RBSE Solutions for Class 9 Science Chapter 4 Chemical Bond and Chemical Equation are part of RBSE Solutions for Class 9 Science. Here we have given Rajasthan Board RBSE Class 9 Science Chapter 4 Chemical Bond and Chemical Equation.
Board | RBSE |
Textbook | SIERT, Rajasthan |
Class | Class 9 |
Subject | Science |
Chapter | Chapter 4 |
Chapter Name | Chemical Bond and Chemical Equation |
Number of Questions Solved | 63 |
Category | RBSE Solutions |
Rajasthan Board RBSE Class 9 Science Chapter 4 Chemical Bond and Chemical Equation
Chemical Bond and Chemical Equation Textbook Questions Solved
Objective Type Questions
Question 1.
Symbol of Na is:
(A) S
(B) Si
(C) Na
(D) Ni
Answer: C
Question 2.
The formula of carbonate radical is:
(A) CO2
(B) CO32-
(C) CO31-
(D) CO
Answer: B
Question 3.
The chemical bond present in sodium chloride is:
(A) Ionic
(B) covalent
(C) Metallic
(D) Hydrogen
Answer: A
Question 4.
In the following, which element shows variable valency?
(A) Na
(B) Ca
(C) K
(D) Cu
Answer: D
Question 5.
Formula of calcium oxide is:
(A) Ca2O2
(B) CaO2
(C) CaO
(D) Ca2 O
Answer: C
Question 6.
The inventor of the modem system of symbol for the elements is:
(A) Berzelius
(B) John Dalton
(C) Rutherford
(D) Neils Bohr
Answer: A
Question 7.
Which molecule in the following has covalent bond?
(A) H2O
(B) NaCl
(C) CaO
(D) CaCO3
Answer: A
Question 8.
Fe is the symbol of:
(A) Iron
(B) Copper
(C) Gold
(D) Silver
Answer: A
Chemical Bond and Chemical Equation Very Short Answer Type Questions
Question 9.
What are the radicals?
Answer
Radicals: A radical is an atom or group of atoms of the same or different elements carrying either positive or negative charge, which behaves as one unit in a chemical reaction.
The positively charged ions are called basic radicals, e.g. sodium Nay Ammonium NH4 .The negatively charged ions are called acid radicals e.g., Nitrate NO3 Oxide, O2; carbonate, CO3 2.
Question 10.
Define the ionic bond.
Answer
Ionic or Electrovalent bond: Ionic bond is formed between the atoms of the electropositive element and electronegative element. When an electropositive element comes close to the electronegative element, the atoms of electropositive element donates electron from its outermost shell and attains the structure of nearest inert gas and becomes positively charged. The electronegative element accepts electron(s) in outermost shell and attains the electron configuration of nearest inert gas. It becomes negatively charged. These oppositely charged ions bind each other, by a strong electrostatic force known as an electrovalent bond or ionic bond.
Question 11.
Write the Latin name and symbol of potassium.
Answer
Latin Name-Kalium, Symbol – K.
Question 12.
Define molecular formula.
Answer
The formula which shows the actual number of atoms of the elements present in one molecule of a substance is molecular formula.
Question 13.
Write the formula of calcium carbonate.
Answer
CaCO3
Question 14.
Write the name of a negative acidic radical having tri-valency.
Answer
Phosphate (PO4)-3.
Question 15.
What is an anion?
Answer
When an atom receives electrons, it carries a negative charge. It is called an anion. Energy is released in the formation of the anion.
Question 16.
Define valency. Give its one example.
Answer
Valency: Valency is defined as the number of hydrogen atoms which combine directly or indirectly with one atom of an element.
Example: One atom of nitrogen combines with three atoms of hydrogen to form ammonia gas. So, the valency of nitrogen is 3.
Chemical Bond and Chemical Equation Short Answer Type Questions
Question 17.
Why is cation smaller than its corresponding atom?
Answer
Atoms of the metals form cations after losing one or more electrons. When a neutral metal atom will lose electrons, the number of electrons will be less than the protons. As a result, forces of attraction will increase between the positively charged nucleus and electrons and the cloud of electrons will contract. This results in the smaller size of cation than the corresponding atom. Also, when the cation is formed by losim electrons of the outermost shell, it has one shell less than the atom and so its size is smaller.
Question 18.
What is variable valency? Explain with an example,
Answer
Some elements possess more than one valence. Such elements are said to possess variable valency. For example, iron has two electrons in its outermost shell (valence shell). On donating these electrons, its valency becomes 2. However, under specific experimental conditions, it can lose another electron from the shell next to valence shell. In such a case, the ion formed has 3 electropositive valencies. In short, iron exhibits two valencies 2 and 3. The Latin name of iron is Ferrum. For lower valency, it is written as Ferrous and the symbol is Fe2+. For higher valency, it is written as Ferric and the symbol is Fe3+.
Question 19.
What is a co-ordinate bond? Explain with an example.
Answer
Co-ordinate bond is that covalent bond which is formed by two atoms sharing a pair of electrons in which both electrons come from the same atom. It is also called a dative covalent bond.
Question 20.
Explain ionization energy.
Answer
The amount of energy required to remove the most loosely bound electron, the valence electron, of an isolated gaseous atom to form a cation is called ionization energy.
Question 21.
Explain the double bond and triple bond with examples.
Answer
Two oxygen atoms may achieve stability by forming covalent bonds with one another. Each oxygen atom has six electrons in its outer shell. To become stable, the two atoms share two pairs of electrons, forming molecular oxygen. When two pairs of electrons are shared (0=0), the bond is called the double covalent bond. Some atoms form triple bonds with one another by sharing three pairs of electrons. For example, nitrogen form a triple covalent bond, by sharing three pairs of electrons with another
Chemical Bond and Chemical Equation Long Answer Type Questions
Question 22.
Explain the differences between covalent compound and an ionic compound.
Answer
Differences between the covalent compound and ionic compound are:
Covalent compounds | Ionic compounds |
Covalent compounds are generally gaseous or volatile liquids. A few exceptions like diamond and graphite are there, which are solids. | Ionic compounds are generally solids. However, mercury is exceptionally a liquid. |
The molecules of covalent compound ! are held by weak forces. So very small; the amount of energy is required to break bonds between two or more molecules. Hence, their melting and boiling points are low. | There is the strong electrostatic force which binds the oppositely charged ions. As a lot of energy is required to break strong electrostatic forces, so ionic compounds have very high melting and boiling points. |
Covalent compounds do not dissociate into positive and negative ions. Thus, when an electric current is applied no ions migrate to opposite poles and hence, no conduction of electric current takes place. | The water on account of its very high energy of solvation weakens the electrostatic forces and hence, breaks the ionic compound into positively and negatively charged ions. These ions easily migrate towards anode and cathode, with the result that aqueous solution of ionic compound conducts electricity. |
Covalent compounds are insoluble in polar liquids (e.g., water). But they are soluble in non-polar liquids such as carbon tetrachloride, benzene etc. | Ionic compounds are generally soluble in polar liquids (e.g., water), but insoluble in non-polar liquids (e.g., CCl4, Benzene, etc.) |
The reactions of covalent compounds are very slow | The reaction of ionic compounds is very fast. |
Most of the covalent compounds have a density less than that of water. It is because molecules of covalent compounds are held by weak forces. Thus there is large intermolecular space | Ionic compounds generally have a higher density than water. This is because ions are held together by strong electrostatic forces of attraction. These ions are fixed at a place having very small interparticle distances. |
Question 23.
Write the molecular formula of the following:
(a) Sodium Carbonate
(b) Zinc Sulphide Ferric
(c) Aluminum Oxide
(d) Sulphate Magnesium
(e) Barium Chloride
Answer
Question 24.
Balance the equations
Answer
Chemical Bond and Chemical Equation Additional Questions Solved
Multiple Choice Questions (MCQs)
Question 1.
Which scientist gave the method to get gold from mercury?
(A) Nagarjuna
(B) Berzelius
(C) Dalton
(D) Rutherford
Answer: D
Question 2.
The radical of phosphate among the following radicals is.
(A) PO42-
(B) PO43-
(C) PO24
(D) PO22-–
Answer: B
Question 3.
The molecular formula of magnesium nitrate is-
(A) Mg(NO3)2
(B) MgNO3
(C) Mg2(NO3)3
(D) Mg(NO3)3
Answer: A
Question 4.
The group of elements showing variable valency is-
(A) Fe,Zn
(B) Mg,Cu
(C) Fe,Cu
(D) Na,K
Answer: C
Question 5.
The formula of the compound obtained by the combination of NH4 and Cl will be-
(A) NH4Cl4
(B) NH4Cl
(C) (NH4)2Cl
(D) NH4Cl2
Answer: B
Question 6.
An ionic bond is formed
(A) By giving and taking (exchange) of electrons
(B) By sharing of electrons
(C) By sharing of electrons on one side
(D) By the pairing of electrons
Answer: A
Question 7.
The element which shows variable valency is-
(A) Calcium
(B) Zinc
(C) Magnesium
(D) Iron
Answer: D
Question 8.
The person who first used the word valency was-
(A) Frankland
(B) Gaber
(C) Berzelius
(D) Priestley
Answer: A
Question 9.
The molecular formula of a metallic chloride is MCI. The molecular formula of its sulphate will be-
(A) MSO4
(B) M(SO4)3
(C) M2SO4
(D) M2(SO4)2
Answer: C
Question 10.
The molecular formed of ferric sulphate is
(A) FeSO4
(B) Fe2(SO4)3
(C) Fe3(SO4)2
(D) Fe2SO4
Answer: B
Chemical Bond and Chemical Equation Very Short Answer Type Questions
Question 1.
Name the elements having the following symbols: Au, Pb, Sn, Mn, Sr, and Si.
Answer
Question 2.
Give one example each of a strong electrolyte and a weak electrolyte.
Answer
Sodium chloride (NaCl) is a strong electrolyte.
Acetic acid (CH3COOH) is a weak electrolyte.
Question 3.
Give one difference between a molecule and a radical.
Answer
The molecule does not carry any charge while a radical carries either a positive charge or a negative charge.
Question 4.
Name any four elements which have variable valency.
Answer
1. Mercury
2. Iron
3. Copper
4. Lead
Question 5.
Write the formula of aluminum sulphate.
Answer
AL3SO4–2 or Al2(SO4)3.
Question 6.
Define a chemical equation.
Answer
The symbolic representation of an actual chemical reaction is called a chemical equation.
Question 7.
What do you mean by a chemical formula?
Answer
A group of symbols of elements which represents one molecule of a substance is called formula.
Example: Formula of water is H2O
Question 8.
What do you understand by molecular formula? Give one example.
Answer
Molecular formula – It is the formula which shows the actual number of atoms of the elements present in one molecule of the substance.
Example: The molecular formula of ammonia gas is NH3. This shows that one molecule of ammonia gas contains one atom of nitrogen and 3 atoms of hydrogen.
Question 9.
Write the formula of magnesium nitride.
Answer
Mg+2N-3 Formula = Mg3N2
Question 10.
Which of the following is trivalent? Sodium, magnesium, and aluminum.
Answer
Aluminum.
Question 11.
Write the symbols for the elements copper, lead, gold, mercury.
Answer
Copper — Cu (from Latin name cuperum)
Lead — Pb (from Latin name plumbum)
Gold — Au (from Latin name aurum)
Mercury — Hg (from Latin name hydrargyrum)
Question 12.
What are polyatomic ions? Give examples.
Answer
The ions which contain more than one atoms behaving as a single unit are called polyatomic ions. For example, po43-, co32-
Chemical Bond and Chemical Equation Short Answer Type Questions
Question 1.
Write the cations and anions present (if any) in the following compounds:
(a) CH3COONa
(b) NaCl
(c) H2
(d) NH4NO3
Answer
(a) CH3COONa
Cation-Na+
Anion- CH3 COO-
(b) NaCl
Cation-Na+
Anion- Cl
(c) H2
Cation – None
Anion – None
(d) NH4NO3
Cation-NH4+
Anion-NO3“
Question 2.
The formula of copper sulphate is CuSO4. What is the valency of copper, if the valency of SO4 is 2?
Answer
This formula suggests that one molecule of copper sulphate contains, an equal number of copper and sulphate ions. Since the valency of the sulphate ion has been given as 2, hence, the copper ion must be of charge 2
∴ Valency of copper is 2.
Question 3.
Give the formulae of the compounds formed from the following sets of elements:
- Calcium and fluorine
- Hydrogen and sulphur
- Nitrogen and hydrogen
- Carbon and chlorine
- Sodium and oxygen
- Carbon and oxygen.
Answer
Question 4.
Define valency of an element. What is the valency of:
(1) Aluminium in aluminium sulphate and
(2) Sodium in sodium sulphate?
Answer
Valency: The combining capacity of an atom of an element is called valency.
- Valency of aluminum in aluminum sulphate [Al2(SO4)3] is 3
- Valency of sodium in sodium sulphate (Na2SO4) is 1.
Question 5.
Find out the valency of the atoms represented by the figure (i) and (ii).
Answer
(1) Its electronic configuration is 2, 8, 8.So, its valency = 0.
(2) Its electronic configuration is 2, 8, 7. So, its valency = 1.
Question 6.
The valency of Cl is 1 and not 7. Give reason.
Answer
Electronic configuration of Cl = 2, 8, 7 (atomic number = 17). Cl needs 1 electron to complete its octet in the valence shell. Therefore, the valency of Cl is 1. The valency of Cl could be 7 only. When it loses 7 electrons from its valence shell. But losing 7 electrons is very difficult than gaining a single electron. Therefore, the agency of Cl is not 7. It is 1.
Question 7.
Write the chemical formulae of the compounds formed by the following ions:
(1) Mg2+ and S2-
(2) Cu2+ and OH
(3) Al3+ and Br
Name the compounds formed in each case.
Answer
Question 8.
Why are ionic compounds hard?
Answer
The reason for hardness is due to the existence of strong electrostatic forces which bind the oppositely charged ions very tightly in a set pattern. Since these charged ions cannot be pulled apart easily, so ionic compounds are hard.
Question 9.
Why are ionic compounds brittle?
Answer
If an external force is applied to ionic compounds the layers of ions will slip over one another and ions of the same nature come near one another in one line. As a result, a strong repulsive force acts between them, so the ionic compound is brittle, as they may break.
Question 10.
What is an acidic radical?
Answer
The non-metallic ions obtained from acids, bases or salts, i.e. from electrolytes, on ionisation in their aqueous solution are called acidic radicals. On ionisation of sodium chloride, chloride ion. CT is obtained which is an acid radical.
Some common acidic radicals are chloride, Cl–, hydroxide, OH-1, nitrate NO31, oxide, O-2,
carbonate CO-2, sulphate, SO42, phosphate, PO4 3.
Question 11.
Why is anion bigger than its corresponding atom?
Answer
When an atom forms an anion, the number of protons remains the same but the number of electrons becomes more. The repulsive force between the electrons becomes more than the attraction of the positively charged nucleus and as a result, the electron cloud of the anion spreads and the electrons become bigger in size.
Question 12.
Write the formulae of the following: Ammonium sulphate, Aluminium carbonate, and Stannous sulphite.
Answer
Chemical Bond and Chemical Equation Long Answer Type Questions
Question 1.
(A) Write the number of atoms present in
(a) SO2 molecule
(b) SO42-
(B) Write down the chemical formulae of
(a) Magnesium nitride
(b) Calcium nitrate
(c) Sodium nitrite
Answer
(A) (a) Three (b) Five
Question 2.
What is a chemical equation? Mention the characteristics and limitations of a chemical equation.
Answer
The symbolic representation of chemical reaction is called a chemical equation.
Characteristics:
A chemical equation conveys many informations as described below:
- It tells about the names of the reactants and products of a chemical reaction.
- It expresses the number of molecules of reactants and products.
- It expresses the relative weights of the reactants and the products.
- It expresses the volumes of the gaseous reactants and products.
Example:
Ammonia gas is formed by the combination of nitrogen and hydrogen, its chemical equation representing the reaction is:
N2 + 3H2→ 2NH3
(14 x 2) + 3 (1 x 2) = 2(14 +1×3)
The above equation expresses that:
1. Nitrogen combines with hydrogen to form ammonia.
2. One molecule of nitrogen combines with three molecules of hydrogen to form two molecules of ammonia.
3. 28 parts by weight of nitrogen have combined with 6 parts by weight of hydrogen to form 34 parts by weight of ammonia.
4. One volume of nitrogen and three volumes of hydrogen combine together to give two volumes of ammonia.
Limitations of a chemical equation:
1. A chemical equation does not always give an idea about the physical state of the reactants and products, whether these are solid, liquid or gas.
2. A chemical equation does not always indicate the conditions necessary for the reaction (i.e. temperature, pressure, the presence of a catalyst).
3. It does not give any idea about the rate of the reaction, whether it is slow or fast.
4. An equation fails to give any indication whether heat is evolved or absorbed.
5. It does not give any idea about the concentration of the reactants.
6. It fails to give any idea about the j mechanism of the reaction.
7. The above equation does not give any indication about the nature of the reaction, whether it is reversible or irreversible.
Question 3.
What is the meaning of the chemical formula of a compound? What information do we get from the formula? Write your answer by giving a suitable example.
Answer
The chemical or molecular formula of a substance represents the actual number of atoms of elements present in one molecule of that substance, in terms of symbols, e.g. formula of sodium chloride is NaCl, acetic acid is C2H4O2
A formula gives the following information:
(a) Formula represents 1 mole of the substance. For example, NaCl represents one mole or 02 x 1023 molecules of sodium chloride.
(b) The formula gives the name of all the elements present in the molecule. For example, elements in Na2SO4 are sodium (Na), sulphur (S), and oxygen (O).
(c) The formula gives information about the number of atoms of elements present in one molecule e.g. Na2SO4 tells that there are two-mole atoms of sodium (Na), a one-mole atom of sulphur (S) and four-mole atoms of oxygen (O) in the molecule.
(d) Molecular formula represents one gram molecular weight or molar mass of the substance. Atomic masses of sodium, sulphur and oxygen are 23, 32 and 16 respectively, so the molecular weight or molar mass of sodium sulphate (Na2SO4) is-
(23 x 2) + 32 + (16 x 4)
= 46 + 32 + 64 = 142
Also, the elements sodium, sulphur, and oxygen are present in the compound in the simplest ratio
23: 16: 8 parts by weight.
Question 4.
Explain symbols and chemical formulae. Differentiate between empirical formula and molecular formula with examples.
Answer
Symbols: In 1813, Berzelius gave a system to represent the element by symbols. A symbol is the shortest form of representing an element. A symbol is a letter or a group of letters of English alphabet which represent an atom of an element.
1. Generally, the first letter of the English name of the element is used as its symbol, e.g.
For example:
Name of the element Symbol
Hydrogen H
Oxygen O
Nitrogen N
Carbon C
Phosphorous P
Sulphur S
2. If there is more than one element which has the first letter in the name common, one small prominent letter in pronunciation is used in addition to the first capital letter.
For example:
Name of the element Symbol
Carbon C
Calcium Ca
Chlorine Cl
Chromium Cr
Cadmium Cd
3. In some cases, the symbols have been derived from the Latin names of the elements.
For example:
|
The significance of symbol:
- A symbol is the shortest form of the name of an element.
- It denotes an atom of the element. For example, O means one atom of oxygen 2C means two atoms of carbon.
- It also represents the atomic weight of that element.
For example, 2H, 12C and 32S mean that atomic weights of hydrogen, carbon and sulphur are 1, 12, and 32 units, respectively. - Formula: Formula is a short name of any element or compound. A group of symbols of elements which represents one molecule of any element or compound is called formula.
For example, the formula of chlorine is Cl2. The formula of common salt is NaCl.
The significance of the formula:
- Formula represents one molecule of the substance. For example, NaCl represents one molecule of sodium chloride.
- The formula gives the name of all constituent elements present in the molecule. For example, constituent elements of Na2SO4 are sodium (Na), one atom of sulphur (S) and oxygen (O).
- The formula gives information about the number of atoms of elements present in one molecule e.g., Na2SO4 tells that there are two atoms of sodium (Na), one atom of sulphur (s) and four atoms of
Oxygen (O). - If atomic weights are known, the molecular weight of the substance can be found. For example, atomic weights of sodium, sulphur and oxygen are 23, 32 and 16 respectively, so the molecular weight of sodium sulphate (Na2SO4) is
23 x 2 + 32 + 16 x 4
= 46 + 32 + 64 = 142. - The number written at the beginning of a formula denotes the number of molecules. For example, in the formula (CuSO4 . 5H2O) of copper sulphate molecule, there are 5 molecules of water (HaO).
Difference between empirical formula and molecular formula:
Empirical formula represents only the simple ratio of the number of atoms of elements in its molecule. For example, the empirical formula of acetic acid is CH2O. It means in the molecule of acetic acid the ratio of atoms of carbon, hydrogen and oxygen is 1: 2: 1. While molecular formula represents the exact number of various constituent elements in a molecule of that compound.
For example, the molecular formula of acetic acid is C2H4O2 which shows that a molecule of acetic acid contains 2 atoms of carbon 4 atoms of hydrogen and 2 atoms of oxygen.
Question 5.
Balance the following chemical equations:
(1) NaOH + Cl2→ NaCl + H2O + NaOCl
(2) NaOH + Cl2→ NaClO3 + NaCl + H2O
(3) Cu + HNO3→ Cu(NO3)2 + NO2 + H2O
(4) Cu + HNO3→Cu(NO3)2 + NO + H2O
(5) Zn + HNO3→ Zn(NO3)2 + H2O + N2O
(6) KMnO4 + SO2 + H2O→ K2SO4+ MnSO4 + H2SO4
Answer
(1) NaOH + Cl2→ NaCl + H2O+ NaOCl
Here, Let us first balance, Na’ on both sides, then we get an equation.
2NaOH + Cl2→ NaCl + H2O + NaOCl
This is the balanced chemical equation.
(2) NaOH + Cl2→ NaClO3 + NaCl + H2O
Here, on balancing ‘O’ on both sides, by inserting 6 before NaOH, and 3 before, H2O on R.H.S., we get,
6NaOH + Cl2→ NaClO3+ NaCl+ 3H2O
Now, on balancing ‘Cl’ finally, as ‘H’ is balanced on both sides, by inserting 3 before Cl2 in L.H.S. and 5 before NaCl in R.H.S., we get:
6NaOH + 3CL→ NaClO3 + 5NaCl + 3H2O
It has all the atoms of the elements, balanced on both sides. This is a balanced chemical equation.
(3) Cu + HNO3→ Cu(NO3)2 + NO2 + H2O
Let us first balance, ‘H’ and ‘O’ on both sides of the equation by inserting ‘4’ before HNOa in L.H.S. ‘2’ before NO2 and 4 before H2O in R.H.S., we get:
Cu + 4HNO3→Cu(NO3)2 + 2NO2+ 2H2O)
(4) Cu + HNO3→ Cu(NO3)2 + NO + H2O
Let us first balance, ‘H’ and ‘O’ on both sides of the equation, by inserting ‘8’ before HNO3 in L.H.S.; 3 before Cu(NOs)2; 2 before NO and 4 before H2O in R.H.S., respectively, we get:”
Cu + 8HNO3→ 3Cu(NO3)2 + 2NO+ 4H2O
Now, to balance ‘Cu’ on both sides, insert ‘3’ before Cu in L.H.S., we get:
3 Cu + 8HNO3→3Cu(NO3)2 + 2NO + 4H2O
(5) Zn + HNOs→ Zn(NO3)2 + H2O + N2O
Let us first balance, ‘H’ and ‘O’ on both sides of the equation by inserting 2 before ‘KMnO4’ in L.H.S., before HNO3 in L.H.S. and 4 before Zn(NO3)2 and 5 before ‘H2O’ in R.H.S. respectively, we get,
4Zn + 10HNO3→ 4Zn(NO3)2 + N2O+ 5H2O
(6) KMnO4 + SO2 + H2O→ K2SO4+ MnSO4 + H2SO4
This equation can be balanced by first balancing ‘O’ and ‘H’ atoms and then ‘K’ and ‘Mn’ atoms, respectively. Similarly as in previous equations, to get the balanced equation as:
2KMnO4 + 5SO2 + 2H2O→ K2SO4 +2MnSO4 + 2H2SO4
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