Chemistry: CUET Mock Test - 7 - CUET MCQ

Benzenediazonium salts are stable in cold environment, but readily react with water when the temperature increases even slightly.

Benzenediazonium chloride is readily soluble in polar solvents like water. However, it is less soluble in solvents like alcohol.

Certain diazonium salts such as fluoroborates are insoluble in water. This makes them stable enough to be dried and stored.

Diazonium salts are unstable and may explode in dry state. Therefore, they are generally used in solution or aqueous state.

Benzenediazonium chloride is usually obtained in crystal form. It is unstable and formed for a short period when aniline reacts with nitrous acid. It is a salt with chlorine as the negative group and diazo group as positive.

Benzenediazonium bromide is a salt, made of a positive diazonium group and a negative bromide ion. Thus, it remains neutral to litmus paper.

Polarity occurs between two entities when there is a difference in the magnitude and signs of charges between the two entities. In this case, the halogen is more negatively charged than the carbon, and hence it is polarised.

Iodine lies below bromine, chlorine and fluorine in the halogen group and hence has the largest atomic size.

Since the C-F bond length will be shorter than the C-Cl bond length due to the smaller size of F atom, it will require more energy to break the C-F bond, hence the enthalpy value of C-Cl bond will be lower than that of C-F bond.

The size of Cl atom is smaller than the size of Br atom as the latter appears lower than Cl in the halogen group. Hence, the carbon-halogen bond length of C-Br must be bigger than that of C-Cl, i.e., 178pm, therefore it must be 193pm.

The common trend within the halogen group in the periodic table is that the size of the atom increases from top to bottom.

Synergic bonding is the overall effect of the sigma and pi interactions in metal carbonyl bonds. M-C pi bonds are also known as back bonding.

The coordination number of pentacarbonyliron(0) is 5 as CO is a unidentate ligand and hence its geometry id trigonal bipyramidal.

The pi bond involves donation of electrons from filled metal d orbitals into empty antibonding pi orbitals of CO. This is also called a back bond.

Primary valence of a metal ion is also known as its oxidation number. The secondary valence is equal to coordination number and it is fixed for a metal. Coordination polyhedra is the term for the spatial arrangements of the groups/ions around the metal.

Werner observed that ‘x’ mol of AgCl was precipitated per mole of CoCl₃.4NH₃ with excess silver nitrate. Currently, there are seven groups attached to the cobalt atom. For the secondary valence to be six, one of the chloride (x = 1) has to be precipitated as AgCl, therefore 1:1 electrolyte.

After the reaction, it will form [Ni(H₂O)₆]^2- and 2Cl^– in which the former is the coordination complex. There are six water molecules bound to Ni, which makes the secondary valence of Ni as 6.

In [Co(H₂O)(CN)(en)₂]²⁺, the overall charge is +2 and 0, -1 and 0 on H₂O, CN and en groups respectively. If ‘x’ is the oxidation number of Co, then (x + 0 – 1 + 0 = +2), which implies x=+3.
Similarly, in [CoBr₂(en)₂]⁺, the charge on Br is -1, so if ‘y’ is the oxidation number of Co, then (y – 2 + 0 = +1), which implies y = +3. Therefore, the sum of the oxidation numbers is 3 + 3 = 6.

This compound, also known as Prussian blue, dissociates into 4 Fe³⁺ and 3[Fe(CN)₆]^4- ions, of which the latter is the coordination entity having a charge of -4.
The Fe atom in question is the one inside the bracket. Since CN has a charge of -1 and there are 6 of them, the primary valence of Fe will be 6 – 4 = +2.

Potassium ferrocyanide, K₄[Fe(CN₆)], is a complex salt that does not dissociate into Fe²⁺ and CN^– ions when dissolved in water. The other three, i.e., potash alum, carnallite and Mohr’s salt are double salt that dissociate into simple ions completely when dissolved in water.

[Fe(CN)₆]^4- is the coordination complex ion of the coordination compound K₄[Fe(CN₆)], or potassium ferrocyanide, which is also a complex salt. Coordination complexes are also known as coordination entities.

Since the secondary valence is 6, the compound should have six groups linked to Pt atom. But it already has six groups linked to it and cannot lose any Cl atoms to form AgCl. Hence, no AgCl will be produced.

Transition metals bond a bit differently from main group elements. They form coordinate covalent bonds and are often the central metal ion/atom of coordination complexes. Thus, octahedral, tetrahedral and square planar shapes are more common in transition metal central atoms.

In coordination compounds, the ions outside the square brackets are called counter ions, and the species within the square bracket are the coordination entities.

The different compounds of cobalt(III) chloride with ammonia show distinct properties, most notably with respect to colour and conductivity measurements in solution.

Because they are all metals, the transition elements are often called the transition metals. As a group, they display typical metallic properties and are less reactive than the metals in group 1 and group 2 of the periodic table.

The third transition series or 5d series corresponding to the filling of 5d sublevel consists of the following 10 elements of the 6^th period: La (Atomic No. = 57); Hf (Atomic No. = 72), Ta, W, Re, Os, Ir, Pt, Au and Hg (Atomic No. = 80).

The first transition series or 3d series corresponding to the filling of 3d sublevel consists of the following 10 elements of the 4^th period: Sc (Atomic No. = 21), Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn (Atomic No. = 30).

Unlike s or p block elements which are usually discussed as columns or groups, d-block elements are better discussed by classifying them into horizontal series. In the periodic table, there are four main transition series of elements corresponding to filling of 3d, 4d, 5d and 6d sublevels in the 4^th, 5^th, 6^th and 7^th periods.

All transition elements are d-block elements, but all d-block elements are not transition elements. Zinc has the electronic configuration [Ar] 3d¹⁰4s², and the configuration of the Zn²⁺ ion is [Ar] 3d¹⁰. Thus, both the element and its only known stable ion have completely filled d-orbitals. Also, the metal does not exhibit any variable valency or multiple oxidation states in compound formation.