.

Reason: The electrode potential values are generally determined with respect to SHE.

✓

Answer

  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

Explanation:

More negative is the standard reduction potential, greater is its ability to displace hydrogen from acid.

  1. (d) Assertion is wrong statement but reason is correct statement.

Explanation:

A negative value of standard reduction potential means that oxidation takes place on the electrode with reference to SHE.

  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

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  2. $\approx100%$

  3. 36%
  4. 64%
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Read the passage given below and answer the following questions:

In haloalkanes, when a nucleophile stronger than the halide ion approaches the positively charged carbon atom of an alkyl halide, the halogen atom along with its bonding electron pair gets displaced and a new bond with the carbon and the nucleophile is formed. These reactions are called nucleophilic substitution reactions.

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Reagent
Nucleophile (Nu-)
Substitution product R-Nu
Class of main product
1.
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-OH
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2.
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I-
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$\text{R'}\ddot{\text{N}}\text{H}_2$
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Sec. amine
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6.
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In these questions (Q. No. i-iv), a statement of assertion followed by a statement ofreason is given. Choose the correct answer out of the following choices.

  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
  1. Assertion: Alkyl halides are hydrolysed to alcohols by moist silver oxide.

Reason: RCI is hydrolysed to ROH easily but reactions slow down on addition of KI.

  1. Assertion: Alkyl halides fonn alkenes when heated above 300ºC.

Reason: CH3CH21 reacts slowly with strong base as compared to CD3CH2I.

  1. Assertion: RBr reacts with AgNO2 to give nitroalkane.

Reason: Silver nitrite (AgNO2) is an ionic compound, therefore the negative charge on nitrogen is the attacking site.

  1. Assertion: The nucleophilic substitution of vinyl chloride is difficult than ethyl chloride.

Reason: Vinyl group is electron donating group.

  1. Assertion: 2-Bromobutane on reaction with sodium ethoxide in ethanol gives 1-butene as the major product.

Reason: 1-Butene is less stable than 2-butene.

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Read the passage given below and answer the following questions:

The addition reaction of enol or enolate to the carbonyl functional group of aldehyde or ketone is known as aldol addition. The $\beta-$ hydroxyaldehyde or $\beta-$hydroxyketone so obtained undergo dehydration in second step to produce a conjugated enone. The first part of reaction is an addition reaction and the second part is an elimination reaction. Carbonyl compound having $\propto-$hydrogen undergoes aldol condensation reaction.

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  1. Condensation reaction is the reverse of which of the following reaction?
  1. Lock and key hypothesis.
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  1. Which of the following compounds would be the main product of an aldol condensation of acetaldehyde and acetone?
  1. CH3CH = CHCHO
  2. CH3CH = CHCOCH3
  3. (CH3)2C = CHCHO
  4. (CH3)2C = CHCOCH3
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  1. HCHO
  2. CH3CH2OH
  3. C6H5CHO
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  1. Which of the following does not undergo aldol condensation?
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  3. CH3COCH3
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What change in the concentration of H₂ will triple the rate of reaction?
(c). Suppose a reaction between A and B, was experimentally found to be first order with respect to both A and B. So the rate equation is:
Rate = k[A][B]
Which of these two mechanisms is consistent with this experimental finding? Why?
Mechanism 1
A → C + D (slow)
B+C → E (fast)
Mechanism 2
A+B →C + D (slow)
C → E (fast)
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Read the passage given below and answer the following questions:

RCONH2 is converted into RNH2 by means of Hoffmann bromamide degradation. During the reaction amide is treated with Br2 and alkali to get amine. This reaction is used to descend the series in which carbon atom is removed as carbonate ion $(\text{CO}^{2-}_3)$ Hoffmann bromide degradation reaction can be written as:

The following questions are multiple choice questions. Choose the most appropriate answer:

  1. Hoffmann bromamide degradation is used for the preparation of
  1. Primary amines.
  2. Secondary amines.
  3. Tertiary amines.
  4. Secondary aromatic amines.
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  1. Formation of (i)
  2. Formation of (ii)
  3. Formation of (iii)
  4. Formation of (iv).
  1. Which of the following are used for the conversion of (i) to (ii)?
  1. KBr
  2. KBr + CH3ONa
  3. KBr + KOH
  4. Br2 + KOH
  1. Identify Bin the following reaction.

$\text{R}-\text{C}\equiv\text{N}\xrightarrow[\text{(Partially hydrolysis) }]{\text{Cone. HCI}}\text{A}\xrightarrow{\frac{\text{Br}_2}{\text{KOH}}}\text{B}$

  1. RCONH2
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  3. RNHBr
  4. R = N = C = O
  1. What are the constituent amines formed when the mixture of (i) and (ii) undergoes Hoffmann bromamide degradation?

 

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Read the passage given below and answer the following questions:

Transition metal oxides are compounds fanned by the reaction of metals with oxygen at high temperature. The highest oxidation number in the oxides coincides with the group number. In vanadium, there is a gradual change from the basic V2O3 to less basic V2O4 and to amphoteric V2O5· V2O4 dissolves in acids to give VO2+ salts. Transition metal oxides are commonly utilized for their catalytic activity and semi conductive properties. Transition metal oxides are also frequently used as pigments in paints and plastic. Most notably titatnium dioxide. One of the earliest application of transition metal oxides to chemical industry involved the use of vanadium oxide for catalytic oxidation of sulfur dioxide to sulphuric acid. Since then, many other applications have emerged, which include benzene oxidation to maleic anhydride on vandium oxides; cyclohexane oxidation to adipic acid on cobalt oxides. An important property of the catalyst material used in these processes is the ability of transition metals to change their oxidation state under a given chemical potential of reductants and oxidants.

The following questions are multiple choice questions. Choose the most appropriate answer:

  1. Which oxide of vanadium is most likely to be basic and ionic?
  1. VO
  2. V2O3
  3. VO2
  4. V2O5
  1. Vanadyl ion is:
  1. $\text{VO}^{2+}$
  2. $\text{VO}^{+}_2$
  3. $\text{V}_{2}\text{O}^+$
  4. $\text{VO}^{3-}_4$
  1. Which of the following statements is false?
  1. With fluorine vanadium can form VF5.
  2. With chlorine vanadium can form VCl5.
  3. Vanadium exhibits highest oxidation state in oxohalides VOCl3, VOBr3 and fluoride VF5.
  4. With iodine vanadium cannot form Vl5 due to oxidising power of V5+ and reducing nature of I-.
  1. The oxidation state of vanadium in V2O5 is:
  1. $\frac{+5}{2}$

  2. +7
  3. +5
  4. +6
  1. Identify the oxidising agent in the following reaction.

V2O5 + 5Ca → 2V + 5CaO

  1. V2O5
  2. Ca
  3. V
  4. None of these.
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