CG SCERT (Chhattisgarh Board) Class 9 Science Solutions | 2026-27 Official Edition
Complete 100% textbook-grounded CG Board Class 9 Science Chapter 9 Solutions: Chemical Formula and Mole Concept (रासायनिक सूत्र और मोल संकल्पना) in Bilingual Format (English & Hindi Medium).
End-of-Chapter Exercises (Solutions)
अभ्यास के सभी प्रश्नों के हल
(i) The molecular weight of CH_3OH is: (a) 32 u (b) 29 u (c)…
(CH_3OH का अणु भार है:)
(i) The molecular weight of CH_3OH is:
(a) 32 u
(b) 29 u
(c) 25 u
(d) 20 u
(ii) Basic radical is:
(a) Positively charged ion /
(b) Negatively charged ion /
(iii) Ions that have a negative charge are:
(a) Positively charged ion /
(c) Acidic radicals /
(iv) The value of Avogadro’s number is:
(a) 6.022 × 1023
(b) 6.022 × 1022
(c) 6.022 × 1024
(d) 60.22 × 1023
(v) The volume of any gas at 0°C and 1 atm pressure (STP) is:
(a) 11.2 litre
(b) 22.4 litre
(c) 100 litre
(d) 33.8 litre
(i) Unit formula mass is used for ……………………………………….. compounds.
–
(ii) The molecular weight of C12H22O11 is ………………………………………….
–
- Step-by-step Calculation: (12 × 12) + (22 × 1) + (11 × 16) = 144 + 22 + 176 = 342 u.
(iii) The number of elements in PO43- is ……………………………………………………
–
- Explanation: Phosphorus (P) and Oxygen (O) are the two distinct elements present.
(iv) The number of atoms in one mole of carbon is ……………………………………….
–
- English:
- Basic Radicals: Positively charged cations obtained upon the ionization of bases (e.g., NaOH → Na^+ + OH^-, where Na^+ is a basic radical).
- Acidic Radicals: Negatively charged anions obtained upon the ionization of acids (e.g., HCl → H^+ + Cl^-, where Cl^- is an acidic radical).
- Hindi:
- English:
Clusters or groups of atoms of different elements that carry a net fixed positive or negative charge and act as a single unit in chemical reactions are called polyatomic ions.
Examples: Ammonium ion (NH4^+), Carbonate ion (CO32-), Sulphate ion (SO42-), Hydroxide ion (OH^-), Nitrate ion (NO3^-).
- Hindi:
| Column A | Column B | Answer / |
|---|---|---|
| (i) Number of atoms in one mole | (i) 14 gram | (v) 6.022 × 1023 |
| (ii) Acidic radical | (ii) Mg2+ | (iii) SO42- |
| (iii) Basic radical | (iii) SO42- | (ii) Mg2+ |
| (iv) The weight of one mole of nitrogen atoms | (iv) 2 mol | (i) 14 gram |
| (v) The number of moles in 88 g of CO2 | (v) 6.022 × 1023 | (iv) 2 mol |
- English:
- Definition: The formula unit mass of an ionic compound is the sum of the atomic masses of all atoms/ions present in its formula unit. It is used for ionic solids that do not exist as discrete molecules.
- Calculation for MgSO4:
- Atomic mass of Magnesium (Mg) = 24 u
- Atomic mass of Sulphur (S) = 32 u
- Atomic mass of Oxygen (O) = 16 u
- Formula unit mass of MgSO4 = 24 + 32 + (4 × 16) = 24 + 32 + 64 = 120 u.
- Hindi:
- MgSO4
If the formula of the carbonate of a metal is M_2CO3, then what will be the formula of its nitrate? / M_2CO3 , ?
If the formula of aluminium sulphate is Al2(SO4)3, then what is the charge on the Al ion and what is the formula of zinc sulphate? / Al2(SO4)3 , Al ?
The ion X has two positive charges on it (X2+). Write the formulae of the nitrate, sulphate and phosphate of X. / X (X2+) X ,
Calculate the molecular weights of the following: PCl5, H_2O2, S8, HCl, NH3. / : PCl5, H_2O2, S8, HCl, NH3
Step-by-step Numerical Solution /
Calculate the number of moles in the following: 12 g of O2, 22 g of CO2. / : 12 g O2, 22 g CO2
**Determine the chemical formulae of the following using the crisscross method:
- Correct Option / : (a) 32 u.
- Step-by-step Calculation:
12 + (3 × 1) + 16 + 1 = 12 + 3 + 16 + 1 = 32 u.
- Correct Option / : (a) Positively charged ion / .
- Correct Option / : (c) Acidic radicals / .
- Correct Option / : (a) 6.022 × 1023.
- Correct Option / : (b) 22.4 litre.
Answer / : 6.022 × 1023.
(v) The mass of one mole of water is …………………………………………
–
Answer / उत्तर:
- क्षारीय मूलक: क्षारों के आयनन से प्राप्त धनावेशित आयनों (धनायनों) को क्षारीय मूलक कहते हैं (जैसे NaOH → Na^+ + OH^-, जहाँ Na^+ क्षारीय मूलक है)।
- अम्लीय मूलक: अम्लों के आयनन से प्राप्त ऋणावेशित आयनों (ऋणायनों) को अम्लीय मूलक कहते हैं (जैसे HCl → H^+ + Cl^-, जहाँ Cl^- अम्लीय मूलक है)।
Answer / उत्तर:
विभिन्न तत्वों के परमाणुओं के ऐसे समूह जिन पर एक निश्चित धनात्मक या ऋणात्मक आवेश होता है तथा जो रासायनिक अभिक्रियाओं में एक इकाई के रूप में कार्य करते हैं, बहुपरमाणुक आयन कहलाते हैं।
उदाहरण: अमोनियम आयन (NH4^+), कार्बोनेट आयन (CO32-), सल्फेट आयन (SO42-), हाइड्रॉक्साइड आयन (OH^-), नाइट्रेट आयन (NO3^-)।
Answer / उत्तर:
- परिभाषा: किसी आयनिक यौगिक का सूत्र इकाई द्रव्यमान उसके सूत्र में उपस्थित सभी परमाणुओं/आयनों के परमाणु द्रव्यमानों का योग होता है। इसका उपयोग उन आयनिक ठोसों के लिए किया जाता है जिनमें पृथक अणु नहीं पाए जाते।
- MgSO4 की गणना:
- मैग्नीशियम (Mg) का परमाणु भार = 24 u
- सल्फेट में सल्फर (S) का परमाणु भार = 32 u
- ऑक्सीजन (O) का परमाणु भार = 16 u
- MgSO4 का सूत्र इकाई द्रव्यमान = 24 + 32 + (4 × 16) = 24 + 32 + 64 = 120 u।
Step-by-step Solution /
- English:
- Carbonate ion is CO32- with a valency of 2.
- In formula M_2CO3, two atoms of metal M combine with one CO32- ion.
- Therefore, valency of metal M is +1 (M^+ ion).
- Nitrate ion is NO3^- with a valency of 1.
- Criss-crossing valency of M^+ (1) and NO3^- (1) yields the formula MNO3.
- Hindi:
Step-by-step Solution /
- English:
- Charge on Al ion: In Al2(SO4)3, SO4 has a charge of -2. Three SO42- ions carry a total charge of -6. For charge balance, two Al ions must carry a total charge of +6. Hence, each Al ion carries a charge of +3 (Al3+).
- Formula of zinc sulphate: Zinc ion is Zn2+ (valency 2) and sulphate ion is SO42- (valency 2). Criss-crossing gives ratio 2:2 which simplifies to 1:1 → Formula: ZnSO4.
- Hindi:
Step-by-step Solution /
- English:
- Given ion: X2+ (Valency = 2)
- Nitrate of X: Nitrate ion is NO3^- (Valency = 1). Criss-crossing valencies yields X(NO3)2.
- Sulphate of X: Sulphate ion is SO42- (Valency = 2). Simplifying 2:2 ratio yields XSO4.
- Phosphate of X: Phosphate ion is PO43- (Valency = 3). Criss-crossing valencies yields X3(PO4)2.
- Hindi:
Step-by-step Numerical Solution /
- English:
- Phosphorus pentachloride (PCl5):
- Atomic mass: P = 31 u, Cl = 35.5 u
- Molecular weight = 31 + (5 × 35.5) = 31 + 177.5 = 208.5 u
- Hydrogen peroxide (H_2O2):
- Atomic mass: H = 1 u, O = 16 u
- Molecular weight = (2 × 1) + (2 × 16) = 2 + 32 = 34 u
- Sulphur molecule (S8):
- Atomic mass: S = 32 u
- Molecular weight = 8 × 32 = 256 u
- Hydrogen chloride (HCl):
- Atomic mass: H = 1 u, Cl = 35.5 u
- Molecular weight = 1 + 35.5 = 36.5 u
- Ammonia (NH3):
- Atomic mass: N = 14 u, H = 1 u
- Molecular weight = 14 + (3 × 1) = 17 u
- Hindi:
- English:
- Formula: Mass (m) = Number of moles (n) × Molar Mass (M)
- 5 moles of Ammonia (NH3):
- M = 17 g/mol ⇒ m = 5 × 17 = 85 g
- 0.5 moles of Water (H_2O):
- M = 18 g/mol ⇒ m = 0.5 × 18 = 9 g
- 1.50 moles of Na^+ ions:
- M = 23 g/mol ⇒ m = 1.50 × 23 = 34.5 g
- 0.2 moles of Oxygen atoms (O):
- M = 16 g/mol ⇒ m = 0.2 × 16 = 3.2 g
- Hindi:
Step-by-step Numerical Solution /
- English:
- Formula: Number of moles (n) = (Given mass (m))/(Molar mass (M))
- 12 g of Oxygen gas (O2):
- Given mass m = 12 g
- Molar mass M = 2 × 16 = 32 g/mol
- n = 12/32 = 3/8 = 0.375 moles
- 22 g of Carbon dioxide (CO2):
- Given mass m = 22 g
- Molar mass M = 12 + (2 × 16) = 44 g/mol
- n = 22/44 = 0.5 moles
- Hindi:
Step-by-step Solution /
- English:
- Iron sulphate (Iron(II) sulphate):
- Positive ion = Fe2+ (valency 2), Negative ion = SO42- (valency 2)
- Ratio 2:2 simplifies to 1:1 → Formula: FeSO4
- (Note: If Iron(III) sulphate is considered, Fe3+ and SO42- → Fe2(SO4)3)
- Copper nitrate (Copper(II) nitrate):
- Positive ion = Cu2+ (valency 2), Negative ion = NO3^- (valency 1)
- Criss-crossing valencies yields → Formula: Cu(NO3)2
- Sodium sulphide:
- Positive ion = Na^+ (valency 1), Negative ion = S2- (valency 2)
- Criss-crossing valencies yields → Formula: Na_2S
- Magnesium hydrogencarbonate:
- Positive ion = Mg2+ (valency 2), Negative ion = HCO3^- (valency 1)
- Criss-crossing valencies yields → Formula: Mg(HCO3)2
- Hindi:
- , Fe3+ SO42- → Fe2(SO4)3)*
If the atomic weight of carbon is 12…
यदि कार्बन का परमाणु भार 12 u है…
If the atomic weight of carbon is 12 u, then what will be the molecular weight of carbon dioxide (CO2)?
- Atomic weight of Carbon (C) = 12 u
- Atomic weight of Oxygen (O) = 16 u
- Molecular weight of CO2 = (Atomic weight of C) + 2 × (Atomic weight of O)
- Molecular weight of CO2 = 12 + (2 × 16) = 12 + 32 = 44 u
If the atomic weight of nitrogen is 14…
यदि नाइट्रोजन का परमाणु भार 14 u है…
If the atomic weight of nitrogen is 14 u, then what is the molecular weight of ammonia (NH3)?
- Atomic weight of Nitrogen (N) = 14 u
- Atomic weight of Hydrogen (H) = 1 u
- Molecular weight of NH3 = 14 + (3 × 1) = 14 + 3 = 17 u
Calculate the molecular weight of hydrogen Hsub2sub
हाइड्रोजन Hsub2sub के अणु भार की गणना कीजिए।…
Calculate the molecular weight of hydrogen (H2).
- Atomic weight of Hydrogen (H) = 1 u
- Molecular weight of H2 = 2 × 1 = 2 u
Calculate the formula unit mass of the following…
निम्नलिखित आयनिक यौगिकों के सूत्र इकाई द्रव्यमान की…
Calculate the formula unit mass of the following ionic compounds: Na_2O, MgCl2, CaCl2, CaO.
- Sodium Oxide (Na_2O)
- Atomic weight of Na = 23 u, O = 16 u
- Formula unit mass = (2 × 23) + 16 = 46 + 16 = 62 u
- Magnesium Chloride (MgCl2)
- Atomic weight of Mg = 24 u, Cl = 35.5 u
- Formula unit mass = 24 + (2 × 35.5) = 24 + 71 = 95 u
- Calcium Chloride (CaCl2)
- Atomic weight of Ca = 40 u, Cl = 35.5 u
- Formula unit mass = 40 + (2 × 35.5) = 40 + 71 = 111 u
- Calcium Oxide (CaO)
- Atomic weight of Ca = 40 u, O = 16 u
- Formula unit mass = 40 + 16 = 56 u
Complete Table 1
Complete Table 1
| Name of Compound | Radicals Present: Positive | Radicals Present: Negative | No. of Charges: Positive | No. of Charges: Negative | Formula of Compound |
|---|---|---|---|---|---|
| Sodium carbonate | Na^+ | CO32- | 1 | 2 | Na_2CO3 |
| Ammonium hydroxide | NH4^+ | OH^- | 1 | 1 | NH_4OH |
| Magnesium carbonate | Mg2+ | CO32- | 2 | 2 | MgCO3 |
| Iron phosphate | Fe2+ | PO43- | 2 | 3 | Fe3(PO4)2 |
Use the crisscross method to write down the…
क्रिसक्रॉस विधि का उपयोग करके निम्नलिखित आयनिक यौगिकों…
Use the criss-cross method to write down the formulae of the following ionic compounds
ammonium chloride, calcium hydroxide, magnesium sulphate, ammonium sulphate, calcium phosphate.
- Ammonium chloride: Ions are NH4^+ (valency 1) and Cl^- (valency 1). Criss-crossing valencies gives ratio 1:1 → Formula: NH_4Cl.
- Calcium hydroxide: Ions are Ca2+ (valency 2) and OH^- (valency 1). Criss-crossing valencies gives ratio 1:2 → Formula: Ca(OH)2.
- Magnesium sulphate: Ions are Mg2+ (valency 2) and SO42- (valency 2). Simplifying ratio 2:2 to 1:1 → Formula: MgSO4.
- Ammonium sulphate: Ions are NH4^+ (valency 1) and SO42- (valency 2). Criss-crossing valencies gives ratio 2:1 → Formula: (NH4)_2SO4.
- Calcium phosphate: Ions are Ca2+ (valency 2) and PO43- (valency 3). Criss-crossing valencies gives ratio 3:2 → Formula: Ca3(PO4)2.
Explain the following reactions using the mole concept
मोल संकल्पना के आधार पर निम्नलिखित रासायनिक अभिक्रियाओं…
Explain the following reactions using the mole concept
(a) C + 1/2 O2 → CO
(b) 1/3 Al_2O3 + 2 HCl → 2/3 AlCl3 + H_2O
(a) C + 1/2 O2 → CO
- 1 mole (12 g) of carbon atoms reacts with 1/2 mole (16 g) of oxygen gas molecules (O2) to form 1 mole (28 g) of carbon monoxide (CO) gas molecules.
(b) 1/3 Al_2O3 + 2 HCl → 2/3 AlCl3 + H_2O
- 1/3 mole of solid aluminium oxide (Al_2O3) reacts completely with 2 moles of hydrochloric acid (HCl) molecules to form 2/3 mole of aluminium chloride (AlCl3) and 1 mole (18 g) of water (H_2O) molecules.