Chemistry Test - 8

Concept:

• Valency may be defined as the number of electrons that an atom donates or accepts to form the duplet state (i.e., 2 electrons in the outermost shell) or octet state (i.e., 8 electrons in the outermost shell).
• The valency of an element is always a whole number.
• Some elements exhibit more than one valency, i.e., they have variable valency. 
• Valency
  • The outermost electron shell of an atom is called the valence shell.
  • The electrons present in the outermost shell of an atom are called valence electrons.
  • The valence electron of an atom takes part in a chemical reaction because they have more energy than all the inner electrons.
  • The combining capacity of an atom of an element to form a chemical bond is called its valency.

Explanation:

• There are four atomic orbitals namely s,p,d and f and electrons are distributed among these orbitals only.
• Sulphur comes in 3rd period of the periodic table and it contains s, p and d orbital only.
• In the ground state, the d orbital remains empty, when excitation occurs there is jumping of paired electrons to the d orbital and therefore they show an increase in valency or variable valency.
• Sulphur shows a valency of 2, 4 and 6. For example, it forms a compound such as H₂S (valency 2), SO₂ (valency 4) and SO₃ (valency 6).

The correct option is the presence of d orbital in sulphur.

Explanation:

Electron affinity is a measure of the attraction between the incoming electron and the nucleus - the stronger the attraction, the more energy is released.

The factors which affect this attraction are exactly the same as those relating to ionization energies - nuclear charge, distance, and screening.

Now, if a reaction is exothermic, the change in energy is negative. This means that the electron affinity is positive.

Additional Information As we know, the first electron affinities can be negative, positive, or zero. Second electron affinities are always positive.

Og - + e- →O2-(g) - E (ΔH = +ve, Endoenergic) 

When O⁻ changes to O²⁻ change is endothermic because O⁻ repels the incoming electron due to a similar charge, hence, it needs the energy to accept the electron. The second electron affinity of oxygen is

particularly high because the electron is being forced into a small, very electron-dense space. So, electron affinity is positive.

So, we can say that electron affinity is positive when O⁻ changes into O²⁻,

 Important PointsIn general, exceptions arise when new subshells are being filled/half-filled, or in cases where the atom is too small. In the first case, Be and Mg are interesting examples; they have a positive electron affinity

because of the energy difference between the s and p subshells.

The correct answer is Sulphur dioxide.

Explanation:

• The chemical formula of sulphurous acid is H₂SO₃.
• Sulphurous acid is an aqueous solution of water and sulphur dioxide that is typically a dibasic or weak acid. It is colourless and has a strong odour.
• The formation of sulphurous acid involves sulphur dioxide (SO₂). 
• When sulphur dioxide is dissolved in water, it forms an acidic solution. This has long been referred to as a sulphurous acid, H₂SO₃, solution.
• Sulfurous acids, in particular, are critical to the chemical industry.
• Structure of sulphurous acid:

Explanation:

Oxygen gas is prepared by fractional distillation of air. During this process, dinitrogen with less boiling point (78 K) distills as vapors while dioxygen with a higher boiling point (90 K) remains in the liquid state and can be separated.

Explanation:

The formula of formal charge, = V - N - B/2

Where,

V is the number of valence electrons of the neutral atom in isolation (in its ground state);

N is the number of non-bonding valence electrons on this atom in the molecule, and

B is the total number of electrons shared in bonds with other atoms in the molecule.

The atoms have been numbered as 1, 2, and 3. The formal charge on:
The central O atom marked 1:

= 6 - 2 - (6) × 1/2 = + 1

The end O atom marked 3:

= 6 - 4 - (4) × 1/2 = 0

The end O atom marked 2:

= 6 - 6 - (2) × 1/2 = - 1

Explanation:

On going down the group thermal stability order for H₂E  decreases, because H-EH-E bond energy decreases

Hence, the order of stability would be

H₂Po2Te 2Se 2S 2O

Option 4 is NOT correct.

• Sulphur (S), Selenium (Se), and Tellurium (Te) react with Oxygen to form dioxides as well as trioxides depending upon the condition provided.
• Reducing properties of dioxides decreases down the group.
• There is the presence of pπ–pπ bonds in the dioxide molecules, which become weaker with an increase in atomic number.
• This is because, the increase in atomic no. increases size along with a group leads to an increase in the bond length and so the reducing character decreases down the group.
• SO₂ is a reducing agent while TeO₂ is an oxidizing agent.
• Sulphur can show higher oxidation states of +6 whereas, in the case of Tellurium (Te), it is a heavy element lying in the lower part of a group and due to this, it experiences inert pair effect, thereby reluctant to donate its electron for bonding hence exhibiting low oxidation state.
• Down the group, the shielding effect is poor and electron are held strongly by the nucleus.

Explanation:

Among all the four, only KO ₂ has unpaired electrons in it.

→ NO2+ = 5 + 6 × (2) -1 = 16ē

→ AlO2- = 3 + 6 × (2) + 1 = 16 ē

→ BaO2 = 2 + 6 × (2) = 14ē

→  KO2 = 1 + 6 × (2) = 13ē
If you notice the number of electrons present in all the molecules, all have even number of electrons, except KO₂

Explanation - 

• Any chemical molecule in which two oxygen atoms are linked together by a single covalent bond is known as peroxide linkage.

• Out of the given four molecules, only \(H_2S_2O_8\) is having -O-O- linkage.
  • Two oxygen atoms are joined together by a single covalent bond. 

Hence, the correct answer to this question is - \(H_2S_2O_8\)

Concept:

Oxoacids are basically the acids that contain oxygen. Sulphur is known to form many oxoacids. In oxoacids of sulphur, Sulphur exhibits a tetrahedral structure when coordinated to oxygen. Generally, oxoacids of sulphur contain at least one S=O bond and one S-OH bond. Terminal peroxide groups, terminal S=S, terminal and bridging oxygen atoms and chains of (-S-)_n are also observed in addition to S=S and S-OH.

H₂S₂O₃ is called as Thiosulfuric acid. The oxidation number is −2 (for the terminal sulphur), +6 (for the central atom). Since sulphur contains bond between sulphur atoms.

H₂S₂O₄ is called as Dithionous acid. The oxidation number is +3 and the structure has two sulphur bonding between each other.

H₂S₄O₆ is called as polythionic acid. The oxidation number is 0 (for the bridging S atoms), +5 (for the terminal central S atoms). It also contains sulphur bond between them.

H₂S₂O₇ does not show bonding between sulphur atoms.

Pyrosulphuric acid (H₂S₂O₇) is also known as oleum. It is an anhydride of sulphuric acid, it is a colourless, crystalline solid and has a melting point of 36°C. It can be prepared by reacting excess sulphur trioxide with sulphuric acid. The reaction goes like this:

H₂SO₄ + SO₃ → H₂S₂O₇

It reacts with bases to form salts which are called pyrosulphates.

Pyro sulphuric acid (H₂S₂O₇) is a strong acid which is a main constituent of fuming sulfuric acid (oleum). It is also commonly known as disulphuric acid.