12th Chemistry - Book Back Answers - Unit 9 Electro Chemistry - English Medium Guides

  

 

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Tamil Nadu Board 12th Standard Chemistry - Unit 9: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Unit 9 from the Tamil Nadu State Board 12th Standard Chemistry textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.

    We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.

    By going through this material, you’ll gain a strong understanding of Unit 9 along with the corresponding book back questions and answers (PDF format).

Question Types Covered:

• 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following 
• 2 Mark Questions: Answer briefly 
• 3, 4, and 5 Mark Questions: Answer in detail

All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.

All the best, Class 12 students! Prepare well and aim for top scores. Thank you!

I. Multiple Choice Questions

1. The number of electrons that have a total charge of 9650 coulombs is

a) 6.22 ×10²³

b) 6.022 ×10²⁴

c) 6.022 ×10²²

c) 6.022 ×10⁻³⁴

Answer Key:

c) 6.022 ×10²²

 

2. Consider the following half cell reactions:

Mn²⁺ + 2e⁻ $\mathbf{\to }$ Mn E° = -1.18V

Mn²⁺ $\mathbf{\to }$Mn³⁺ + e⁻ E° = -1.51V

The E° for the reaction 3Mn²⁺ $\mathbf{\to }$Mn+2Mn³⁺, and the possibility of the forward reaction are respectively.

a) 2.69V and spontaneous

b) -2.69 and non spontaneous

c) 0.33V and Spontaneous

d) 4.18V and non spontaneous

Answer Key:

b) -2.69 and non spontaneous

  

3. The button cell used in watches function as follows

Zn (s) + Ag₂O (s) + H₂O (l) $$\begin{gathered} \text{ \\ ⇌} \end{gathered}$$ 2 Ag (s) + Zn²⁺(aq) + 2OH^-(aq) the half cell

potentials are Ag₂O (s) + H₂O (l) + 2e⁻  $\mathbf{\to }$ 2Ag (s) + 2OH^- (aq) E° = 0.34V

and Zn (s) $\mathbf{\to }$Zn²⁺ (aq) + 2e⁻ E° = 0.76V . The cell potential will be

a) 0.84V

b) 1.34V

c) 1.10V

d) 0.42V

Answer Key:

c) 1.10V 

  

4. The molar conductivity of a 0.5 mol dm^-3 solution of AgNO₃ with electrolytic conductivity of 5.76 ×10⁻³ S cm⁻¹at 298 K is

a) 2.88 S cm²mol^-1

b) 11.52 S cm²mol^-1

c) 0.086 S cm²mol^-1

d) 28.8 S cm²mol^-1

Answer Key:

b) 11.52 S cm²mol^-1

  

5.

Electrolyte	KCl	KNO3	HCl	NaOAC	NaCl
${\mathrm{\Lambda }}_{-}$ (S cm2mol-1)	149.9	145.0	426.2	91.0	126.5

Calculate ${\mathbf{\Lambda }}_{\mathbf{°}}^{\mathbf{H}\mathbf{O}\mathbf{A}\mathbf{C}}$ using appropriate molar conductances of the electrolytes listed above at infinite dilution in water at 25°C .

a) 517.2

b) 552.7

c) 390.7

d) 217.5

Answer Key:

c) 390.7 

  

6. Faraday constant is defined as

a) charge carried by 1 electron

b) charge carried by one mole of electrons

c) charge required to deposit one mole of substance

d) charge carried by 6.22 ×10¹⁰ electrons.

Answer Key:

b) charge carried by one mole of electrons

  

7. How many faradays of electricity are required for the following reaction to occur  

MnO₄^- $\mathbf{\to }$Mn²⁺

a) 5F

b) 3F

c) 1F

d) 7F

Answer Key:

a) 5F 

  

8. A current strength of 3.86 A was passed through molten Calcium oxide for 41minutes and 40 seconds. The mass of Calcium in grams deposited at the cathode is (atomic mass of Ca is 40g / mol and 1F = 96500C).

a) 4

b) 2

c) 8

d) 6

Answer Key:

b) 2 

  

9. During electrolysis of molten sodium chloride, the time required to produce 0.1mole of chlorine gas using a current of 3A is

a) 55 minutes

b) 107.2 minutes

c) 220 minutes

d) 330 minutes

Answer Key:

b) 107.2 minutes 

  

10. The number of electrons delivered at the cathode during electrolysis by a current of 1A in 60 seconds is (charge of electron = 1.6 ×10⁻¹⁹C)

a) 6.22 ×10²³

b) 6.022 ×10²⁰

c) 3.75 ×10²⁰

d) 7.48 ×10²³

Answer Key:

c) 3.75 ×10²⁰

  

11. Which of the following electrolytic solution has the least specific conductance

a) 2N

b) 0.002N

c) 0.02N

d) 0.2N

Answer Key:

b) 0.002N 

  

12. While charging lead storage battery

a) PbSO₄ on cathode is reduced to Pb

b) PbSO₄ on anode is oxidised to PbO₂

c) PbSO₄ on anode is reduced to Pb

d) PbSO₄ on cathode is oxidised to Pb

Answer Key:

c) PbSO₄ on anode is reduced to Pb 

  

13. Among the following cells

I) Leclanche cell

II) Nickel – Cadmium cell

III) Lead storage battery

IV) Mercury cell

Primary cells are

a) I and IV

b) I and III

c) III and IV

d) II and III

Answer Key:

a) I and IV 

  

14. Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because

a) Zinc is lighter than iron

b) Zinc has lower melting point than iron

c) Zinc has lower negative electrode potential than iron

d) Zinc has higher negative electrode potential than iron

Answer Key:

d) Zinc has higher negative electrode potential than iron

  

15. Assertion : pure iron when heated in dry air is converted with a layer of rust.

Reason : Rust has the compositionFe₃O₄

a) if both assertion and reason are true and reason is the correct explanation of assertion.

b) if both assertion and reason are true but reason is not the correct explanation of

assertion.

c) assertion is true but reason is false

d) both assertion and reason are false.

Answer Key:

d) both assertion and reason are false.

  

16. In H₂-O₂ fuel cell the reaction occurs at cathode is

a) O₂(g) + 2H₂O (l) + 4e⁻ $\mathbf{\to }$ 4OH⁻ (aq)

b) H+(aq) + OH‑ (aq) $\mathbf{\to }$ H₂O (2l)

c) 2H₂(g) + O₂(g) $\mathbf{\to }$2H₂O (g)

d) H⁺ e^-  $\mathbf{\to }$ $\raisebox{1ex}{$\mathbf{1}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{2}$}\right.$H₂

Answer Key:

a) O₂(g) + 2H₂O (l) + 4e⁻ $\mathbf{\to }$ 4OH⁻ (aq)

 

17. The equivalent conductance of $\raisebox{1ex}{$\mathbf{M}$}\!\left/ \!\raisebox{-1ex}{$\mathbf{36}$}\right.$ solution of a weak monobasic acid is 6 mho cm₂ equivalent –1 and at infinite dilution is 400 mho cm² equivalent ^–1. The dissociation constant of this acid is

a) 1.25 ×10⁻⁶

b) 6.25 ×10⁻⁶

c) 1.25 ×10⁻⁴

d) 6.25 ×10⁻⁵

Answer Key:

b) 6.25 ×10⁻⁶

  

18. A conductivity cell has been calibrated with a 0.01M, 1:1 electrolytic solution (specific conductance ( 𝛋 =1.25 x 10^-3 S cm^-1) in the cell and the measured resistance was 800 Ω at 25°C . The cell constant is,

a) 10⁻¹ c m⁻¹

b) 10¹ c m⁻¹

c) 1 c m⁻¹

d) 5.7 ×10⁻¹²

Answer Key:

c) 1 c m⁻¹

  

19. Conductivity of a saturated solution of a sparingly soluble salt AB (1:1 electrolyte) at 298K is 1.85 ×10⁻⁵ S m⁻¹. Solubility product of the salt AB at 298K $\mathbf{(}{\mathbf{\Lambda }}_{\mathbf{M} }^{\mathbf{°}}{\mathbf{)}}_{\mathbf{A}\mathbf{B}}$= 14 ×10⁻³ S m² mol⁻¹ .

a) 5.7 ×10⁻¹²

b) 1.32 ×10⁻¹²

c) 7.5 ×10⁻¹²

d) 1.74 ×10⁻¹²

Answer Key:

d) 1.74 ×10⁻¹²

 

20. In the electrochemical cell: Zn|ZnSO₄ (0.01M)|| CuSO₄ (1.0M) Cu, the emf of this Daniel cell is E₁. When the concentration of is changed to 1.0M and that CuSO₄ changed to 0.01M, the emf changes to E₂. From the above, which one is the relationship between E₁ and E₂?

a) E₁ < E₂

b) E₁ > E₂

c) E_{1 ≥}  E₂

d) E₁ = E₂

Answer Key:

b) E₁ > E₂

  

21. Consider the change in oxidation state of Bromine corresponding to different emf values as shown in the diagram below:

$\mathbf{B}\mathbf{r}{\mathbf{O}}_{\mathbf{4}}^{\mathbf{-}}\stackrel{\mathbf{1.82}\mathbf{V}}{\mathbf{\to }}\mathbf{B}\mathbf{r}{\mathbf{O}}_{\mathbf{3}}^{\mathbf{-}}\stackrel{\mathbf{1.5}\mathbf{V}}{\mathbf{\to }}\mathbf{H}\mathbf{B}\mathbf{r}\mathbf{O}\stackrel{\mathbf{1.595}\mathbf{V}}{\mathbf{\to }}\mathbf{B}{\mathbf{r}}_{\mathbf{2}}\stackrel{\mathbf{1.0652}\mathbf{V}}{\mathbf{\to }}\mathbf{B}{\mathbf{r}}^{\mathbf{-}}$ 

Then the species undergoing disproportionation is

a) Br₂

b) $\mathbf{B}\mathbf{r}{\mathbf{O}}_{\mathbf{4}}^{\mathbf{-}}$

c) $\stackrel{}{\mathbf{}}$$\mathbf{B}\mathbf{r}{\mathbf{O}}_{\mathbf{3}}^{\mathbf{-}}$

d) HBrO 

Answer Key:

d) HBrO 

  

22. For the cell reaction

2Fe³⁺(aq) + 2l⁻(aq) $\mathbf{\to }$2Fe²⁺ (aq) + l₂(aq)

E°.24V cell o = at 298K. The standard Gibbs energy (Δ, G°) of the cell reactions is:

a) -46.32 KJ mol⁻¹

b) -23.16 KJ mol⁻¹

c) 46.32 KJ mol⁻¹

d) 23.16 KJ mol⁻¹

Answer Key:

a) -46.32 KJ mol⁻¹

  

23. A certain current liberated 0.504gm of hydrogen in 2 hours. How many grams of copper can be liberated by the same current flowing for the same time through copper sulphate solution

a) 31.75

b) 15.8

c) 7.5

d) 63.5

Answer Key:

b) 15.8 

  

24. A gas X at 1 atm is bubbled through a solution containing a mixture of 1MY^- and 1MZ^- at 25^oC. If the reduction potential of Z>Y>X, then

a) Y will oxidize X and not Z

b) Y will oxidize Z and not X

d) Y will oxidize both X and Z

d) Y will reduce both X and Z

Answer Key:

a) Y will oxidize X and not Z 

  

25. Cell equation : A²⁺+ 2B^- $\mathbf{\to }$A+2B

A^{2 +} + 2e^- $\mathbf{\to }$A E^o = +0.34V and log₁₀K = 15.6 at 300K for cell reactions find E^o for

B⁺ + e⁻ $\mathbf{\to }$B

a) 0.80

b) 1.26

c) -0.54

d) -10.94

Answer Key:

a) 0.80  

 

II. Short Answer Questions.

12th Chemistry

III. Long Answer Questions. 

12th Chemistry

IV. Exercise.   

12th Chemistry