Class 12th

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(a) $C a l a m i n e : Z n C O_{3}$

(b) Malachite : $C u C O_{3} . C u {(O H)}_{2}$

(c) Siderite : FeCO₃

(d) Sphalerite : ZnS

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Class 12th Redox Reactions

When 10 mL of an aqueous solution of KMnO₄ was titrated in acidic medium, equal volume of 0.1 M of an aqueous solution of ferrous sulphate was required for complete discharge of colour. The strength of KMnO₄ is grams per litre is________* 10^-2. (Nearest integer)

[Atomic mass of K = 39, Mn = 55, O = 16]

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Let molarity of KMnO₄ = x

$K M n O_{4} + F e S O_{4} \to F e_{2} {(S O_{4})}_{3} + M n^{2 +}$

n = 5 n = 1 Ferric sulphate

equivalent of KMnO₄ = equivalent of FeSO₄

5 * x * 10 = 1 * 0.1 * 10

x = 0.02 M

Strength = (0.02 * 158) = 3.16g/L

= 316 * 10^-2 g/L

Ans. = 316

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The number of f electrons in the ground state electronic configuration Np (Z = 93) is_________.

(Nearest integer)

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$\underset{(z = 93)}{N p} \Rightarrow 1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{2} 3 d^{10} 4 p^{6} 5 s^{2}$

$4 d^{10} 5 p^{6} 6 s^{2} 4 f^{14} 5 d^{10} 6 p^{6} 7 s^{2} 5 f^{4} 6 d^{1}$

Total number of f-electrons = 14 + 4 = 18 electrons

Ans. = 18

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The number of moles of CuO, that will be utilized in Dumas method for estimating nitrogen in a sample of 57.5g of N, N-dimethylaminopentane is________ * 10^-2. (Nearest integer).

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Dumas method,

Moles of N in N, N-dimethylaminopentane (C₇H₁₇N)

$= \frac{57.5}{115} = 0.5 m o l e$

$C_{7} H_{17} N + \frac{45}{2} C u O \to 7 C O_{2} + \frac{17}{2} H_{2} O + \frac{1}{2} N_{2} + \frac{45}{2} C u$

$\frac{n_{C u O}}{(\frac{45}{2})} = \frac{n_{c_{7} H_{17} N}}{1}$

$n_{C u O} = (\frac{45}{2}) * 0.5 m o l$

= 11.25 mol

= 1125 * 10^-2 mol

Ans. = 1125

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The compound/s which will show significant intermolecular H-bonding is/are:

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Class 12th Chemistry Solutions

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(a) Shows intra molecular H-bonding.

(b) Shows inter molecular H-bonding.

(c) It does not shows intermolecular H-bonding due to high steric hindrance at o-position of benzene ring.

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1 kg on 0.75 molal aqueous solution of sucrose can be cooled up to -4°C before freezing. The amount of ice (in g) that will be separated out is__________. (Nearest integer)

[Given : K_f(H₂O) = 1.86K kg mol^-1]

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Let mass of water initially = x gram

Mass of sucrose = (1000 – x) gram

Mole of sucrose = $\frac{1000 - x}{342} m o l$

$?$ 0.75 molal Þ 0.75 mole solute in 1 kg of solvent

$0.75 = \frac{(1000 - x) / 342}{x / 1000} [m o l a l i t y = \frac{n_{s o l u t e}}{M_{s o l v e n t} (k g)}]$

$4 = \frac{\frac{(1000 - 795.86) * 1.86}{342}}{a}$

a = 0.2775kg or 277.5 gram

Ice separated = (795.86 – 277.5) gram

= 518.3 gram

Ans. = 518 (the nearest integer)

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Lyophilic sols are more stable than lyophobic sols because:

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In the lyophilic colloids, the colloidal particles are extremely solvated.

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In stratosphere most of the ozone formation is assisted by:

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$O_{2} (g) \to_{}^{U V} O (g) + O (g)$

$O (g) + O_{2} (g) \overset{U V}{\to} O_{3} (g)$

Ozone in the stratosphere is a product of UV radiations acting on O₂ molecule.

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Class 12th Redox Reactions

The reaction that occurs in a breath analyser, a device used to determine the alcohol level in a person's blood stream is

$2 K_{2} C r_{2} O_{7} + 8 H_{2} S O_{4} + 3 C_{2} H_{6} O \overset{}{\to} 2 C r_{2} {(S O_{4})}_{3} + 3 C_{2} H_{4} O_{2} + 2 K_{2} S O_{4} + 11 H_{2} O$

If the rate of appearance of Cr₂(SO₄)₃ is 2.67 mol min^-1 at a particular time, the rate of disappearance of C₂H₆O at the same time is________mol min^-1. (Nearest integer)

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$2 K_{2} C r_{2} O_{7} + 8 H_{2} S O_{4} + 3 C_{2} H_{6} O \to 2 C r_{2} {(S O_{4})}_{3} + 3 C_{2} H_{4} O_{2} + 2 K_{2} S O_{4} + 11 H_{2} O$

Given that, rate of appearance of Cr₂(SO₄)₃ = $+ \frac{d [C r_{2} {(S O_{4})}_{3}]}{d t} = 2.67 m o l e / m i n$

LHS RHS

$(\frac{R a t e o f d i s a p p e a r a n c e o f C_{2} H_{6} O}{3}) = (\frac{R a t e o f a p p e a r a n c e o f C r_{2} {(S O_{4})}_{3}}{2})$

Rate of disappearance of C₂H₆O = $\frac{2.67 * 3}{2} m o l / m i n$

Rate of disappearance of C₂H₆O = 4.005 mol /min

Ans. = 4 (nearest integer)

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In Carius method for estimation of halogens, 0.2g of an organic compound gave 0.188g of AgBr. The percentage of bromine in the compound is_________. (Nearest integer)

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