📘 Model Test Questions Class 9 Chemistry Test # 2 for Chapter # 1 (Fundamental of Chemistry)
Prepared by Inam Jazbi – Learn Chemistry
Q1.
Analyze the differences among the following chemical terms by comparing their properties, composition, formation, charge, and examples. Give at least five points for each:
(i) Elements, compounds and mixtures
(ii) Atom, molecule and ion
(iii) Molecule and molecular ion
(iv) cation and anion
(v) Homogenous and Heterogeneous Mixtures
(vi) empirical and molecular formula
(i) Elements, compounds and mixtures
(ii) Atom, molecule and ion
(iii) Molecule and molecular ion
(iv) cation and anion
(v) Homogenous and Heterogeneous Mixtures
(vi) empirical and molecular formula
Q2.
Explain the concept of isotopes and describe the isotopes of the following elements with respect to their symbols, mass numbers, number of fundamental particles and abundance:
Hydrogen
Carbon (C)
Chlorine (Cl)
Uranium (U)
Hydrogen
Carbon (C)
Chlorine (Cl)
Uranium (U)
Q3.
Describe different applications of isotopes.
Q4.
Define element, compound, mixture, atom, molecule, ion, free radical, molecular ion, chemical species, ion, formula unit.
Q5.
Explain why hydrogen and oxygen are considered as element whereas water is compound?
Q6.
What is free radical? How would you explain a free radical in terms of electronic arrangement and chemical behavior?
Q7.
How is an ion different from an atom? Answer with reference to electric charge in electrons. Also explain why fluoride ion is not considered as neon atom?
Q8.
What elements do the following compounds contains?
Washing soda, sugar, sand, caustic soda
Washing soda, sugar, sand, caustic soda
Q9.
Identify mixture, element or compound from the following?
Table salt, ice cream, blood, silicon, coca cola, tin, zinc, water, sulphur
Table salt, ice cream, blood, silicon, coca cola, tin, zinc, water, sulphur
Q10.
Identify the cations, anions, free radicle, molecular ion, molecule from the following.
O² , H⁻ , N₂ , Cl₂ , CO₃²⁻, CO , H₂O , Br⁻ , H₂ , H₃C•, Na+, H•, Cl•, NH₄⁺, H₂⁺
O² , H⁻ , N₂ , Cl₂ , CO₃²⁻, CO , H₂O , Br⁻ , H₂ , H₃C•, Na+, H•, Cl•, NH₄⁺, H₂⁺
Q11.
Justify the classification of molecules.
Q12.
What is valency? Write down names and symbols of any 5 monovalent, divalent and trivalent elements.
Q13.
What is the valency of X in following?
AlX, Fe₂X₃, K₂X, Cr₂X₃
AlX, Fe₂X₃, K₂X, Cr₂X₃
Q14.
What is chemical formula? Describe relationship between empirical and molecular formula? Explain with examples.
Q15.
Write down the chemical, empirical and molecular formula of the following?
Sulphuric acid, Carbon dioxide, Glucose, Benzene, ethene, ethyne, hydrogen peroxide, acetic acid
Sulphuric acid, Carbon dioxide, Glucose, Benzene, ethene, ethyne, hydrogen peroxide, acetic acid
Q16.
Why noble gases do not react with other elements at ordinary conditions?
Q18.
Write chemical formulae of following compounds:
| Compound | Formula | Compound | Formula |
|---|---|---|---|
| Caustic soda | NaOH | Marsh gas | CH₄ |
| Caustic potash | KOH | Bleaching powder | CaOCl₂ |
| Baking soda | NaHCO₃ | Acetylene | C₂H₂ |
| Soda ash | Na₂CO₃ | Oleum | H₂S₂O₇ |
| Washing soda / sodium carbonate | Na₂CO₃.10H₂O | Oil of vitriol | H₂SO₄ |
| Blue vitriol / copper sulphate | CuSO₄.5H₂O | Aqua fortis | HNO₃ |
| Epsom salt / Magnesium sulphate | MgSO₄.7H₂O | Potash alum | K₂SO₄.Al₂(SO₄)₃.24H₂O |
| Gypsum | CaSO₄.2H₂O | Sugar | C₁₂H₂₂O₁₁ |
| Lime stone | CaCO₃ | Pearl ash | K₂CO₃ |
| Carnalite | KCl.MgCl₂.6H₂O | Oxygenated water | H₂O₂ |
| Silica | SiO₂ | Ethylene | C₂H₄ |
📘 MCQs
Prepared by Inam Jazbi – Learn Chemistry.
Click the MCQ to reveal to answer and reason
1. CO₃²⁻ is a/an:
🟥 (a) Molecular ion
🟦 (b) Molecule
🟩 (c) Anion
🟨 (d) Cation
✔ Correct Answer: 🟩 (c) Anion
Reason: CO₃²⁻ carries a negative charge, so it is an anion.
Reason: CO₃²⁻ carries a negative charge, so it is an anion.
2. Boron is a:
🟥 (a) Transition metal
🟦 (b) Non-metal
🟩 (c) Metalloid
🟨 (d) Metal
✔ Correct Answer: 🟩 (c) Metalloid
Reason: Boron shows properties of both metals and non-metals.
Reason: Boron shows properties of both metals and non-metals.
3. At room temperature, this metal exists in liquid state:
🟥 (a) Calcium
🟦 (b) Bromine
🟩 (c) Mercury
🟨 (d) Iron
✔ Correct Answer: 🟩 (c) Mercury
Reason: Mercury is the only metal that is liquid at room temperature.
Reason: Mercury is the only metal that is liquid at room temperature.
4. NH₄⁺ is a/an:
🟥 (a) Molecular ion
🟦 (b) Molecule
🟩 (c) Anion
🟨 (d) Cation
✔ Correct Answer: 🟨 (d) Cation
Reason: NH₄⁺ carries a positive charge, so it is a cation.
Reason: NH₄⁺ carries a positive charge, so it is a cation.
5. The molecular formula of ozone is:
🟥 (a) O₂
🟦 (b) O₃
🟩 (c) P₄
🟨 (d) S₈
✔ Correct Answer: 🟦 (b) O₃
Reason: Ozone is a triatomic form of oxygen.
Reason: Ozone is a triatomic form of oxygen.
6. Which of the following can be separated by physical means?
🟥 (a) Mixture
🟦 (b) Element
🟩 (c) Compound
🟨 (d) Substance
✔ Correct Answer: 🟥 (a) Mixture
Reason: Mixtures can be separated by physical methods.
Reason: Mixtures can be separated by physical methods.
7. The empirical formula of hydrogen peroxide is:
🟥 (a) H₂O₂
🟦 (b) HO
🟩 (c) OH
🟨 (d) O₂H₂
✔ Correct Answer: 🟦 (b) HO
Reason: Empirical formula shows simplest ratio of atoms.
Reason: Empirical formula shows simplest ratio of atoms.
8. A molecule consists of two atoms is:
🟥 (a) Hetero atomic molecule
🟦 (b) Monoatomic molecule
🟩 (c) Polyatomic molecule
🟨 (d) Diatomic molecule
✔ Correct Answer: 🟨 (d) Diatomic molecule
Reason: Diatomic molecules contain two atoms.
Reason: Diatomic molecules contain two atoms.
9. A formula that indicates actual number and type of atoms in a molecule is called:
🟥 (a) Chemical formula
🟦 (b) Empirical formula
🟩 (c) Molecular formula
🟨 (d) Formula mass
✔ Correct Answer: 🟩 (c) Molecular formula
Reason: It shows actual number of atoms in a molecule.
Reason: It shows actual number of atoms in a molecule.
10. Which of the following is a homo atomic molecule?
🟥 (a) H₂
🟦 (b) NH₃
🟩 (c) H₂O
🟨 (d) CO₂
✔ Correct Answer: 🟥 (a) H₂
Reason: Homo atomic molecules contain same type of atoms.
Reason: Homo atomic molecules contain same type of atoms.
11. The radioactive isotope of hydrogen is:
🟥 (a) Deuterium
🟦 (b) Tritium
🟩 (c) Protium
🟨 (d) None of them
✔ Correct Answer: 🟦 (b) Tritium
Reason: Tritium is the only radioactive isotope of hydrogen.
Reason: Tritium is the only radioactive isotope of hydrogen.
12. Owing to same atomic number, isotopes have the same:
🟥 (a) Thermal
🟦 (b) Chemical
🟩 (c) Electrical
🟨 (d) Physical
✔ Correct Answer: 🟦 (b) Chemical
Reason: Chemical properties depend on electron arrangement, same in isotopes.
Reason: Chemical properties depend on electron arrangement, same in isotopes.
13. Cl–35 is found in nature up to:
🟥 (a) 35%
🟦 (b) 75%
🟩 (c) 30%
🟨 (d) 25%
✔ Correct Answer: 🟦 (b) 75%
Reason: Chlorine-35 is the most abundant natural isotope (~75%).
Reason: Chlorine-35 is the most abundant natural isotope (~75%).
14. There are total monoisotopic elements:
🟥 (a) 23
🟦 (b) 21
🟩 (c) 33
🟨 (d) 31
✔ Correct Answer: 🟥 (a) 23
Reason: About 23 elements occur naturally as single-isotope elements.
Reason: About 23 elements occur naturally as single-isotope elements.
15. The chemical formula of caustic soda is:
🟥 (a) KOH
🟦 (b) NaOH
🟩 (c) NaCl
🟨 (d) CaCO₃
✔ Correct Answer: 🟦 (b) NaOH
Reason: Caustic soda is sodium hydroxide.
Reason: Caustic soda is sodium hydroxide.
16. The Latin name of sodium is:
🟥 (a) Aurum
🟦 (b) Ferrum
🟩 (c) Kalium
🟨 (d) Natrium
✔ Correct Answer: 🟨 (d) Natrium
Reason: Sodium derives its symbol Na from Natrium.
Reason: Sodium derives its symbol Na from Natrium.
17. Kalium is the Latin name for:
🟥 (a) Iron
🟦 (b) Potassium
🟩 (c) Sodium
🟨 (d) Fluorine
✔ Correct Answer: 🟦 (b) Potassium
Reason: Potassium symbol K comes from Kalium.
Reason: Potassium symbol K comes from Kalium.
18. Monoisotopic elements have:
🟥 (a) 1 isotope
🟦 (b) 2 isotopes
🟩 (c) 3 isotopes
🟨 (d) No isotopes
✔ Correct Answer: 🟥 (a) 1 isotope
Reason: Monoisotopic elements naturally exist in only one isotope form.
Reason: Monoisotopic elements naturally exist in only one isotope form.
19. The chemical formula of nitric acid is:
🟥 (a) HCl
🟦 (b) HF
🟩 (c) H₂SO₄
🟨 (d) HNO₃
✔ Correct Answer: 🟨 (d) HNO₃
Reason: Nitric acid has formula HNO₃.
Reason: Nitric acid has formula HNO₃.
20. Discovered isotopes:
🟥 (a) Berzelius
🟦 (b) Soddy
🟩 (c) Thomson
🟨 (d) Bohr
✔ Correct Answer: 🟦 (b) Soddy
Reason: Frederick Soddy discovered isotopes.
Reason: Frederick Soddy discovered isotopes.
21. Which isotope is used for sterilization of medical instruments and dressings from harmful bacteria?
🟥 (a) Phosphorus-32
🟦 (b) Strontium-90
🟩 (c) Cobalt-60
🟨 (d) Plutonium-238
✔ Correct Answer: 🟩 (c) Cobalt-60
Reason: Cobalt-60 emits gamma rays used for sterilization.
Reason: Cobalt-60 emits gamma rays used for sterilization.
22. Which isotope is used to stimulate a regular heart beat in heart pacemaker?
🟥 (a) Plutonium-238
🟦 (b) Strontium-90
🟩 (c) Gold-198
🟨 (d) Iodine-131
✔ Correct Answer: 🟥 (a) Plutonium-238
Reason: Plutonium-238 is used as a long-life power source in pacemakers.
Reason: Plutonium-238 is used as a long-life power source in pacemakers.
23. Which isotope is used to estimate the age of fossils?
🟥 (a) Carbon-14
🟦 (b) Strontium-90
🟩 (c) Gold-198
🟨 (d) Iodine-131
✔ Correct Answer: 🟥 (a) Carbon-14
Reason: Carbon dating is used for fossil age determination.
Reason: Carbon dating is used for fossil age determination.
24. Cobalt-60 is used for the treatment of:
🟥 (a) Skin cancer
🟦 (b) Thyroid glands
🟩 (c) Heart beat
🟨 (d) Body cancer
✔ Correct Answer: 🟥 (a) Skin cancer
Reason: Cobalt-60 gamma rays are used in radiotherapy for cancer treatment.
Reason: Cobalt-60 gamma rays are used in radiotherapy for cancer treatment.
25. Which one of the following is NOT a free radical?
🟥 (a) H•
🟦 (b) Cl•
🟩 (c) CH₃•
🟨 (d) CH₄⁺
✔ Correct Answer: 🟨 (d) CH₄⁺
Reason: Free radicals have unpaired electrons; CH₄⁺ is a cation, not a radical.
Reason: Free radicals have unpaired electrons; CH₄⁺ is a cation, not a radical.
26. Free radicals are atoms and groups of atoms having number of:
🟥 (a) Paired electrons
🟦 (b) Unpaired electrons
🟩 (c) Valence electrons
🟨 (d) None of them
✔ Correct Answer: 🟦 (b) Unpaired electrons
Reason: Free radicals contain at least one unpaired electron.
Reason: Free radicals contain at least one unpaired electron.
27. Molecular ion is formed from a molecule by:
🟥 (a) Combination of atoms
🟦 (b) Homolytic breakage
🟩 (c) Ionization
🟨 (d) All of them
✔ Correct Answer: 🟩 (c) Ionization
Reason: Molecular ions form when a molecule gains or loses electrons.
Reason: Molecular ions form when a molecule gains or loses electrons.
28. Which of the following is NOT a reactive species?
🟥 (a) Molecular ion
🟦 (b) Free radical
🟩 (c) Molecule
🟨 (d) None of them
✔ Correct Answer: 🟩 (c) Molecule
Reason: Molecules are generally stable, unlike reactive species.
Reason: Molecules are generally stable, unlike reactive species.
29. The empirical formula of benzene is same as that of:
🟥 (a) Ethene
🟦 (b) Ethyne
🟩 (c) Glucose
🟨 (d) Acetic acid
✔ Correct Answer: 🟥 (b) Ethene
Reason: Benzene (C₆H₆) and ethyne (C₂H₂ simplified → CH) have same empirical ratio.
Reason: Benzene (C₆H₆) and ethyne (C₂H₂ simplified → CH) have same empirical ratio.
30. The empirical formula of glucose is same as that of:
🟥 (a) Ethene
🟦 (b) Ethyne
🟩 (c) Glucose
🟨 (d) Acetic acid
✔ Correct Answer: 🟦 (b) Ethyne
Reason: Both reduce to empirical formula CH (same simplest ratio).
Reason: Both reduce to empirical formula CH (same simplest ratio).
31. Which of the following have same empirical and molecular formulae?
🟥 (a) H₂O
🟦 (b) CH₄
🟩 (c) CO₂
🟨 (d) All of them
✔ Correct Answer: 🟨 (d) All of them
Reason: All are already in simplest whole-number ratio.
Reason: All are already in simplest whole-number ratio.
32. Natrium is the Latin name of this element:
🟥 (a) Nitrogen
🟦 (b) Neon
🟩 (c) Sodium
🟨 (d) Nickel
✔ Correct Answer: 🟩 (c) Sodium
Reason: Sodium comes from Latin Natrium (Na).
Reason: Sodium comes from Latin Natrium (Na).
33. A formula that indicates actual number and type of atoms in a molecule is called:
🟥 (a) Chemical formula
🟦 (b) Empirical formula
🟩 (c) Molecular formula
✔ Correct Answer: 🟩 (c) Molecular formula
Reason: It shows actual number of atoms in a molecule.
Reason: It shows actual number of atoms in a molecule.
34. The empirical formula of hydrogen peroxide is:
🟥 (a) HO
🟦 (b) H₂O₂
🟩 (c) OH
🟨 (d) OH₂
✔ Correct Answer: 🟥 (a) HO
Reason: Simplest ratio of H₂O₂ is HO.
Reason: Simplest ratio of H₂O₂ is HO.
35. Which of the following has an empirical formula of CH₂O?
🟥 (a) C₆H₁₂O₆
🟦 (b) CH₃COOH
🟩 (c) HCHO
🟨 (d) All of them
✔ Correct Answer: 🟥 (d) All of them
Reason: C₆H₁₂O₆ (glucose) → divide by 6 → CH₂O
CH₃COOH (acetic acid) → becomes C₂H₄O₂ → CH₂O
HCHO (formaldehyde) → already CH₂O
✔️ Correct Conclusion
👉 All of them have the same empirical formula: CH₂O
Reason: C₆H₁₂O₆ (glucose) → divide by 6 → CH₂O
CH₃COOH (acetic acid) → becomes C₂H₄O₂ → CH₂O
HCHO (formaldehyde) → already CH₂O
✔️ Correct Conclusion
👉 All of them have the same empirical formula: CH₂O
36. The molecular formula of hydrogen peroxide is:
🟥 (a) H₂O
🟦 (b) H₂O₂
🟩 (c) OH
🟨 (d) HO
✔ Correct Answer: 🟦 (b) H₂O₂
Reason: Hydrogen peroxide exists as H₂O₂ molecule.
Reason: Hydrogen peroxide exists as H₂O₂ molecule.
37. Which of the following is classified as a monoatomic element?
🟥 (a) Oxygen
🟦 (b) Nitrogen
🟩 (c) Milk
🟨 (d) Helium
✔ Correct Answer: 🟨 (d) Helium
Reason: Noble gases exist as single atoms.
Reason: Noble gases exist as single atoms.
38. Which of the following is classified as a diatomic element?
🟥 (a) Oxygen
🟦 (b) Argon
🟩 (c) Neon
🟨 (d) Helium
✔ Correct Answer: 🟥 (a) Oxygen
Reason: Oxygen naturally exists as O₂ molecule.
Reason: Oxygen naturally exists as O₂ molecule.
📘 Smart Answers of Model Test Questions Class 9 Chemistry Test # 2 for Chapter # 1 (Fundamentals of Chemistry)
Prepared by Inam Jazbi – Learn Chemistry
Q1. Analyze the differences among the following chemical terms by comparing their properties, composition, formation, charge, and examples. Give at least five points for each:
(i) Elements, Compounds and Mixtures
(ii) Atom, Molecule and Ion
(iii) Molecule and Molecular ion
(iv) Cation and Anion
(v) Ion and Free Radical
(vi) Homogenous and Heterogeneous Mixtures
(vii) Empirical and Molecular formula
Answer
(i) Elements, Compounds and Mixtures
(ii) Atom, Molecule and Ion
(iii) Molecule and Molecular ion
(iv) Cation and Anion
(v) Ion and Free Radical
(vi) Homogenous and Heterogeneous Mixtures
(vii) Empirical and Molecular formula
Answer
Difference between Elements, Compounds and mixture
| Elements | Compounds | Mixtures |
|---|---|---|
| Made of one kind of atom. | Made of two or more elements chemically combined. | Made of two or more substances physically mixed. |
| Cannot be broken into simpler substances. | Can be decomposed chemically. | Components can be separated physically. |
| Have fixed composition. | Have fixed ratio of elements. | Have no fixed composition. |
| Represented by symbols. | Represented by chemical formulae. | Have no chemical formula. |
| Properties remain same throughout. | Properties differ from constituents. | Constituents retain their properties. |
| Always homogeneous. | Always homogeneous. | May be homogeneous or heterogeneous. |
| Have sharp melting and boiling points. | Have sharp melting and boiling points. | Do not have fixed melting and boiling points. |
| Smallest particle is atom. | Smallest particle is molecule/ion. | Contains atoms, molecules or ions together. |
| Naturally occurring pure substances. | Formed by chemical reactions. | Formed by simple mixing. |
| Example: Iron, Oxygen, Sulphur | Example: H₂O, NaCl, CO₂ | Example: Air, Milk, Brass |
Difference between Atom, Molecule and Ion
| Atom | Molecule | Ion |
|---|---|---|
| Smallest particle of an element. | Smallest particle of an element or compound having independent existence. | Charged particle formed by loss or gain of electrons. |
| May or may not exist independently. | Exists independently. | Usually exists with oppositely charged ions. |
| Electrically neutral. | Electrically neutral. | Has positive or negative charge. |
| Usually unstable and reactive. | Usually stable. | Usually stable but reactive. |
| Represented by symbols. | Represented by molecular formula. | Denoted by symbols with charge. |
| Made of single atom. | Made of two or more atoms chemically combined. | Can be single atom or group of atoms with charge. |
| Mostly has incomplete octet. | Usually has complete octet/duplet. | Usually has complete octet/duplet. |
| Example: Na, H, Fe | Example: H₂O, CO₂, HCl | Example: Na⁺, Cl⁻, SO₄²⁻ |
Difference between Molecule and Molecular Ion
| S.# | Molecule | Molecular Ion |
|---|---|---|
| 1 | Electrically neutral particle. | Charged particle. |
| 2 | Formed by sharing of electrons only. | Formed by gain or loss of electrons by a molecule. |
| 3 | Formed by the combination of atoms. | Formed by the ionization of a molecule. |
| 4 | Molecule is a stable unit. | Molecular ion is a reactive species. |
| 5 | Can exist independently. | Usually exists with oppositely charged ions. |
| 6 | Has no overall charge. | Has positive or negative charge. |
| 7 | Example: H₂O, CO₂ | Example: H₂⁺, O₂⁺, CH₄⁺ |
Difference between Cation and Anion
| S.# | Cation | Anion |
|---|---|---|
| 1 | Positively charged ion. | Negatively charged ion. |
| 2 | Formed by loss of electrons. | Formed by gain of electrons. |
| 3 | Number of protons > electrons. | Number of electrons > protons. |
| 4 | Attracted towards cathode (negative electrode). | Attracted towards anode (positive electrode). |
| 5 | Usually metals form cations. | Usually non-metals form anions. |
| 6 | Smaller in size than neutral atom. | Larger in size than neutral atom. |
| 7 | Examples: Na⁺, Ca²⁺, Al³⁺ | Examples: Cl⁻, O²⁻, SO₄²⁻ |
Difference between Ion and Free Radical
| S.# | Ion | Free Radical |
|---|---|---|
| 1 | It is an atom or group of atoms having charge. | It is an atom or group of atoms with unpaired electron. |
| 2 | It may have positive or negative charge. | It is usually electrically neutral. |
| 3 | Ions exist in crystals and solutions. | Free radicals exist in air and solutions. |
| 4 | Formed by loss or gain of electrons. | Formed by homolytic bond breaking. |
| 5 | Generally more stable. | Usually highly reactive and unstable. |
| 6 | Represented by charge signs (+, −). | Represented by a dot (•). |
| 7 | Exists in ionic compounds or solutions. | Exists temporarily during chemical reactions. |
| 8 | Ions are not affected by the presence of light. | Free radicals are affected by the presence of light. |
| 9 | Example: Na⁺, Cl⁻, SO₄²⁻ | Example: Cl•, OH•, CH₃• |
Difference between Homogeneous and Heterogeneous Mixtures
| S.# | Homogeneous Mixture | Heterogeneous Mixture |
|---|---|---|
| 1 | Uniform composition throughout the mixture. | Non-uniform composition. |
| 2 | Components are not visibly separate. | Components are visibly separate. |
| 3 | Single phase present. | Two or more phases present. |
| 4 | Same properties in every part. | Different properties in different parts. |
| 5 | Separation is difficult (needs special methods). | Separation is easy (simple physical methods). |
| 6 | Particles are very small. | Particles are larger and often visible. |
| 7 | All solutions are homogeneous mixtures. | All suspensions are heterogeneous mixtures. |
| 8 | Examples: air, rainwater, vinegar, salt solution, brass | Examples: seawater, pizza, mixture of sodium chloride and sand |
Difference between Empirical Formula and Molecular Formula
| S.# | Empirical Formula | Molecular Formula |
|---|---|---|
| 1 | Shows simplest whole number ratio of atoms. | Shows actual number of atoms in a molecule. |
| 2 | Does not give real structure or exact count. | Gives exact composition of a molecule. |
| 3 | May or may not be same as molecular formula. | Always a multiple of empirical formula. |
| 4 | May not represent real molecule (shows ratio only). | Represents real molecule. |
| 5 | Usually simpler form. | Usually larger or same as empirical formula. |
| 6 | Derived from percentage composition. | Derived from empirical formula using molar mass. |
| 7 | Used for ionic and covalent compounds. | Used only for covalent (molecular) compounds. |
| 8 | Can be same for different compounds. | May differ for compounds with same empirical formula. |
| 9 | Always simplest form. | Can be multiple of empirical formula (M.F = E.F × n). |
| 10 | Can be derived by dividing subscripts by common factor. | Found using empirical formula and molar mass. |
| 11 | Example: CH₂O (glucose), NaCl | Example: C₆H₁₂O₆ (glucose), C₆H₆ (benzene) |
Q2. Explain the concept of isotopes and describe the isotopes of the following elements with respect to their symbols, mass numbers, number of fundamental particles and abundance:
Hydrogen
Carbon (C)
Chlorine (Cl)
Uranium (U)
Answer
Isotopes are atoms of the same element that have the same atomic number (same protons and electrons) but different mass numbers or atomic masses due to different neutrons.
They show similar chemical properties because their electronic configuration is the same, but different physical properties because their atomic masses differ.
✦ Protium: ➡️ Symbol = ¹₁H, ➡️ Atomic No. = 1, ➡️ Mass No. = 1, ➡️ No. of Protons = 1, ➡️ No. of Electrons = 1, ➡️ No. of Neutrons = 0, ➡️ % Abundance = 99.985%
✦ Deuterium: ➡️ Symbol = ²₁H, ➡️ Atomic No. = 1, ➡️ Mass No. = 2, ➡️ No. of Protons = 1, ➡️ No. of Electrons = 1, ➡️ No. of Neutrons = 1, ➡️ % Abundance = 0.0156%
✦ Tritium: ➡️ Symbol = ³₁H, ➡️ Atomic No. = 1, ➡️ Mass No. = 3, ➡️ No. of Protons = 1, ➡️ No. of Electrons = 1, ➡️ No. of Neutrons = 2, ➡️ % Abundance = 4 × 10⁻¹⁵%
✦ Carbon-12 (¹²₆C): ➡️ Z = 6, ➡️ A = 12, ➡️ Protons = 6, ➡️ Electrons = 6, ➡️ Neutrons = 6, ➡️ % Abundance = 98.889%
✦ Carbon-13 (¹³₆C): ➡️ Z = 6, ➡️ A = 13, ➡️ Protons = 6, ➡️ Electrons = 6, ➡️ Neutrons = 7, ➡️ % Abundance = 1.111%
✦ Carbon-14 (¹⁴₆C): ➡️ Z = 6, ➡️ A = 14, ➡️ Protons = 6, ➡️ Electrons = 6, ➡️ Neutrons = 8, ➡️ % Abundance = trace (radioactive)
✦ Chlorine-35 (³⁵₁₇Cl): ➡️ Z = 17, ➡️ A = 35, ➡️ Protons = 17, ➡️ Electrons = 17, ➡️ Neutrons = 18, ➡️ % Abundance = 75.53%
✦ Chlorine-37 (³⁷₁₇Cl): ➡️ Z = 17, ➡️ A = 37, ➡️ Protons = 17, ➡️ Electrons = 17, ➡️ Neutrons = 20, ➡️ % Abundance = 24.47%
✦ Uranium-234 (²³⁴₉₂U): ➡️ Z = 92, ➡️ A = 234, ➡️ Protons = 92, ➡️ Electrons = 92, ➡️ Neutrons = 142, ➡️ % Abundance = 0.0055%
✦ Uranium-235 (²³⁵₉₂U): ➡️ Z = 92, ➡️ A = 235, ➡️ Protons = 92, ➡️ Electrons = 92, ➡️ Neutrons = 143, ➡️ % Abundance = 0.7200%
✦ Uranium-238 (²³⁸₉₂U): ➡️ Z = 92, ➡️ A = 238, ➡️ Protons = 92, ➡️ Electrons = 92, ➡️ Neutrons = 146, ➡️ % Abundance = 99.2745%
Isotopes of Hydrogen
There are three isotopes of hydrogen namely protium or ordinary hydrogen, deuterium or heavy hydrogen, tritium or radioactive hydrogen.
✦ Protium: ➡️ Symbol = ¹₁H, ➡️ Atomic No. = 1, ➡️ Mass No. = 1, ➡️ No. of Protons = 1, ➡️ No. of Electrons = 1, ➡️ No. of Neutrons = 0, ➡️ % Abundance = 99.985%
✦ Deuterium: ➡️ Symbol = ²₁H, ➡️ Atomic No. = 1, ➡️ Mass No. = 2, ➡️ No. of Protons = 1, ➡️ No. of Electrons = 1, ➡️ No. of Neutrons = 1, ➡️ % Abundance = 0.0156%
✦ Tritium: ➡️ Symbol = ³₁H, ➡️ Atomic No. = 1, ➡️ Mass No. = 3, ➡️ No. of Protons = 1, ➡️ No. of Electrons = 1, ➡️ No. of Neutrons = 2, ➡️ % Abundance = 4 × 10⁻¹⁵%
| Property | Symbol | Atomic No. | Mass No. | Protons | Electrons | Neutrons | % Abundance |
|---|---|---|---|---|---|---|---|
| Protium | ¹₁H | 1 | 1 | 1 | 1 | 0 | 99.985% |
| Deuterium | ²₁H | 1 | 2 | 1 | 1 | 1 | 0.0156% |
| Tritium | ³₁H | 1 | 3 | 1 | 1 | 2 | 4 × 10⁻¹⁵% |
Isotopes of Carbon
There are two stable isotopes and one radioactive isotope of carbon. Carbon-12 contains 6 protons and 6 neutrons, Carbon-13 possesses 6 protons and 7 neutrons, and Carbon-14 contains 6 protons and 8 neutrons. Carbon-12 is the most abundant (98.89%) isotope.
✦ Carbon-12 (¹²₆C): ➡️ Z = 6, ➡️ A = 12, ➡️ Protons = 6, ➡️ Electrons = 6, ➡️ Neutrons = 6, ➡️ % Abundance = 98.889%
✦ Carbon-13 (¹³₆C): ➡️ Z = 6, ➡️ A = 13, ➡️ Protons = 6, ➡️ Electrons = 6, ➡️ Neutrons = 7, ➡️ % Abundance = 1.111%
✦ Carbon-14 (¹⁴₆C): ➡️ Z = 6, ➡️ A = 14, ➡️ Protons = 6, ➡️ Electrons = 6, ➡️ Neutrons = 8, ➡️ % Abundance = trace (radioactive)
| Property | Symbol | Atomic No. | Mass No. | Protons | Electrons | Neutrons | % Abundance |
|---|---|---|---|---|---|---|---|
| Carbon-12 | ¹²₆C | 6 | 12 | 6 | 6 | 6 | 98.889% |
| Carbon-13 | ¹³₆C | 6 | 13 | 6 | 6 | 7 | 1.111% |
| Carbon-14 | ¹⁴₆C | 6 | 14 | 6 | 6 | 8 | trace (radioactive) |
Isotopes of Oxygen
| Property | Symbol | Atomic No. | Mass No. | Protons | Electrons | Neutrons | % Abundance |
|---|---|---|---|---|---|---|---|
| Oxygen-16 | ¹⁶₈O | 8 | 16 | 8 | 8 | 8 | 99.757% |
| Oxygen-17 | ¹⁷₈O | 8 | 17 | 8 | 8 | 9 | 0.038% |
| Oxygen-18 | ¹⁸₈O | 8 | 18 | 8 | 8 | 10 | 0.205% |
Isotopes of Chlorine
There are two isotopes of chlorine with atomic number 17 and mass number 35 and 37. Chlorine-35 is about 75% and chlorine-37 is about 25% abundant in nature.
✦ Chlorine-35 (³⁵₁₇Cl): ➡️ Z = 17, ➡️ A = 35, ➡️ Protons = 17, ➡️ Electrons = 17, ➡️ Neutrons = 18, ➡️ % Abundance = 75.53%
✦ Chlorine-37 (³⁷₁₇Cl): ➡️ Z = 17, ➡️ A = 37, ➡️ Protons = 17, ➡️ Electrons = 17, ➡️ Neutrons = 20, ➡️ % Abundance = 24.47%
| Property | Symbol | Atomic No. | Mass No. | Protons | Electrons | Neutrons | % Abundance |
|---|---|---|---|---|---|---|---|
| Chlorine-35 | ³⁵₁₇Cl | 17 | 35 | 17 | 17 | 18 | 75.53% |
| Chlorine-37 | ³⁷₁₇Cl | 17 | 37 | 17 | 17 | 20 | 24.47% |
Isotopes of Uranium
There are three common isotopes of uranium with atomic number 92 and mass number 234, 235 and 238 respectively. Uranium is found mostly as Uranium-238 in nature.
✦ Uranium-234 (²³⁴₉₂U): ➡️ Z = 92, ➡️ A = 234, ➡️ Protons = 92, ➡️ Electrons = 92, ➡️ Neutrons = 142, ➡️ % Abundance = 0.0055%
✦ Uranium-235 (²³⁵₉₂U): ➡️ Z = 92, ➡️ A = 235, ➡️ Protons = 92, ➡️ Electrons = 92, ➡️ Neutrons = 143, ➡️ % Abundance = 0.7200%
✦ Uranium-238 (²³⁸₉₂U): ➡️ Z = 92, ➡️ A = 238, ➡️ Protons = 92, ➡️ Electrons = 92, ➡️ Neutrons = 146, ➡️ % Abundance = 99.2745%
| Property | Symbol | Atomic No. | Mass No. | Protons | Electrons | Neutrons | % Abundance |
|---|---|---|---|---|---|---|---|
| Uranium-234 | ²³⁴₉₂U | 92 | 234 | 92 | 92 | 142 | 0.0055% |
| Uranium-235 | ²³⁵₉₂U | 92 | 235 | 92 | 92 | 143 | 0.7200% |
| Uranium-238 | ²³⁸₉₂U | 92 | 238 | 92 | 92 | 146 | 99.2745% |
Q3. Describe different applications of isotopes.
📝 Answer
➡️ Phosphorus-32: Radiotherapy – Treatment of skin cancer
➡️ Strontium-90: Radiotherapy – Treatment of skin cancer
➡️ Cobalt-60: Radiotherapy – Treatment of internal cancers (penetrating power)
➡️ Iodine-131: Radiotherapy – Detection of thyroid glands
➡️ Technetium: Radiotherapy – Monitor bone growth during fracture healing
➡️ Gamma rays of Cobalt-60: Medical instrumentation – Sterilization of instruments and dressings
➡️ Americium-241: Safety & industries – Smoke detectors, backscatter gauges, coal ash measurement
➡️ Gold-198 & Technetium-99: Environmental tracing – Track sewage, water pollution, and sand movement
➡️ Uranium-235: Power generation – Electricity production via steam turbines
➡️ Plutonium-238: Medicine – Heart pacemakers (stimulates regular heartbeat)
➡️ Carbon-14: Archaeology & geology – Dating (age) fossils
➡️ Strontium-90: Radiotherapy – Treatment of skin cancer
➡️ Cobalt-60: Radiotherapy – Treatment of internal cancers (penetrating power)
➡️ Iodine-131: Radiotherapy – Detection of thyroid glands
➡️ Technetium: Radiotherapy – Monitor bone growth during fracture healing
➡️ Gamma rays of Cobalt-60: Medical instrumentation – Sterilization of instruments and dressings
➡️ Americium-241: Safety & industries – Smoke detectors, backscatter gauges, coal ash measurement
➡️ Gold-198 & Technetium-99: Environmental tracing – Track sewage, water pollution, and sand movement
➡️ Uranium-235: Power generation – Electricity production via steam turbines
➡️ Plutonium-238: Medicine – Heart pacemakers (stimulates regular heartbeat)
➡️ Carbon-14: Archaeology & geology – Dating (age) fossils
Q4. Define element, compound, mixture, atom, molecule, ion, free radical, molecular ion, chemical species, ion, formula unit.
📝 Answer
Element
An element is a pure substance made up of only one type of atoms having the same atomic number. It cannot be broken into simpler substances by chemical reactions.
Compound
A compound is a pure substance formed when two or more elements are chemically combined in a fixed ratio. It can only be separated by chemical methods. It has its own properties different from its elements.
Mixture
A mixture is a combination of two or more substances (elements or compounds) physically mixed in any ratio. Its components can be separated by physical methods like filtration, evaporation, or distillation.
Example: air, salt water.
Atom
An atom is the smallest neutral particle of an element that can take part in chemical reactions. It is the basic building block of matter.
Molecule
A molecule is the smallest particle of a substance that can exist independently and shows all chemical properties of that substance. It is made of two or more atoms chemically bonded together.
Ion
An ion is an atom or group of atoms that carries a positive or negative charge due to loss or gain of electrons.
Examples: Na⁺, NH₄⁺, Cl⁻, SO₄²⁻.
Free Radical
A free radical is an atom or group of atoms that contains one or more unpaired electrons. It is highly reactive and unstable e.g. Cl•, OH•, CH₃•
Molecular Ion
A molecular ion is a molecule that carries an electric charge due to loss or gain of electrons, but still retains its molecular structure.
Example: CH₄⁺, CO⁺
An element is a pure substance made up of only one type of atoms having the same atomic number. It cannot be broken into simpler substances by chemical reactions.
Compound
A compound is a pure substance formed when two or more elements are chemically combined in a fixed ratio. It can only be separated by chemical methods. It has its own properties different from its elements.
Mixture
A mixture is a combination of two or more substances (elements or compounds) physically mixed in any ratio. Its components can be separated by physical methods like filtration, evaporation, or distillation.
Example: air, salt water.
Atom
An atom is the smallest neutral particle of an element that can take part in chemical reactions. It is the basic building block of matter.
Molecule
A molecule is the smallest particle of a substance that can exist independently and shows all chemical properties of that substance. It is made of two or more atoms chemically bonded together.
Ion
An ion is an atom or group of atoms that carries a positive or negative charge due to loss or gain of electrons.
Examples: Na⁺, NH₄⁺, Cl⁻, SO₄²⁻.
Free Radical
A free radical is an atom or group of atoms that contains one or more unpaired electrons. It is highly reactive and unstable e.g. Cl•, OH•, CH₃•
Molecular Ion
A molecular ion is a molecule that carries an electric charge due to loss or gain of electrons, but still retains its molecular structure.
Example: CH₄⁺, CO⁺
Q5. Explain why hydrogen and oxygen are considered as element whereas water is compound?
📝 Answer
Hydrogen and oxygen are elements because each is made of only one type of atom and cannot be broken down into simpler substances by ordinary chemical methods.
Water is a compound because it contains two different elements, hydrogen and oxygen, chemically combined in a fixed ratio, and it can be separated into its elements by chemical processes such as electrolysis.
Water is a compound because it contains two different elements, hydrogen and oxygen, chemically combined in a fixed ratio, and it can be separated into its elements by chemical processes such as electrolysis.
Q6. What is free radical? How would you explain a free radical in terms of electronic arrangement and chemical behavior?
📝 Answer
Definition of free radical
A free radical is an atom or group of atoms that has one or more unpaired electrons in its outer shell. e.g. Cl•, OH•, CH₃•
Electronic arrangement:
It contains an odd electron, so it does not have a complete valence shell.
Chemical behavior:
Because of the unpaired electron, it is highly reactive and quickly tries to pair its electron by reacting with other substances, often starting chain reactions.
A free radical is an atom or group of atoms that has one or more unpaired electrons in its outer shell. e.g. Cl•, OH•, CH₃•
Electronic arrangement:
It contains an odd electron, so it does not have a complete valence shell.
Chemical behavior:
Because of the unpaired electron, it is highly reactive and quickly tries to pair its electron by reacting with other substances, often starting chain reactions.
Chemistry Notes
Q7. How is an ion different from an atom? Answer with reference to electric charge in electrons. Also explain why fluoride ion is not considered as neon atom?
📝 Answer
Ion vs Atom (electronic charge):
An atom is electrically neutral because it has equal number of protons and electrons.
Example: Sodium atom (Na), Chlorine atom (Cl)
An ion carries charge due to loss or gain of electrons.
Examples:
Na⁺ (sodium ion) → formed when sodium loses 1 electron
Cl⁻ (chloride ion) → formed when chlorine gains 1 electron
Mg²⁺ (magnesium ion) → formed when magnesium loses 2 electrons
O²⁻ (oxide ion) → formed when oxygen gains 2 electrons
Fluoride ion vs Neon atom:
✦ Fluoride ion (F⁻) has atomic number 9, so it has 9 protons.
✦ It gains 1 electron, so it has 10 electrons, giving it a −1 charge.
✦ Neon atom has atomic number 10, so it has 10 protons and 10 electrons.
✦ Therefore, F⁻ and Ne are different because their atomic numbers (protons) are different, even though both have 10 electrons.
An atom is electrically neutral because it has equal number of protons and electrons.
Example: Sodium atom (Na), Chlorine atom (Cl)
An ion carries charge due to loss or gain of electrons.
Examples:
Na⁺ (sodium ion) → formed when sodium loses 1 electron
Cl⁻ (chloride ion) → formed when chlorine gains 1 electron
Mg²⁺ (magnesium ion) → formed when magnesium loses 2 electrons
O²⁻ (oxide ion) → formed when oxygen gains 2 electrons
Fluoride ion vs Neon atom:
✦ Fluoride ion (F⁻) has atomic number 9, so it has 9 protons.
✦ It gains 1 electron, so it has 10 electrons, giving it a −1 charge.
✦ Neon atom has atomic number 10, so it has 10 protons and 10 electrons.
✦ Therefore, F⁻ and Ne are different because their atomic numbers (protons) are different, even though both have 10 electrons.
Q8. What elements do the following compounds contain?
Washing soda, sugar, sand, caustic soda
📝 Answer
Washing soda (Na2CO3.10H2O):
Sodium, carbon, oxygen and hydrogen (4 elements, 36 atoms)
Sugar/Sucrose (C12H12O11): Carbon, hydrogen and oxygen (3 elements, 35 atoms)
Sand/Silica (SiO2): Silicon and oxygen (2 elements, 3 atoms)
Caustic soda (NaOH): Sodium, oxygen and hydrogen (3 elements, 3 atoms)
Sugar/Sucrose (C12H12O11): Carbon, hydrogen and oxygen (3 elements, 35 atoms)
Sand/Silica (SiO2): Silicon and oxygen (2 elements, 3 atoms)
Caustic soda (NaOH): Sodium, oxygen and hydrogen (3 elements, 3 atoms)
Q9. Identify mixture, element or compound from the following?
Table salt, ice cream, blood, silicon, coca cola, tin, zinc, water, sulphur
📝 Answer
Elements:
Silicon, Tin, Zinc, Sulphur
Compound: Table salt, Water
Mixture: Ice cream, Blood, Coca cola
Compound: Table salt, Water
Mixture: Ice cream, Blood, Coca cola
Chemistry Notes
Q10. Identify the cations, anions, free radicle, molecular ion, molecule from the following.
O²⁻ , H⁻ , N₂ , Cl₂ , CO₃²⁻, CO , H₂O , Br⁻ , H₂ , H₃C•, Na⁺, H•, Cl•, NH₄⁺, H₂⁺
O²⁻ , H⁻ , N₂ , Cl₂ , CO₃²⁻, CO , H₂O , Br⁻ , H₂ , H₃C•, Na⁺, H•, Cl•, NH₄⁺, H₂⁺
📝 Answer
Cations:
Na⁺, NH₄⁺
Anions: O²⁻, H⁻, CO₃²⁻, Br⁻
Free radical: H₃C•, H•, Cl•
Molecular ion: H₂⁺
Molecule: N₂, Cl₂, CO, H₂O, H₂
Anions: O²⁻, H⁻, CO₃²⁻, Br⁻
Free radical: H₃C•, H•, Cl•
Molecular ion: H₂⁺
Molecule: N₂, Cl₂, CO, H₂O, H₂
Chemistry Notes
Q11. Justify the classification of molecules.
📝 Answer
Types or Classification of Molecules
1. Heteroatomic Molecules: Made of different atoms.
Examples: CO, NO, H₂O, CO₂, NH₃, CH₄
2. Homoatomic Molecules: Made of same atoms.
Examples: H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂, O₃, P₄, S₈
Subtypes:
i) Monoatomic: 1 atom
Examples: He, Ne, Ar, Kr, Xe, Rn
ii) Diatomic: 2 atoms
Examples: H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂, CO, NO
iii) Triatomic: 3 atoms
Examples: O₃, H₂O, CO₂
iv) Polyatomic: Many atoms
Examples: P₄, S₄, S₆, S₈, H₂SO₄, C₆H₁₂O₆
1. Heteroatomic Molecules: Made of different atoms.
Examples: CO, NO, H₂O, CO₂, NH₃, CH₄
2. Homoatomic Molecules: Made of same atoms.
Examples: H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂, O₃, P₄, S₈
Subtypes:
i) Monoatomic: 1 atom
Examples: He, Ne, Ar, Kr, Xe, Rn
ii) Diatomic: 2 atoms
Examples: H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂, CO, NO
iii) Triatomic: 3 atoms
Examples: O₃, H₂O, CO₂
iv) Polyatomic: Many atoms
Examples: P₄, S₄, S₆, S₈, H₂SO₄, C₆H₁₂O₆
Chemistry Notes
Q12. What is valency? Write down names and symbols of any 5 monovalent, divalent and trivalent elements.
📝 Answer
Old Definition:
Valency is the combining or displacing capacity of an element with other elements.
Modern Definition:
Valency is the number of electrons an atom loses, gains, or shares to complete its outer shell (octet).
Types of Elements on the Basis of Valency
1. Monovalent Elements: Examples: Li, Na, K, Rb, Cs, Cu, Au, Ag, F, Cl, Br, I, H etc.
2. Divalent Elements: Examples: Be, Mg, Ca, Ba, Sr, Zn, Cd, Fe, Co, Ni, Sn, Pb, Mn, O, S, Se, Te, Cu etc.
3. Trivalent Elements: Examples: B, Al, Cr, Bi, Sb, As, Fe, Mn, Sc, Au, N, P etc.
Valency is the combining or displacing capacity of an element with other elements.
Modern Definition:
Valency is the number of electrons an atom loses, gains, or shares to complete its outer shell (octet).
Types of Elements on the Basis of Valency
1. Monovalent Elements: Examples: Li, Na, K, Rb, Cs, Cu, Au, Ag, F, Cl, Br, I, H etc.
2. Divalent Elements: Examples: Be, Mg, Ca, Ba, Sr, Zn, Cd, Fe, Co, Ni, Sn, Pb, Mn, O, S, Se, Te, Cu etc.
3. Trivalent Elements: Examples: B, Al, Cr, Bi, Sb, As, Fe, Mn, Sc, Au, N, P etc.
Chemistry Notes
Q13. What is the valency of X in following? AlX, Fe₂X₃, K₂X, Cr₂X₃
📝 Answer
Determination of Valency of X in Compound
✦ AlX → Valency of X = 3 (Reason: Al has valency 3, so X must be 3 to balance charge).
✦ Fe₂X₃ → Valency of X = 2 (Reason: 2 Fe = 2×3 = 6 total, so 3 X must also total 6 → X = 2).
✦ K₂X → Valency of X = 1 (Reason: 2 K = 2×1 = 2 total, so X must be 1).
✦ Cr₂X₃ → Valency of X = 2 (Reason: 2 Cr = 2×3 = 6 total, so 3 X must be 6 → X = 2).
✦ AlX → Valency of X = 3 (Reason: Al has valency 3, so X must be 3 to balance charge).
✦ Fe₂X₃ → Valency of X = 2 (Reason: 2 Fe = 2×3 = 6 total, so 3 X must also total 6 → X = 2).
✦ K₂X → Valency of X = 1 (Reason: 2 K = 2×1 = 2 total, so X must be 1).
✦ Cr₂X₃ → Valency of X = 2 (Reason: 2 Cr = 2×3 = 6 total, so 3 X must be 6 → X = 2).
Chemistry Notes
Q14. What is chemical formula? Describe relationship between empirical and molecular formula? Explain with examples.
📝 Answer
Definition:
“Chemical formula is an abbreviation used for the full name of a compound by the help of symbols”. E.g. Chemical formula of water is H₂O showing that 2 atoms of hydrogen combine with 1 atom of oxygen.
Relationship:
The molecular formula of a substance is an integral multiple of the empirical formula i.e.
Molecular Formula = (Empirical Formula)ₙ
Note:
Usually ionic compounds (NaCl, MgCl₂, MgO etc.) have same molecular and empirical formula.
“Chemical formula is an abbreviation used for the full name of a compound by the help of symbols”. E.g. Chemical formula of water is H₂O showing that 2 atoms of hydrogen combine with 1 atom of oxygen.
Relationship:
The molecular formula of a substance is an integral multiple of the empirical formula i.e.
Molecular Formula = (Empirical Formula)ₙ
Note:
Usually ionic compounds (NaCl, MgCl₂, MgO etc.) have same molecular and empirical formula.
Chemistry Notes
Q15. Write down the chemical, empirical and molecular formula of the following?
Sulphuric acid, Carbon dioxide, Glucose, Benzene, ethene, ethyne, hydrogen peroxide, acetic acid
Sulphuric acid, Carbon dioxide, Glucose, Benzene, ethene, ethyne, hydrogen peroxide, acetic acid
📝 Answer
✦ Sulphuric acid ➡️ Empirical formula: H₂SO₄ ➡️ Molecular formula: H₂SO₄
✦ Carbon dioxide ➡️ Empirical formula: CO₂ ➡️ Molecular formula: CO₂
✦ Glucose ➡️ Empirical formula: CH₂O ➡️ Molecular formula: C₆H₁₂O₆
✦ Benzene ➡️ Empirical formula: CH ➡️ Molecular formula: C₆H₆
✦ Ethene ➡️ Empirical formula: CH₂ ➡️ Molecular formula: C₂H₄
✦ Ethyne ➡️ Empirical formula: CH ➡️ Molecular formula: C₂H₂
✦ Hydrogen peroxide ➡️ Empirical formula: HO ➡️ Molecular formula: H₂O₂
✦ Acetic acid ➡️ Empirical formula: CH₂O ➡️ Molecular formula: CH₃COOH
✦ Carbon dioxide ➡️ Empirical formula: CO₂ ➡️ Molecular formula: CO₂
✦ Glucose ➡️ Empirical formula: CH₂O ➡️ Molecular formula: C₆H₁₂O₆
✦ Benzene ➡️ Empirical formula: CH ➡️ Molecular formula: C₆H₆
✦ Ethene ➡️ Empirical formula: CH₂ ➡️ Molecular formula: C₂H₄
✦ Ethyne ➡️ Empirical formula: CH ➡️ Molecular formula: C₂H₂
✦ Hydrogen peroxide ➡️ Empirical formula: HO ➡️ Molecular formula: H₂O₂
✦ Acetic acid ➡️ Empirical formula: CH₂O ➡️ Molecular formula: CH₃COOH
Chemistry Notes
Q16. Why noble gases do not react with other elements at ordinary conditions?
📝 Answer
Reason:
Noble gases do not react under ordinary conditions because they already have a completely filled outermost electron shell, making them very stable.
Since their valence shell is full, they have no tendency to gain, lose, or share electrons, so they remain chemically inert.
Noble gases do not react under ordinary conditions because they already have a completely filled outermost electron shell, making them very stable.
Since their valence shell is full, they have no tendency to gain, lose, or share electrons, so they remain chemically inert.
Q17. Write chemical formulae of following compounds:
📝 Answer
| Compound | Chemical Formula | Compound | Chemical Formula |
|---|---|---|---|
| Caustic soda | NaOH | Marsh gas | CH₄ |
| Caustic potash | KOH | Bleaching powder | CaOCl₂ |
| Baking soda | NaHCO₃ | Acetylene | C₂H₂ |
| Soda ash | Na₂CO₃ | Oleum | H₂S₂O₇ |
| Washing soda | Na₂CO₃.10H₂O | Oil of vitriol | H₂SO₄ |
| Blue vitriol | CuSO₄.5H₂O | Aqua fortis | HNO₃ |
| Epsom salt | MgSO₄.7H₂O | Potash alum | K₂SO₄.Al₂(SO₄)₃.24H₂O |
| Gypsum | CaSO₄.2H₂O | Sugar | C₁₂H₂₂O₁₁ |
| Limestone | CaCO₃ | Pearl ash | K₂CO₃ |
| Carnalite | KCl.MgCl₂.6H₂O | Oxygenated water | H₂O₂ |
| Silica | SiO₂ | Ethylene | C₂H₄ |
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