Chemistry Class 9 Final Exam Paper Analysis

St. Anthony’s School, Adhikari
Final Examination
Session:- 2022-2023
Date:- 23-02-2023

Class:- IX                                                               Time:- 2 Hrs
Subject:- Chemistry Science Paper – 2           Full Marks:- 80

Answers to this Paper must be written on the paper provided separately.
You will not be allowed to write during the first 15 minutes.
This time is to be spent in reading the question paper.
The time given at the head of this paper is the time allowed for writing the answers.

Section – I [40 Marks]
[Attempt all questions from this section]

(Q1) Complete the following by filling each of the blanks                                                                                                 [10]

(i) The amount of energy involved in the reaction X+Energy → X⁺+ e⁻ is known as the ionization potential of the element X.
(ii) Down the group, electron affinity decreases.
(iii) In general, non-metals are more electronegative than metals.
(iv) On moving from left to right in a given period, the number of shells remains the same.
(v) Across a period, the ionization potential increases.
(vi) The most active metals are present in Groups 1 and 2 of the Periodic Table.
(vii) The modern Periodic Table has 7 (Seven) periods.
(viii) The elements of period 3 are known as typical elements.
(ix) The metallic character decreases in a period as one moves from left to right.
(x) Actinides are the elements from atomic number 89 to 103 and are radioactive.

(Q2) Choose the most appropriate answer                      [10]
(i) In the periodic table, alkali metals are placed in the group
(a) 1         (b) 11           (c) 17           (d) 18
(ii) An alkaline earth metal is
(a) Palarium       (b) Calcium      (c) Lead        (d) Copper
(iii) An element in period 3 whose electron affinity is zero
(a) Neon            (b) Sulphur        (c) Sodium    (d) Argon
(iv) Among the elements given below, the element with the least electronegativity is
(a) Lithium      (b) Carbon        (c) Boron       (d) Fluorine
(v) The number of electrons lost or gained by an atom refers to
(a) Electrovalency (b) Covalency (c) Donation (d) Acceptance
(vi) The capacity of an atom to attract the shared pair of electrons towards itself is called
(a) Electronegativity                (b) Electron affinity 
(c) Sharing of electrons             (d) Electron donation
(vii) Which of the following doesn’t represent oxidation?
(a) Loss of electrons                         (b) Addition of oxygen
(c) Increase in oxidation number      (d) Addition of hydrogen
(ix) To increase the pH value of neutral solution, we should add:-
(a) An acid      (b) An acid salt      (c) An alkali        (d) A salt
(x) The electrolysis of acidified water is an example of:-
(a) Reduction  (b) Oxidation (c) Redox Reaction (d) Synthesis

(Q3) (A) Match the followings:-                                         [05]

Column A

Column B

                            (i) Proton

(a) An alkaline earth metal

(ii) Sodium

               (b) Halogen

(iii) Barium

               (c) An alkali metal

 (iv) Chlorine

            (d) Responsible for nuclear charge

(v) Electron

               (e) Occupied sub-shell

(Ans) (i) d, (ii) (c), (iii) (a), (iv) (b), (v) (e)

(B) Define the following:-                                                   [05]
(i) Typical elements
(Ans) The elements of the third period (Na, Mg, Al, Si, P, S, Cl, Ar) are called the typical elements. Each of these elements represent the general properties of all the elements of its group.
(ii) Rare earths
(Ans) The sixth period has 15 elements with atomic numbers 57 to 71 (La-Lu), beginning with lanthanum. These 15 elements are very much alike chemically and are known as rare earths or lanthanides.
(iii) Bridge elements
(Ans) The elements of second period are called bridge elements because they connect their own group elements with the elements of next group lying diagonally to them in the periodic table e.g., Li (Lithium) and Mg (Magnesium).
(iv) Lone pair
(Ans) Lone pair is defined as the pair of electrons which are not shared by any of the reacting atoms. Lone pair of electrons is actually responsible for its basic nature. Example:-
(a) Water molecule contains 2 lone pairs on oxygen atom.
(b) Ammonia molecule having 1 lone pair on nitrogen atom.
(v) Hydronium ion
(Ans) It is a hydrogen ion in association with a molecule of water. In a water molecule, the oxygen atom has two pairs of unshared electrons. The hydrogen ion does not have any electron in the valence shell. Hence, it shares a pair of electrons from the oxygen atom by means of coordinate valency to form an H₃0⁺ ion.

(Q4) (A) Write the Chemical Equations:-                          [05]
(i) Molten sodium and Chlorine
(Ans) 2Na + Cl₂ → 2 NaCl
(ii) Nitrogen and oxygen, when lightning strikes
(Ans) N₂ + O₂ → 2NO
(iii) Decomposition of potassium nitrate
(Ans) 2KNO₃ → 2KNO₂ + O₂
(iv) Calcium Bicarbonate reacts with dilute hydrochloric acid
(Ans) Ca(HCO₃)₂ + 2HCL → CaCl₂ + 2H₂O + 2CO₂↑
(v) Zinc is heated with sodium hydroxide solution
(Ans) Zn + 2NaOH → Na₂ZnO₂ + H₂↑

(B) Explain the following:-                                                 [05]
(i) Explain why the elements placed in the same group of the periodic table have the same chemical properties?
(Ans) Elements placed in the same group of the periodic table have the same chemical properties because they have the same number of valence electrons in the outermost shell of their atoms.
(ii) Why group IA elements are called alkali metals?
(Ans) Group IA elements are called alkali metals because their hydroxides are soluble in water and form strong bases.
(iii) Why sodium is a metal while sulphur is a non-metal?
(Ans) Sodium has a larger atomic radii and lower ionization potential than sulphur. Hence sodium is a metal while sulphur is a non-metal.
(iv) Alkali metals are good reducing agents?
(Ans) Alkali metals are good reducing agents because alkali metals have one valence electron which they lose to attain stability. Hence, they themselves undergo oxidation causing reduction of others and are good reducing agents.
(v) The reducing power of elements increases as one goes down a group?
(Ans) When an atom loses an electron then the element is said to be a reducing agent. The reducing power of an element depends upon how quickly it can lose electrons. As we move down the group, the effective nuclear charge decrease. Thus tendency to loose electron increases down the group and so the reducing power.

Section – II [40 Marks]
[Attempt any four questions from this section]

(Q5)(A) Write one word or chemical term for the following:-                                                                           [05]
(i) The law that groups elements in family of three.
(Ans) Law of triads
(ii) The law where every 8th element repeats properties.
(Ans) Newland’s Law of Octaves
(iii) The law where repetition of properties varies periodically.
(Ans) Mendeleev’s Periodic Law
(iv) A bond formed by the transfer of electrons.
(Ans) Electrovalent bond
(v) A bond formed by the sharing of electrons.
(Ans) Covalent bond

(B) What is modern periodic law? Name the elements of ‘first transition series.’                                                       [05]
(Ans) The modern periodic law states that, “The properties of elements are the periodic functions of their atomic number”.
Scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc.

(A) Who gave modern periodic law? What is meant by a group in the periodic table?                                           [03]
(Ans) Henry Moseley gave the modern periodic law. Vertical column in a periodic table are called groups.

(B) Which period is the shortest one? In which period maximum number of elements are present?                   [03]
(Ans) The first period is the shortest period in the periodic table as it has only two elements i.e., H and He. The period in which the maximum number of elements are present is 6th and 7th period. They are the longest period of the periodic table as they have 32 elements.

(C) An element Z has atomic number 16. Answer the following questions on Z:                                                  [04]
(i) State the period and group to which Z belongs.
(ii) Is Z a metal or a non-metal?
(iii) State the formula between Z and hydrogen.
(iv) What kind of a compound is this?

(Ans) Electronic configuration of metal Z = 2, 8, 6
(i) 3rd period, group 16th
(ii) Z is a non-metal
(iii) H₂Z
(iv) Covalent compound.

(A) State the factors which affect or influence the atomic size of the elements in a periodic table.                          [05]
(Ans) Factors which affect the atomic size of the elements in a periodic table are :
(i) Magnitude of nuclear charge 
(ii) Number of shells 
(iii) Screening or shielding effect

(B) Arrange the following elements as directed :           [05]
(i) Ar, He, Ne (in increasing order of electron shells)
(ii) Li, F, C, O (in increasing order of electron affinity)
(iii) Cl, Mg, P, Na (in increasing order of atomic size)
(iv) Cl, Li, F, N (in increasing order of electronegativity)
(v) Cl, S, Al, Na (in increasing order of ionisation potential)

(i) He, Ne, Ar 
(ii) Li, C, O, F 
(iii) Cl, P, Mg, Na 
(iv) Li, N, Cl, F 
(v) Cl, S, Al, Na.

(Q8) (A) The combination of atoms to form molecules is based on octet rule. Give two limitations of this rule.    [04]
(Ans) (i) It cannot explain the formation of molecules like BeF2, BF3 in which the central atom has less than 8 electrons in its valence shell.
(ii) It cannot explain the formation of molecules such as PF5, SF6 etc., in which central atom has more than eight electrons in its valence shell.

(B) Write the general characteristics of electrovalent compounds.                                                                        [06]
(Ans) The general characteristics of electrovalent compounds are :
(i) Electrovalent compounds are mostly crystalline in nature.
(ii) Electrovalent compounds form hard crystals. These crystals are usually brittle.
(iii) Electrovalent compounds have high density with high melting and boiling points.
(iv) Electrovalent compounds are soluble in polar solvents.
(v) Electrovalent compounds exhibit isomorphism.
(vi) They react very fast.

(Q9) (A) On what factors the formation of an electrovalent compound depends?                                                         [04]
(Ans) The formation of an ionic or electrovalent compound depends on the following factors
(i) Low ionisation energy : Lesser is the ionisation energy of an atom, greater will be its tendency to form cation by losing the valence electron. Metals with lower ionisation energy values have a greater tendency to form ionic bonds.
(ii) High electron affinity : Higher the value of electron affinity, greater will be the tendency of the atom to gain electron and form an anion. Elements with high electron affinity values form ionic compounds.
(iii) High Electronegativity difference : Higher the difference in the electronegativities of the elements, easier the transfer of electrons. Hence, more ionic nature of the resulting compound.

(B) Write the important characteristics of covalent compounds.                                                                        [06]
(Ans) The important characteristics of covalent compounds are as follows :
(i) Usually covalent compounds exist in gaseous, liquid or amorphous state.
(ii) Covalent compounds have low melting or boiling points.
(iii) Except for graphite, covalent compounds are bad conductors of electricity.
(iv) Covalent compounds are usually soluble in non-polar solvents (organic solvents). Polar covalent compounds are however soluble in polar solvents.
(v) Covalent compounds undergo reactions slowly.

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