Chemistry Test

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Chemistry Test - 33

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Weekly Quiz Competition

Question 1
1 / -0

For the indicator HIn the ratio $\frac{[\mathrm{In}]}{[\mathrm{HIn}]}$is 7.0 at pH of 4.3. K_eq for the indicator is :

[Given log 7 = 0.845 and Antilogo(0.545)=3.5

A

B

C

D

Solution

For weak organic acid indicators

pH = pK_a+ log In - HIn

4.3 = pK_a+ log 7

pK_a= 4.3 - 0.845 = 3.455

pK_a= -log₁₀K_a

K_a= Antilog (-pK_a)

K_a= Antilog (-3.455)

= 3.5 x 10^-4
Hence, the correct option is (A)
Question 2
1 / -0

A
o-bromotoluene

B
m-bromotoluene

C
p-bromotoluene

D
3-bromo-2, 2, 6-trichlorotoluene

Solution

Hence, the correct option is (B)
Question 3
1 / -0

Glyptal is classified as a :

A
Polyolefin

B
Polyester

C
Polyamide

D
Polyether

Solution

Glyptal is a polymer of ethylene glycol and phthalic acid.

The continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene, whose repeating unit is based on ethylene monomer. However, other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant.

Oxygen is also commonly present in polymer backbones, such as those of polyethylene glycol, polysaccharides (in glycosidic bonds), and DNA (in phosphodiester bonds).

Polyethylene or polythene (IUPAC name polyethene or poly(methylene)) is the most common plastic. The annual global production is approximately 80 million tonnes. Its primary use is in packaging (plastic bag, plastic films, geomembranes, containers including bottles, etc.). Many kinds of polyethylene are known, with most having the chemical formula (C₂H₄)_nH₂

→ Neoprene

Also lenown as poly chloroprene

Synthesis :
Question 4
1 / -0

A cationic colloidal electrolyte forms micelle at $10^{-4} \mathrm{M}$ concentration in water. If $1 \mathrm{mm}^{3}$ solution contains $10^{12}$ micelle structure, then the no. of cations involved in one micelle are $\mathrm{NA}=6 \times 10^{23}$

A
20

B
40

C
60

D
80

Solution

No. of particles of cationic colloidal electrolyte/litre before micelle formation $=10^{-4}$ $\times 6 \times 10^{23}=6 \times 10^{19}$
: No. of particles of cationic colloidal electrolyte/mm $^{3}=6 \times 10^{19} \times 10^{-6}=6$ $\times 10^{13}$
Number of micelles formed $=10^{12} / \mathrm{mm}^{3}$
$\therefore$ Number of cations in one micelle $=6 \times 10^{13} / 10^{12}=60$
In colloidal and surface chemistry, the critical micelle concentration (CMC) is defined as the concentration of surfactants above which micelles form and all additional surfactants added to the system go to micelles.

The CMC is an important characteristic of a surfactant. Before reaching the CMC, the surface tension changes strongly with the concentration of the surfactant. After reaching the CMC, the surface tension remains relatively constant or changes with a lower slope. The value of the CMC for a given dispersant in a given medium depends on temperature, pressure, and (sometimes strongly) on the presence and concentration of other surface active substances and electrolytes. Micelles only form above critical micelle temperature.
For example, the value of $\mathrm{CMC}$ for sodium dodecyl sulfate in water (no other additives or salts) at $25^{\circ} \mathrm{C}$, atmospheric pressure, is $8 \times 10^{-3} \mathrm{mol} / \mathrm{L}$.
The formation of micelles takes place above a particular temperature called Kraft temperature $\left(T_{k}\right)$ and above a particular concentration called critical micellization concentration (CMC).
Micelles are the cluster or aggregated particles formed by association of colloid in solution.
Hence, the correct option is (C)
Question 5
1 / -0

Place the following alcohols in decreasing order of rate of dehydration with concentrated H₂SO₄ :

1. CH₃CH₂CH(OH)CH₂CH₂CH₃

2. (CH₃)₂C(OH)CH₂CH₂CH₃

3. (CH₃)₂C(OH)CH(CH₃)₂

4. CH₃CH₂CH(OH)CH(CH₃)₂

5. CH₃CH₂CH₂CH₂CH₂CH₂OH

A
3 > 2 > 4 > 5 > 1

B
3 > 2 > 4 > 1 > 5

C
3 > 2 > 1 > 4 > 5

D
3 > 2 > 1 > 5 > 4

Solution

The alcohols (3) and (2) are both 3^o, but alcohol (3) gives a more substituted alkene. Alcohol(4) and (1) are both 2^o, but alcohol (4) can give a more substituted alkene and alcohol (5) is 1^o. Rate of dehydration of alcohols with concentrated H₂SO₄follows the order 3^o > 2^o > 1^o.

Reaction with $H_{2} S O_{4}$ [Dehydration of alcohol]: The elimination of water from a compound is known as dehydration. The order of ease dehydration is Tertiary > Secondary > Primary alcohol. The products of dehydration of alcohols are depended upon the nature of dehydrating agents and temperature.

Alcohol leading to conjugated alkene are dehydrated to a greater extent than those of alcohols leading to nonconjugated alkene. Thus dehydration is in orde

Hence, the correct option is (B)
Question 6
1 / -0

In the synthesis of glycerol from propene, the steps involved are :

A
Allyl chloride and glycerol β-chlorohydrin

B
Glycerol trichloride and glycerol α-chlorohydrin

C
Allyl alocohol and α-chlorohydrin

D
Allyl alcohol and monosodium glycerolate

Solution

Synthesis of glycerol from propene involves following steps

Hence, the correct option is (A)
Question 7
1 / -0

Among the following pair of oxides, which pair cannot be reduced by carbon to give the respective metals ?

A
Fe₂O₃, ZnO

B
PbO, Fe₃O₄

C
Cu₂O, SnO₂

D
CaO, K₂O

Solution

Potassium and calcium are strong reductant, hence their oxides cannot be reduced by carbon.

Smelting-carbon reduction process & Slag formation with fluxesSmelting : The process of extracting a metal in the state of fusion is called smelting. In this process the ore is mixed with carbon, obtained after the above reactions and heated in suitable furnace. A suitable flux is added during the operation to convert the non–fusible gangue to fusible slag. The metallic oxide is reduced by carbon and the metal may be obtained in the molten state or as vapours which are condensed. Metals like tin, zinc or lead are obtained by this process.

$\begin{aligned} \mathrm{SnO}_{2}+2 \mathrm{C} & \rightarrow \mathrm{Sn}+2 \mathrm{CO} \\ \mathrm{ZnO}+\mathrm{C} & \rightarrow \mathrm{Zn}+\mathrm{CO} \\ \mathrm{Fe}_{2} \mathrm{O}_{3}+3 \mathrm{CO} & \rightarrow 2 \mathrm{Fe}+3 \mathrm{CO}_{2} \end{aligned}$

Flux and slag : Flux is a substance that is added during smelting to convert infusible silicons or earthy impurities into fusible material known as slag. Impurities + Flux = Slag. The slag is immiscible with the metal and has a low melting point and density. The slag floats on the metal and protects it from oxidation. It is removed from the furnace through the slag hole. If the impurities in the ore are acidic (SiO₂) in nature, a basic flux e.g., CaO, MgO, FeO etc. are added; and if the impurities are basic (CaO, FeO, etc.) then on acidic flux (SiO₂) is used. The gangue or matrix present in the ore is refractory or non–fusible in nature but it reacts with the flux forming fusible slag which does not mix with the molten metal and forms the upper layer. Slag are usually silicates.

$\mathrm{CaO}+\mathrm{SiO}_{2} \rightarrow \mathrm{CaSiO}_{3}$
Hence, the correct option is (D)
Question 8
1 / -0

The half-life of a radioactive isotope is three hours. If the initial mass of the isotope were 256 g, the mass of it remaining undecayed after 18 hours would be :

A
4.0 g

B
8.0 g

C
12.0 g

D
16.0 g

Solution

$t_{1 / 2}=3$ hours, $n=T / t_{1 / 2}=18 / 3=6$
$\mathrm{N}=\mathrm{N}_{0}\left(\frac{1}{2}\right)^{6}$
$=256 \times \frac{1}{8} \times \frac{1}{8}=4 \mathrm{g}$
$\Rightarrow \mathrm{N}=4.0 \mathrm{gm}$
Hence, the correct option is (A)
Question 9
1 / -0

1.2 g of a salt with its empirical formula K_xH_y(C₂O₄)_z was dissolved in 50 mL of water and its 10 mL portion required 11 mL of a 0.1 M HCl solution to reach the equivalence point. In a separate titration, 15 mL of the stock solution required 20 mL 0.2475 M KOH to reach the equivalence point. Identify the correct option.

A
y = 3x

B
y = 2x

C
y = 4x

D
y = 5x

Solution

For the salt $\mathrm{K}_{\mathrm{x}} \mathrm{H}_{\mathrm{y}}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}$
The charge balance is $x+y=2 z$
$12 \mathrm{g}$ salt $=\frac{1.2}{\mathrm{M}}$ moles salt $\equiv \frac{1.2 \mathrm{x}}{\mathrm{M}}$ moles of $\mathrm{HCl}$
$\Rightarrow \frac{1.2 \mathrm{x}}{\mathrm{M}}=5 \times 1.1 \times 10^{-3}=5.5 \times 10^{-3}$
(i)
$\Rightarrow \frac{1.2 \mathrm{y}}{\mathrm{M}}=20 \times 0.2475 \times \frac{50}{15} \times 10^{-3}$
$\frac{1.2 y}{M}=16.5 \times 10^{-3}$
$\frac{\pi}{T} \Rightarrow \frac{y}{x}=3$
$\therefore \quad y=3 x$
If $x=1, y=3 \& Z=2$
Hence, the correct option is (A)
Question 10
1 / -0

Which of the following will react with water and forms stable hydrate?

A
CHCl₃

B
Cl₃CCHO

C
CCl₄

D
ClCH₂CH₂Cl

Solution

Addition reactions of water to aldehydes and ketonesAddition of water
The addition of water to aldehyde results in the formation of a hydrate.

The formation of hydrate proceeds via a nucleophilic addition mechanism.
I. Water, acting as a nucleophile, is attracted to the partially positive carbon of the carbonyl group, generating an oxonium ion.

II. The oxonium ion liberates a hydrogen ion that is picked up by the oxygen anion in an acid‐base reaction.

Hence, the correct option is (B)