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Q1. What happens to iron articles when left exposed for some time?
They get coated with a reddish-brown powder.Iron reacts with oxygen and moisture in the air to form hydrated iron(III) oxide (Fe₂O₃·xH₂O), which appears as a reddish-brown flaky substance commonly called rust.
Q2. What is the common name for the process where iron gets coated with a reddish-brown powder?
RustingRusting is the specific term for corrosion of iron and its alloys, forming a reddish-brown iron oxide layer that weakens the metal structure.
Q3. What is the general term for the process where a metal is attacked by moisture, acids, etc.?
CorrosionCorrosion is the gradual destruction of materials (usually metals) by chemical reactions with their environment, including moisture, oxygen, acids, and salts.
Q4. What color coating is formed on copper due to corrosion?
GreenCopper reacts with moist air to form a green coating of basic copper carbonate (Cu₂(OH)₂CO₃), seen on old copper roofs and statues like the Statue of Liberty.
Q5. What color coating is formed on silver due to corrosion?
BlackSilver reacts with hydrogen sulphide (H₂S) present in air to form a black coating of silver sulphide (Ag₂S), which is why old silver jewelry and utensils appear tarnished.
Q6. Which of the following objects is specifically mentioned as being damaged by corrosion?
Car bodies and bridgesCorrosion affects iron and steel structures significantly; car bodies develop rust spots, and bridges can suffer structural weakness, requiring costly maintenance and replacement.
Q7. What is a serious economic problem mentioned regarding corrosion?
An enormous amount of money is spent to replace damaged iron.Corrosion causes billions of dollars in economic losses annually due to replacement of rusted infrastructure, vehicles, machinery, and industrial equipment.
Q8. What happens to fats and oils when they are oxidised?
They become rancid.Oxidation of unsaturated fats and oils produces volatile aldehydes and ketones, leading to unpleasant smell and taste known as rancidity.
Q9. What is the change associated with rancid food?
Change in smell and tasteRancid food develops a sharp, unpleasant odor (often described as “off” or sour) and a bitter or metallic taste, making it unsuitable for consumption.
Q10. What are substances called that prevent oxidation in food?
AntioxidantsAntioxidants are compounds that inhibit oxidation by being oxidized themselves, protecting fats and oils from becoming rancid. Examples include vitamin C, vitamin E, and BHA.
Q11. How does keeping food in airtight containers help?
It slows down oxidation.Airtight containers prevent oxygen from reaching the food, thereby reducing the rate of oxidation and delaying rancidity.
Q12. Which gas do chips manufacturers flush into bags to prevent oxidation?
NitrogenNitrogen is an inert gas that displaces oxygen inside the packet, creating an oxygen-free environment that prevents oxidation of the fats in chips.
Q13. What is the primary reason for flushing chips bags with nitrogen?
To prevent chips from getting oxidisedBy removing oxygen and replacing it with nitrogen, the oxidation reaction that leads to rancidity is effectively prevented, keeping chips fresh for longer.
Q14. According to the summary, what must a complete chemical equation represent?
The reactants, products, and their physical statesA complete chemical equation shows what substances react (reactants), what substances are formed (products), and their physical states using symbols like (s), (l), (g), (aq).
Q15. Why must a chemical equation always be balanced?
So that the number of atoms of each type is the same on both sidesBalancing obeys the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction.
Q16. In which reaction do two or more substances combine to form a new single substance?
Combination reactionA combination reaction (also called synthesis) follows the pattern A + B → C, where multiple reactants form one product. Example: 2Mg + O₂ → 2MgO.
Q17. What type of reaction is the opposite of a combination reaction?
DecompositionWhile combination joins substances together, decomposition breaks a single compound into simpler substances (C → A + B), making them reverse processes.
Q18. In a decomposition reaction, what happens?
A single substance decomposes into two or more substances.Decomposition reactions involve breaking down one reactant into multiple products, often requiring energy input in the form of heat, light, or electricity.
Q19. What are reactions called in which heat is given out along with the products?
Exothermic“Exo” means outward, “thermic” means heat. Exothermic reactions release heat energy to the surroundings, making the container feel warm or hot.
Q20. What are reactions called in which heat is absorbed?
Endothermic“Endo” means inward. Endothermic reactions absorb heat from the surroundings, causing the container to feel cold. Decomposition reactions are often endothermic.
Q21. What occurs in a displacement reaction?
An element displaces another element from its compound.In a single displacement reaction, a more reactive element replaces a less reactive element from its compound, following the pattern A + BC → AC + B.
Q22. What is exchanged in a double displacement reaction?
Two different atoms or groups of atoms (ions)Double displacement involves exchange of ions between two reactants, following AB + CD → AD + CB.
Q23. What do precipitation reactions produce?
Insoluble saltsA precipitation reaction is a type of double displacement where one product is an insoluble salt that separates from the solution as a solid precipitate.
Q24. According to the summary, what is oxidation defined as?
Gain of oxygen or loss of hydrogenIn traditional terms, oxidation is the gain of oxygen (e.g., rusting) or loss of hydrogen. In modern terms, it is loss of electrons.
Q25. According to the summary, what is reduction defined as?
Loss of oxygen or gain of hydrogenReduction is the opposite of oxidation: loss of oxygen (e.g., metal ores being reduced to metals) or gain of hydrogen.
Q26. What happens to silver chloride when placed in sunlight?
It turns grey.White silver chloride (AgCl) decomposes in sunlight to form grey silver metal and chlorine gas: 2AgCl → 2Ag (grey) + Cl₂.
Q27. What causes the decomposition of silver chloride?
Light (Sunlight)This is a photolytic decomposition reaction, where light energy (photons) provides the activation energy to break down silver chloride.
Q28. What are the products of the decomposition of silver chloride in sunlight?
Silver and chlorine gasThe balanced equation is 2AgCl (white) —sunlight→ 2Ag (grey) + Cl₂ (gas). The silver metal formed gives the grey color.
Q29. Which compound behaves similarly to silver chloride in sunlight?
Silver bromideSilver bromide (AgBr) also decomposes in light to form silver metal and bromine gas. It is even more light-sensitive than AgCl.
Q30. Where is the decomposition reaction of silver salts used?
In black and white photographyPhotographic films are coated with silver bromide, which decomposes when exposed to light, creating a latent image that is developed into a photograph.
Q31. What form of energy causes the decomposition of silver chloride and silver bromide?
Light energyThese are photolytic decomposition reactions, specifically triggered by light energy (photons) rather than heat or electricity.
Q32. Decomposition reactions require energy in the form of:
Heat, light, or electricityDepending on the compound, decomposition can be thermal (heat), photolytic (light), or electrolytic (electricity).
Q33. What type of reaction is the decomposition of silver chloride in terms of heat change?
EndothermicDecomposition reactions generally require energy input to break chemical bonds, making them endothermic. The energy is absorbed as light in this case.
Q34. In the reaction Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s), what is observed?
The blue color of copper sulfate fades, and the nail gets a brownish coating.Iron displaces copper from blue CuSO₄ solution. As Cu²⁺ ions are removed, blue color fades; displaced copper metal deposits as a brownish layer on the iron nail.
Q35. What type of reaction is Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)?
DisplacementThis is a single displacement reaction where iron (more reactive) displaces copper (less reactive) from copper sulphate solution.
Q36. In the displacement reaction, which element is displaced by iron?
CopperIron replaces copper in copper sulphate. Copper ions (Cu²⁺) are reduced to copper metal, while iron is oxidized to Fe²⁺ ions.
Q37. Which of the following is another example of a displacement reaction?
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)Zinc displaces copper from copper sulphate because zinc is more reactive than copper, following the same pattern as the iron-copper reaction.
Q38. Why can zinc displace copper from its compound?
Zinc is more reactive than copper.In the reactivity series, zinc is above copper. A more reactive metal can displace a less reactive metal from its salt solution.
Q39. What is the color of copper sulfate solution?
BlueHydrated copper(II) sulfate (CuSO₄·5H₂O) forms a characteristic blue solution due to the presence of water molecules in the copper complex.
Q40. What is the brownish coating that forms on the iron nail?
Copper metalThe displaced copper is deposited as reddish-brown copper metal on the surface of the iron nail, not as copper oxide or rust.
Q41. What is the energy requirement for endothermic reactions?
They absorb heat.Endothermic reactions require continuous absorption of heat from surroundings to proceed, making the reaction mixture feel cooler.
Q42. Based on the text, what is the result of mixing barium hydroxide and ammonium chloride likely to be?
An endothermic reaction (test tube feels cold)Ba(OH)₂·8H₂O + 2NH₄Cl → BaCl₂ + 2NH₃ + 10H₂O is strongly endothermic, causing temperature to drop significantly (test tube becomes cold to touch).
Q43. What is the main takeaway regarding the energy for decomposition reactions?
They always require an input of energy.Decomposition breaks chemical bonds, which requires energy. This energy can come from heat, light, or electricity, but must be supplied.
Q44. In the context of the text, what does “tarnished” mean for metals?
Losing luster and developing a coatingTarnishing is surface corrosion where metals like silver and copper lose their shine and form a dull, discolored layer due to reaction with air compounds.
Q45. What is the common factor between rancidity and corrosion?
Both are caused by oxidation reactions.Rusting of iron (corrosion) and spoiling of fats (rancidity) are both oxidation reactions involving reaction with atmospheric oxygen.
Q46. According to the learnt points, what is always true for a balanced chemical equation?
The number of atoms of each element is the same on both sides.This is the Law of Conservation of Matter – atoms are neither created nor destroyed, only rearranged in chemical reactions.
Q47. What is the visual evidence that a displacement reaction has occurred between iron and copper sulfate?
Change in color of the solution and the metalThe blue solution fades (turning greenish due to Fe²⁺ ions), and the iron nail acquires a brownish copper coating – both visible changes.
Q48. What is the purpose of adding antioxidants to food?
To prevent oxidation and rancidityAntioxidants like BHA, BHT, and vitamin E are added to fatty foods to prevent oxidative deterioration, extending shelf life.
Q49. Which of the following is NOT listed as a form of energy that can cause decomposition?
SoundDecomposition reactions can be triggered by heat (thermal), light (photolytic), or electricity (electrolytic), but not by sound energy.
Q50. Based on the summary, which statement correctly describes a double displacement reaction?
Two compounds exchange ions to form two new compounds.Double displacement follows AB + CD → AD + CB, where ions swap partners between the two reactant compounds.