NSEC CHEMISTRY

DAILY CHEMISTRY TEST QUESTIONS

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1 General Principles & Process of Isolation of Metals

Greyish white metal which is a good conductor of electricity and heat and has a boiling point of 920^?C is :

1) aluminium
2) tin
3) iron
4) zinc

Option 1

Option 2

Option 3

Option 4 Solution:

Solution

Greyish white metal which is a good conductor of electricity and heat and has a boiling point of $$920^\circ C$$ is zinc.

2 Purification and Characterisation of Organic Compounds

Styrene can be purified by:

1) Simple distillation

2) Fractional distillation

3) Vacuum distillation

4) Steam distillation

Option 1

Option 2

Option 3 Solution:

SOLUTION

Styrene is primarily a synthetic chemical. It is also known as vinylbenzene,ethenylbenzene, cinnamene or phenylethylene. It's a colorless liquid that evaporates easily and has a sweet smell. Styrene can be purified by Vacuum distillation.

Vacuum distillation is the process of lowering the pressure in the column above the solvent to less than the vapor pressure of the mixture, creating a vacuum, and causing the elements with lower vapor pressures to evaporate off.

Option 4

3 P � Block Elements

Phosphorous occurs as

1. phosphide.
2. phosphate.
3. oxides
4. element (free state).

Option 1

Option 2 Solution:

Option 3

Option 4

4 D and F Block Elements

Anhydrous FeSO4 is

1) brown

2) green

3) white

4) black

Option 1

Option 2

Option 3 Solution:

Option 4

5 Coordination Compounds

Among the following, which are ambidentate ligands?
(i) SCN⁻
(ii) $$NO^-_3$$
(iii) $$NO^-_2$$
(iv) $$C_2O^{2-}_4$$

1) (i) and (iii)
2) (i) and (iv)
3) (ii) and (iii)
4) (ii) and (iv)

Option 1 Solution:

Solution

Ambidentate ligand has two or more donor atoms, but during complex formation, only one donor atom is attached to central metal. SCN− ion has donor atoms N and S. It links to metal as either M−SCN or M−NCS. NO₂⁻ group has donor atoms N and O. It links to metal as either M−ONO or M−NO2.

Option 2

Option 3

Option 4

6 Chemical Kinetics

A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial velocity is ten times the permissible value, after how many days will it be safe to enter the room?

1) 100 days
2) 1000 days
3) .300 days
4) 10 days

Option 1

Option 2 Solution:

Solution

Say Permissible rate is $$\vartheta$$

then $$\vartheta _{2}=100$$

$$\vartheta =kA$$

$$=kA_{0}e^{-kt}$$

$$kA_{0}e^{\frac{-0.693t}{t_{\frac{1}{2}}}}

$$\vartheta =\vartheta _{0}e^{\frac{-0.693t}{t_{\frac{1}{2}}}}$$

$$\vartheta =10\vartheta e^{\frac{-0.693t}{t_{\frac{1}{2}}}}$$

$$l_{n}(10)=\frac{-0.693}{t_{\frac{1}{2}}}t$$

$$t=\frac{t_{\frac{1}{2}}*2.303}{0.693}*10$$

$$=1000$$days

Option 3

Option 4

7 Environmental Chemistry

Which one of these is a neurotoxin that accumulates both in soft tissues and the bones, damaging the nervous system and causing brain disorders?

1) Mg
2) Na
3) K
4) Pb

Option 1

Option 2

Option 3

Option 4 Solution:

Solution

Lead is a neurotoxin that accumulates both in soft tissues and the bones, damaging the nervous system and causing brain disorders.

8 D and F Block Elements

Number of identical Cr-O bonds in dichromate ion Cr₂O₇²⁻ is :

1) 4
2) 6
3) 7
4) 8

Option 1

Option 2 Solution:

Solution

There are '6' identical Cr - O bonds in the dichromate ion Cr₂O₇²⁻

In a dichromate ion Cr₂O₇²⁻, there are 6 terminal Cr – O bonds. All these bonds are equivalent due to resonance.

The Dichromate ions Cr₂O₇²⁻. are oxoanions of chromium in the oxidation state +6.

Option 3

Option 4

9 Alcohols Phenols and Ethers

When 10mL of ethyl alcohol (density =0.7893gmL⁻¹) is mixed with 20 mL of water (density 0.9971 gmL⁻¹) at 25^oC, the final solution has a density of 0.9571gmL⁻¹. The percentage change in total volume on mixing is :

1) 1%
2) 2.4%
3) 3.1%
4) none of these

Option 1

Option 2

Option 3 Solution:

Solution

Mass $$\displaystyle =$$ density $$\displaystyle \times $$ volume

Mass of ethyl aclohol $$\displaystyle = 0.7893 \times 10 = 7.893$$g

Mass of water $$\displaystyle = 0.9971 \times 20 = 19.942$$g

Total mass of solution $$\displaystyle = 7.893 + 19.942 = 27.835$$ g

Volume of solution after mixing $$\displaystyle = \dfrac {Mass}{Density} = \dfrac {27.835}{0.9571}=29.083mL $$

Total volume of ethanol and water before mixing $$\displaystyle = 10 + 20 = 30 mL$$

The percentage change in total volume on mixing is $$\displaystyle = \dfrac {30 - 29.083}{30} \times 100 = 3.1 $$ %.

Option 4

10 Haloalkanes and Haloarenes

Which of the following can yield acetylene in one step?

1) Ethene

2) Ethylene dichloride

3) Sodium acetate

4) Propyne

Option 1

Option 2 Solution:

Ethylene is obtained through dehalogenation while acetylene is obtained thorough a double dehydrohalogenation.

Option 3

Option 4

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