Tag: chemistry

Questions Related to chemistry

The odd one is:

[note: valency is not a criterion]

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. iodine

  2. sulphur

  3. phosphorus

  4. carbon

Show answer
Correct Option: A
Explanation:

Catenation,  chemical linkage into chains of atoms of the same element, occurring only among the atoms of an element that has a valence of at least two and that forms relatively strong bonds with itself. The property is predominant among carbon atoms, significant among sulfur and silicon atoms, and slightly present among germanium, nitrogen, selenium, and tellurium atoms.
here, apart from iodine all other have this property.

Which halogen can be purified by sublimation?

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. $F _2$

  2. $Cl _2$

  3. $Br _2$

  4. $I _2$

Show answer
Correct Option: D
Explanation:

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase..
At room temperature, fluorine and chlorine are gases, bromine is liquid, and iodine is solid. They form diatomic molecules in the pure state. Since, $I _2$ is solid at room temperature. It will be sublimated and remaining can not be sublimated
Hence, options D is correct.

The decreasing order of bond dissociation energy among halogens is:

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. $\mathrm{F}-\mathrm{F} >\mathrm{C}\mathrm{l}$ -$\mathrm{C}\mathrm{l}> \mathrm{B}$r - $\mathrm{B}$r $>I-I$

  2. $\mathrm{C}\mathrm{l}$ -$\mathrm{C}\mathrm{l}> \mathrm{B}$r - $\mathrm{B}$r $>\mathrm{F}-\mathrm{F}>I-I$

  3. $\mathrm{C}\mathrm{l}$ -$\mathrm{C}\mathrm{l}> \mathrm{B}$r - $\mathrm{B}$r $>I-I>\mathrm{F}-\mathrm{F}$

  4. $I-I>\mathrm{F}-\mathrm{F}>\mathrm{C}\mathrm{l}$ -$\mathrm{C}\mathrm{l}> \mathrm{B}$r - $\mathrm{B}$r

Show answer
Correct Option: B
Explanation:

Bond dissociation energy decrease
down the group
But bonds dissociation energy of 
$F _2$ is less than excepted due to 
large repulsion of $e^-$ in $F _2$


Which of the statements is/are true about the reactivity order is $F _2\, >\, Cl _2\, >\, Br _2\, >\, I _2.$
I. Lower the activation energy for the chain initiation step, more reactive is the halogen.
II. Lower the activation energy for the first chain propagation step, more reactive is the halogen.
III. More negative is the overall heat of the reaction $(\Delta H _{\zeta}^{})$ of halogenation of alkane, more reactive is the halogen.
IV. Lower the activation energy for the second chain-propagation step, more reactive is the halogen.

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. (I), (II)

  2. (I), (II), (III)

  3. (II), (III)

  4. (II), (III), (IV)

Show answer
Correct Option: C
Explanation:

There are two factors that determine the reactivity of the halogenation of alkanes.
1. Lesser the positive value of $E _{act}$ of the first chain propagating step, more reactive is the halogen.
2. Higher the negative value of overall heat of reaction $(\Delta H _{\zeta}^{})$ more reactive is the halogen. This explains high reactivity and explosive violence with which $F _2$ reacts with $CH _4$.

Iodine gas turns strach iodide paper :

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. Blue

  2. Red

  3. Colourless

  4. Yellow

Show answer
Correct Option: A
Explanation:

Iodine reacts with starch to produce a blue/black color.

The order of basicity of halides is :

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. $Cl < Br < I < F$

  2. $F < I < Br < Cl$

  3. $I < Br < Cl < F$

  4. $Cl < F < I < Br$

Show answer
Correct Option: C
Explanation:

Base is an electron pair donor. The more available the electrons, the more readily they can be donated to form a new bond to the proton and, and therefore the stronger base. When comparing atoms within the same group of the periodic table, the larger the atom the weaker the H-X bond and the lower the electron density making it a weaker base.

Therefore the order of basicity is $F>Cl>Br>I$

 Essential trace element involved in physiology of thyroid glands :

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. K

  2. Mg

  3. Ni

  4. $I _{2}$

Show answer
Correct Option: D
Explanation:

Iodine's main role in animal biology is as constituents of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). These are made from addition condensation products of the amino acid tyrosine, and are stored prior to release in an iodine-containing protein called thyroglobulin. T4 and T3 contain four and three atoms of iodine per molecule, respectively. The thyroid gland actively absorbs iodine from the blood to make and release these hormones into the blood, actions which are regulated by a second hormone TSH from the pituitary. Thyroid hormones are phylogenetically very old molecules which are synthesized by most multicellular organisms, and which even have some effect on unicellular organisms.

Iodine reacts with hot NaOH solution giving the products as-___?

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1.  $NaI$

  2. $ \displaystyle NaIO _{3}$.

  3. A and B

  4. non of these

Show answer
Correct Option: A
Explanation:
Iodine reacts with hot concentrated NaOH solution giving the products sodium iodide (NaI) and  sodium iodate $\displaystyle  (NaIO _3)$.
With cold and dil NaOH, iodine gives sodium hypo iodite $\displaystyle  (NaOI)$

Observe the following statements.
I .Bleaching powder is used in the preparation of chloroform.
II. Bleaching powder decomposes in the presence of $\mathrm{C}\mathrm{o}\mathrm{C}1 _{2}$ to liberate $\mathrm{O} _{2}$.
III. Aqueous $\mathrm{K}\mathrm{H}\mathrm{F} _{2}$ is used in the preparation of fluorine.

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. I,II and III are correct

  2. Only II is correct.

  3. Only I and III are correct

  4. Only I and II are correct.

Show answer
Correct Option: D
Explanation:

Molten $KHF _{2}$ is used in the preparation of fluorine.

Rest two statements are true.

Tincture of iodine contains _____?

group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

  1. $ \displaystyle I _{2}$

  2.  $KI$

  3.  Rectified spirit.

  4. All of these

Show answer
Correct Option: D
Explanation:

Tincture of iodine contains 0.5 ounce iodine,  0.25 ounce KI and 1 pint of rectified spirit.