Chemistry MCQ Quiz - Objective Question with Answer for Chemistry - Download Free PDF

Concept:

Wilkinson's catalyst is an σ –bonded organometallic compound [(Ph₃P)₃ RhCl]. It is commercially used for hydrogenation of alkenes and vegetable oils (unsaturated).

Concept:

EAN rule:

• EAN rule is given by Sidgwick.
• According to the EAN rule, the EAN of metal is equal to the sum of electrons on metal and the electrons donated by the ligands and the EAN is equal to the atomic number of the next noble gas.
• EAN rule is applicable to organometallic complexes. The rule is similar to the 18 electron rule.
• According to this rule, the sum of valence electrons of transition metals or metal ions is equal to 18.
• The complexes in which the EAN rule is followed are considered stable.
• The first row of transition metal carbonyls mostly obeys the 18-electron rule.
• There are many complexes that do not follow the 18 electron rule. 
• These are complexes formed by the transition metals which lie on the left of the periodic table.

Explanation:

Mn2(CO)10

• Manganese in the complex has an oxidation state zero.
• Carbonyl is a neutral ligand with the contribution of two electrons from each unit.
• The contribution from manganese is 7 electrons.
• The contribution from the Mn-Mn bond is 1 electron.
• So, the total contribution from the ligands and metals are:

7 + 1 + 2 × 5 = 18

• Hence, the molecule obeys the 18 electron rule.

Cr(CO)6

​

• The contribution from chromium is 6 electrons.
• Contribution from 6 carbonyl ligands is 6 × 2 = 12.
• Hence, the total number of outermost electrons is 12 + 6 = 18.
• Hence, the molecule obeys the 18 electron rule.

V(CO)6

• The contribution from vanadium is 5 electrons.
• Contribution from 6 carbonyl ligands is 6 × 2 = 12.
• Hence, the total number of outermost electrons is 12 + 5 = 17.
• Hence, the molecule does not obey the 18 electron rule.

Fe(CO)₅

• The contribution from iron is 8 electrons.
• Contribution from 5 carbonyl ligands is 5 × 2 = 10.
• Hence, the total number of outermost electrons is 10 + 8 = 18.
• Hence, the molecule obeys the 18 electron rule.

Hence, the molecule that DOES NOT obey the EAN rule is V(CO)6.

Explanation:

Linkage isomers-

• Linkage isomerism arises when an ambidentate ligand is bonded to the central metal atom/ion through either of its two different donor atoms.

Given data and Analysis:

[Pd(C6H5)2(SCN)2] and [Pd(C6H5)2(NCS)2]  

• The compound shows linkage isomerism because the ligand in the compound is an ambidentate ligand that can bond at more than one atomic site.
• i.e., NCS⁻ and SCN⁻

So option 4 is the correct answer.

Additional Information Geometrical isomers-

• Geometrical isomerism is a type of stereoisomerism having the same molecular formula and same structure but differs in the relative arrangement of atoms. Geometrical Isomerism, arises commonly in heteroleptic complexes.
• This type of isomerism arises due to the different possible geometric arrangements for the ligand.

Ionization isomers-

• The compound which gives different ions in the solution, although they have the same composition, is called ionization isomers, and this property is known as ionization isomerism.

Coordination isomers-

→ Coordination isomers are two or more coordination compounds in which the composition within the coordination sphere.

→ There is an interchange of ligands between the metal in the cation and the metal in the anion

Examples of pairs of coordination isomers are:

• Co(NH₃)₆³⁺ Cr(CN)₆^3- and Cr(NH₃)₆³⁺ Co(CN)₄^3-
• Zn(NH₃)₄²⁺ CuCl₄^2- and Cu(NH₃)₄²⁺ ZnCl₄^2-

Concept:

EAN rule: 

• EAN rule is given by Sidgwick.
• According to the EAN rule, the EAN of metal is equal to the sum of electrons on metal and the electrons donated by the ligands and the EAN is equal to the atomic number of the next noble gas.
• EAN rule is applicable to organometallic complexes. The rule is similar to the 18 electron rule.
• According to this rule, the sum of valence electrons of transition metals or metal ions is equal to 18.
• The complexes in which the EAN rule is followed are considered stable.
• The first row of transition metal carbonyls mostly obeys the 18-electron rule.
• There are many complexes that do not follow the 18 electron rule. 
• These are complexes formed by the transition meals which lie on the left of the periodic table.

Explanation:

•  The Effective Atomic Number (EAN) of [A(NH3)6]Cl3 is 33.
• Each ammonia molecule contributes two electrons.
• The contribution from six ammonia molecules is 6 × 2 = 12.
• The oxidation state of the metal is +3.
• Let the atomic number of the metal be 'x'.
• The total number of electrons from the unit [A(NH3)6]³⁺ is:

x + 12 -3 = 33

or, x = 24.

Hence, the atomic number of the element is 24.

Additional Information

• The element with atomic number 24 is Chromium(Cr). Hence, the complex is;  [Cr(NH3)6]Cl3.
• The metal ion has two valencies:
  • The oxidation state or the primary valency.
  • The co-ordination number or the secondary valency.
• The secondary valencies are satisfied by co-ordinating with primary ligands.
• The bond formed by the ligands and the metal ion forms a coordination sphere.
• The coordination sphere is non-ionizable in solution because of the co-ordinate bond between them.
• The oxidation number or primary valency of the metal ion is satisfied by the side ions which form the ionizable sphere.

• 

Concept:

Ligands:

• A metal ion in a complex is surrounded by coordinating ligands anions or negative ends.
• Ligands donate lone pair of electrons to the metal atoms and form coordinate complexes.
• An electric field is produced at the metal ion by the surrounding ligands.
• This electrostatic approach towards the interaction between metals and ligands is known as crystal field theory.
• CFT theory considers the ligands as point charges.
• There is no overlap between the ligand orbitals and metal ion orbitals.
• The number of ligands satisfying the secondary valency is called the coordination number of the metal.
• The number of sites occupied by a ligand around the metal atom is called its coordination number of the ligand.

Classification of ligands:

• Based on the donor and acceptor properties ligands may be classified into the following types:
  • With one or more lone pairs of electrons:
    • No vacant orbitals to receive back donated electrons from the metal, such as aqua, ammine, fluoro.
    • Vacant orbitals that can be used to receive back donated pi electrons from the low oxidation state example carbonyl.
  • Without a lone pair of electrons but with pi bonding electrons example benzene.
• Ligands may be also classified according to the number of coordination sites they occupy around the metal atom.
  •    When a ligand has only one pair of electrons it can only be bonded to metal at just one point and is called a monodentate ligand.
  • When it can occupy two sites, it is called a bidentate ligand.
  • When it occupies three, four, five, and six then it's called tridentate, tetradentate, pentadentate, and hexadentate respectively.
  • It is also known as the denticity of a ligand.

Explanation:    

EDTA:

• EDTA stands for ethylene diamine tetraacetate.
• It is a hexadentate ligand, which means a single molecule can occupy six stereochemical positions around a metal atom.
• Hence, the coordination number of EDTA is six.
• The structure of EDTA is:

​

• As EDTA is a polydentate ligand, it is also a chelating ligand, it contains donor atoms so arranged that they can occupy more than one position around the same metal atom simultaneously in the first sphere of coordination.
• The resulting complexes are called chelates. Example of chelate complexes are:

​

Hence, EDTA has a coordination number is six.

The correct answer is Sodium carbonate.

Explanation:

• Washing soda is a chemical compound with the formula Na₂CO₃, known as sodium carbonate, and it's a salt of carbonic acid.
• Properties of a Washing soda:
  • It is a transparent crystalline solid.
  • It is one of the few metal carbonates which are soluble in water.
  • It is alkaline with a pH level of 11, it turns red litmus to blue.
  • It has detergent properties or cleansing properties because it can remove dirt and grease from dirty clothes, etc.
  • It attacks dirt and grease to form water-soluble products, which are then washed away on rinsing with water. 

Important Points

Some common chemical compounds with their common names are:

K2CO3 or potassium carbonate is known as pearl ash.

• Pearl ash, in ancient times, was created by baking potash in a kiln in order to remove impurities. The remaining fine, white powder was pearl ash.
• Potassium carbonate is an inorganic compound and a white salt which is soluble in water.
• It is mainly used in the production of glass and soap.

Additional Information

The correct answer is Lactic Acid.

Key Points

• Lactic acid is present in Sour milk or curd.
• The sourness of the milk is due to the presence of lactic acid.
• Human beings feel tired due to the accumulation of lactic acid in the muscles.​

Additional Information

 Key Points

• Atomic Mass of the Hydrogen = 1
• Atomic Mass of the oxygen = 16

Explanation:

1 mole of hydrogen = 1gm

1 mole of oxygen = 16gm

Water (H2O) = 2 Hydrogen atoms + 1 Oxygen atom

2 mole of hydrogen = 2gm

1 mole of oxygen = 16 gm

The ratio of the mass of Hydrogen: Ratio of mass of Oxygen =  2/16 = 1/8 

The ratio of the mass of Hydrogen to the mass of Oxygen in water is always 1:8.

• The number of water molecules present is washing soda is 10.
• We know the molecular formula for Washing Soda is Na₂CO₃.10H₂O.
• Recrystallisation of Sodium Carbonate (Na₂CO₃) gives washing soda.
• In a Washing soda, water is present in the form of crystals.

The correct answer is Vermilion.

• Mercury Sulfide is also known as Vermilion.
• It is a chemical compound composed of the chemical elements mercury and sulfur.
• The chemical formula of Mercury sulfide is HgS.
• It is dimorphic with two crystal forms:
  • Red cinnabar
  • Black metacinnabar

Additional Information

• Marsh Gas is the common name of Methane with the formula of CH₄.
• Mohr's Salt is the common name of Ammonium Ferrous Sulphate with the formula of (NH₄)2Fe(SO₄)₂(H₂O)₆.
• Potash Alum is the common name of Potassium Aluminium Sulphate with the formula of KAl(SO₄)₂.

Explanation:

• Calcium hydroxide is sparingly soluble in water producing an alkaline solution known as limewater.
• Calcium Carbonate is a chemical compound found commonly in rocks as minerals and is the main component of pearls and the shells of marine organisms, eggs, etc.
• When carbon dioxide gas is passed through or over limewater, it turns milky due to the formation of calcium carbonate.
• In the chemical reaction it can be shown as :

\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" id="MathJax-Element-1-Frame" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2

• However, when an excess of CO2 ​is passed through this solution, the milkiness disappears. This is due to the formation of calcium bicarbonate which is colorless and soluble in water.

Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">​\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)​\(\rm \underset{Lime\ water}{Ca CO_3} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{Ca(HCO_3)_2 \ (g)}\)Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate\(\rm \underset{Calcium\ Carbonate}{Ca CO_3} \ \ +H_2O+ \ \underset{Carbon \ Dioxide}{CO_2 \ (g) } \ \longrightarrow \ \underset{Calcium \ bi\ Carbonate}{Ca(HCO_3)_2 \ (g)}\)

Additional Information Reaction involved-

CaCO₃ + 2HCl →  CaCl₂ + CO₂ + H₂O

• The evolved gas is carbon dioxide which then passes through lime water and turns it milky.

Ca(OH)₂ + CO₂ → H₂O + CaCO₃  

• Due to formation of these compounds
• when excess CO₂ is passed

CaCO₃ + H₂O + CO₂ →  Ca(HCO₃)₂ 

• Bicarbonate is formed which again clears the solution

Mistake Points

•  Do not confuse Calcium carbonate and calcium bicarbonate.
• One produces white colour while the other makes it colourless.

The correct answer is Double displacement reaction.

Concept:

Chemical reaction:

• It is a process in which one or more substances, the reactants, are converted to one or more different substances, the products.
• A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Explanation:

• Double displacement reaction: 

• It is a chemical reaction in which two compounds react and exchange their ions forming new products. 
• This reaction often results in the formation of an insoluble compound called a precipitate. 
• Such reactions are represented by equations of the following form: A⁺B^- + C⁺D^- → A⁺D^- + B^-C⁺

​In the given chemical reaction: 

NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

The reactants NaCl and AgNO₃ have exchanged their ions to form NaNO3  and AgCl. 

Thus, it is an example of a double displacement reaction.^​

^{Additional Information}

Types of Chemical Reactions:

Combination reaction:

• Two or more elements or compounds combine together to form a single compound.
• Such reactions are represented by equations of the following form:     A + B → AB.

Decomposition reaction:

• The opposite of a combination reaction, a complex molecule breaks down to make simpler ones.
• Such reactions are represented by equations of the following form: AB → A + B.

Displacement reaction:

• One element takes place with another element in the compound.
• Such reactions are represented by equations of the following form: A + BC → AC + B.

Redox reaction:

• It is a reaction in which one species is reduced and the other is oxidized. 
• Reduction means losing Oxygen or gaining hydrogen 
• Oxidation means gaining oxygen or losing hydrogen. 

pH of some common aqueous solutions

• Aluminium (Al) metal reacts with steam to form a metal oxide and hydrogen.
• This reaction can be given as

2Al + 3H₂O (g) → Al₂O₃ + 3H₂ (g)

• Other metals of this type are Iron (Fe) and Zinc (Zn).

• But these metals do not react with either hot or cold water.