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Class 12th Chemistry Solutions

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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Vishal Baghel

Contributor-Level 10

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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Class 12th Chemistry

Lyophilic sols are more stable than lyophobic sols because:

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alok kumar singh

Contributor-Level 10

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

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Class 12th Chemistry

In stratosphere most of the ozone formation is assisted by:

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alok kumar singh

Contributor-Level 10

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

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

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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Vishal Baghel

Contributor-Level 10

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

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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Class 12th Chemistry

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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Vishal Baghel

Contributor-Level 10

Mass of organic compound = 0.2 gram

$n_{A g B r} = \frac{0.188}{188} m o l$

= 0.001 mol

$n_{B r} = n_{A g B r} = 0.001 m o l e$

Mass of Br = 0.001 * 80g

= 0.08 g

Mass & of Br = $\frac{0.08}{0.2} * 100 %$

= 40 %

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Class 12th Chemistry

Potassium permanganate on heating at 518K gives a product which is:

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alok kumar singh

Contributor-Level 10

$2 K M n O_{4} \overset{Δ}{\to} {K_{2} M n O_{4}}_{(g r e e n)}^{+ 6} + \underset{(b l a c k)}{M n O_{2}} + O_{2}$

Mn⁶⁺ has one unpaired electron so paramagnetic and has green colour.

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Class 12th Coordination Compounds

1 mol of an octahedral metal complex with formula MCl₃ $\cdot$ 2L on reaction with excess of AgNO₃ gives 1 mol of AgCl. The denticity of Ligand L is________(integer answer)

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