Q1. Why must a magnesium ribbon be cleaned before burning in air?
a) To increase its weight
b) To remove the protective layer of oxide on its surface
c) To make it look shiny
d) To prevent it from burning
Answer: b) To remove the protective layer of oxide on its surface
Explanation: A magnesium ribbon is cleaned before burning to remove the protective layer of magnesium oxide on its surface. This ensures that the ribbon can react more readily with oxygen in the air, allowing the combustion reaction to proceed efficiently.
Q2. What is the main objective of balancing a chemical equation?
a) To ensure that the reaction proceeds at a faster rate
b) To satisfy the law of conservation of mass
c) To use up all reactants
d) To produce more products
Answer: b) To satisfy the law of conservation of mass
Explanation: Balancing a chemical equation is crucial to satisfy the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. This ensures that the number of atoms for each element is the same on both sides of the equation.
Q3. In the reaction between sodium sulphate and barium chloride, what is formed?
a) A yellow precipitate
b) A grey precipitate
c) A white precipitate of barium sulphate
d) A pink precipitate
Answer: c) A white precipitate of barium sulphate
Explanation: When sodium sulphate and barium chloride react, a white precipitate of barium sulphate is formed. This reaction is an example of a precipitation reaction, where two soluble salts react to form an insoluble salt, demonstrating a double displacement reaction.
Q4. What type of reaction is Fe + H2O → Fe3O4 + H2?
a) Decomposition reaction
b) Displacement reaction
c) Combination reaction
d) Redox reaction
Answer: d) Redox reaction
Explanation: The reaction between iron (Fe) and water (H2O) to produce iron oxide (Fe3O4) and hydrogen gas (H2) is a redox reaction. In this process, iron is oxidized, and water is reduced, showcasing the transfer of electrons between reactants.
Q5. Why is respiration considered an exothermic reaction?
a) It absorbs energy from the surroundings
b) It requires external heat to proceed
c) It releases energy to the surroundings
d) It occurs without any change in energy
Answer: c) It releases energy to the surroundings
Explanation: Respiration is considered an exothermic reaction because it releases energy to the surroundings. During respiration, glucose reacts with oxygen to produce carbon dioxide and water, releasing energy that is used by organisms for various biological processes.
Q6. Which reaction is categorized as a thermal decomposition reaction?
a) 2H2O(l) → 2H2(g) + O2(g)
b) 2AgBr(s) → 2Ag(s) + Br2(g)
c) 2AgCl(s) → 2Ag(s) + Cl2(g)
d) CaCO3(s) → CaO(s) + CO2(g)
Answer: d) CaCO3(s) → CaO(s) + CO2(g)
Explanation: The decomposition of calcium carbonate (CaCO3) into calcium oxide (CaO) and carbon dioxide (CO2) when heated is an example of a thermal decomposition reaction. This type of reaction involves the breakdown of a compound into two or more components by heat.
Q7. What change is observed when an iron nail is dipped in copper sulphate solution for about 30 minutes?
a) The color of the copper sulphate solution remains the same, and the iron nail becomes silver.
b) The iron nail gains mass, and the copper sulphate solution becomes colorless.
c) The color of the copper sulphate solution fades, and the iron nail gets coated with a red-brown substance.
d) No change is observed in either the iron nail or the copper sulphate solution.
Answer: c) The color of the copper sulphate solution fades, and the iron nail gets coated with a red-brown substance.
Explanation: When an iron nail is dipped in copper sulphate solution, a displacement reaction occurs. Iron (more reactive) displaces copper from its solution, leading to the fading color of copper sulphate solution and the deposition of copper on the iron nail, which appears as a red-brown coating.
Q8. What is produced when sodium reacts with water?
a) Sodium hydroxide and hydrogen gas
b) Sodium oxide and water
c) Sodium chloride and oxygen gas
d) Sodium bicarbonate and hydrogen gas
Answer: a) Sodium hydroxide and hydrogen gas
Explanation: When sodium reacts with water, it forms sodium hydroxide and releases hydrogen gas. This reaction is highly exothermic, and care should be taken due to the vigorous reaction and potential for the hydrogen gas to ignite.
Q9. What signifies a double displacement reaction?
a) Exchange of atoms takes place.
b) Exchange of ions between the reactants.
c) Only a single product is formed.
d) Reactants combine without any exchange.
Answer: b) Exchange of ions between the reactants.
Explanation: A double displacement reaction is characterized by the exchange of ions between the reactants to form new products. This type of reaction often results in the formation of a precipitate, a gas, or a water molecule as a product.
Q10. Which of the following statements accurately describes an exothermic reaction?
a) Absorbs heat from the surroundings, making the environment cooler.
b) Releases heat into the surroundings, making the environment warmer.
c) Occurs without any exchange of heat with the surroundings.
d) Requires an external source of heat to proceed.
Answer: b) Releases heat into the surroundings, making the environment warmer.
Explanation: An exothermic reaction is one that releases heat into the surroundings, resulting in an increase in temperature around the reaction site. These reactions can often be felt as warmth or seen as heat being emitted.
Q11. Which compound acts as a reducing agent in the recovery of silver from silver nitrate solution using copper metal?
a) Silver nitrate
b) Copper
c) Silver
d) Nitric acid
Answer: b) Copper
Explanation: In the recovery of silver from silver nitrate solution, copper acts as a reducing agent. Copper metal displaces silver from the silver nitrate solution, resulting in the formation of copper nitrate and pure silver. This displacement reaction showcases the reduction of silver ions to metallic silver by copper.
Q12. What happens to the mass of reactants and products in a chemical reaction according to the law of conservation of mass?
a) The mass of products is always greater than the mass of reactants.
b) The mass of reactants is converted into energy according to E=mc^2.
c) The total mass of the reactants equals the total mass of the products.
d) The mass of products is lost to the surroundings as heat.
Answer: c) The total mass of the reactants equals the total mass of the products.
Explanation: According to the law of conservation of mass, the total mass of the reactants in a chemical reaction equals the total mass of the products. This law highlights that mass is neither created nor destroyed in a chemical reaction, ensuring the mass balance of a chemical equation.
Q13. What observation confirms a chemical reaction involving calcium hydroxide and carbon dioxide?
a) The mixture turns blue, indicating water formation.
b) A decrease in temperature is observed, showing an endothermic reaction.
c) Formation of a white precipitate, indicating the production of calcium carbonate.
d) Release of a gas that turns lime water milky, indicating oxygen release.
Answer: c) Formation of a white precipitate, indicating the production of calcium carbonate.
Explanation: When calcium hydroxide reacts with carbon dioxide, a white precipitate of calcium carbonate is formed. This reaction is utilized in the process of whitewashing, where calcium hydroxide reacts with carbon dioxide in the air over time to form a hard layer of calcium carbonate on walls.
Q14. How is manganese obtained from manganese dioxide in the laboratory?
a) By heating manganese dioxide with a strong acid.
b) By electrolysis of manganese dioxide in an aqueous solution.
c) By reduction of manganese dioxide with a suitable reducing agent like aluminum powder.
d) By direct exposure of manganese dioxide to sunlight.
Answer: c) By reduction of manganese dioxide with a suitable reducing agent like aluminum powder.
Explanation: Manganese can be obtained from manganese dioxide by reduction using a suitable reducing agent like aluminum powder. This process involves a thermite reaction, where aluminum reduces manganese dioxide to manganese by taking away the oxygen.
Q15. During the thermal decomposition of lead nitrate, what are the products formed?
a) Lead, nitrogen gas, and oxygen gas.
b) Lead oxide, nitrogen dioxide, and oxygen gas.
c) Lead sulfate, nitric acid, and water vapor.
d) Lead carbonate, nitrogen monoxide, and carbon dioxide.
Answer: b) Lead oxide, nitrogen dioxide, and oxygen gas.
Explanation: The thermal decomposition of lead nitrate results in the formation of lead oxide, nitrogen dioxide, and oxygen gas. This reaction is an example of a thermal decomposition reaction, where heat causes a compound to break down into simpler substances.
Q16. What is observed when dilute hydrochloric acid is added to iron fillings?
a) The solution turns blue, and a gas is evolved.
b) Hydrogen gas and iron chloride are produced.
c) No reaction takes place.
d) Iron hydroxide is precipitated.
Answer: b) Hydrogen gas and iron chloride are produced.
Explanation: When dilute hydrochloric acid is added to iron fillings, a reaction occurs that produces iron chloride and hydrogen gas. This reaction is an example of a single displacement reaction where hydrogen in the acid is displaced by iron.
Q17. Which one of the following is not a correct statement regarding the need to balance chemical equations?
a) To reflect the law of conservation of mass.
b) To predict the amount of products formed.
c) To indicate the speed of the reaction.
d) To show the stoichiometry of the reaction.
Answer: c) To indicate the speed of the reaction.
Explanation: Balancing chemical equations does not indicate the speed of the reaction. It is necessary to reflect the law of conservation of mass, predict the amount of products formed, and show the stoichiometry of the reaction. The rate of the reaction is determined by other factors, such as concentration, temperature, and presence of catalysts.
Q18. What results from the reaction of sodium hydroxide and hydrochloric acid?
a) Sodium chloride and hydrogen gas.
b) Sodium chloride and oxygen gas.
c) Sodium chloride and water.
d) Sodium bicarbonate and water.
Answer: c) Sodium chloride and water.
Explanation: The reaction between sodium hydroxide and hydrochloric acid is a neutralization reaction that produces sodium chloride (common salt) and water. This reaction exemplifies how acids and bases react to form salt and water.
Q19. What is the result of the reaction between barium chloride and sodium sulphate?
a) Formation of sodium chloride and barium sulphate
b) Production of barium carbonate and sodium nitrate
c) Emission of chlorine gas
d) Release of hydrogen gas
Answer: a) Formation of sodium chloride and barium sulphate
Explanation: The reaction between barium chloride and sodium sulphate is a classic example of a double displacement reaction, leading to the formation of barium sulphate, a white precipitate, and sodium chloride dissolved in the solution.
Q20. Which of the following is an example of an endothermic reaction?
a) Combustion of natural gas
b) Thermal decomposition of potassium chlorate
c) Neutralization of hydrochloric acid and sodium hydroxide
d) Respiration in humans
Answer: b) Thermal decomposition of potassium chlorate
Explanation: The thermal decomposition of potassium chlorate is an endothermic reaction because it requires the absorption of heat to break down potassium chlorate into potassium chloride and oxygen gas. Endothermic reactions absorb energy from their surroundings.
Q21. What is observed when silver chloride is exposed to sunlight?
a) It dissolves completely, leaving no residue
b) It changes from white to grey due to the formation of silver
c) It explodes releasing chlorine gas
d) It turns into liquid silver
Answer: b) It changes from white to grey due to the formation of silver
Explanation: Silver chloride decomposes under sunlight to form silver and chlorine gas. This change causes the color of silver chloride to turn from white to grey, demonstrating a photochemical decomposition reaction.
Q22: How does the principle of conservation of mass apply to the reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) to form sodium chloride (NaCl) and water (H2O)?
a) The mass of NaOH and HCl used equals the mass of NaCl and H2O produced.
b) The mass of NaCl produced is greater than the mass of NaOH and HCl used.
c) The reaction does not conserve mass because it produces gas.
d) The mass of NaOH and HCl disappears after the reaction.
Answer: a) The mass of NaOH and HCl used equals the mass of NaCl and H2O produced.
Explanation: According to the law of conservation of mass, the total mass of reactants in a chemical reaction must equal the total mass of the products. In the neutralization reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl), which produces sodium chloride (NaCl) and water (H2O), the mass of the reactants (NaOH and HCl) before the reaction is equal to the mass of the products (NaCl and H2O) after the reaction. This principle demonstrates that mass is neither created nor destroyed in a chemical reaction.
Q23. In the context of oxidation and reduction, which of the following is true?
a) Oxidation involves gain of electrons, and reduction involves loss of electrons.
b) Oxidation is the loss of oxygen, and reduction is the gain of oxygen.
c) Oxidation involves loss of electrons, and reduction involves gain of electrons.
d) Oxidation and reduction are processes that can occur independently of each other.
Answer: c) Oxidation involves loss of electrons, and reduction involves gain of electrons.
Explanation: In redox reactions, oxidation is defined as the loss of electrons, whereas reduction is the gain of electrons. These processes are complementary to each other and occur simultaneously in a redox reaction.
Q24. What prevents the rusting of iron?
a) Keeping it in an oxygen-free environment
b) Coating it with zinc
c) Exposing it to more moisture
d) Sprinkling iron filings over it
Answer: b) Coating it with zinc
Explanation: Coating iron with zinc, a process known as galvanization, prevents rusting by providing a protective layer that prevents oxygen and water from reaching the iron surface. Zinc also acts as a sacrificial anode, corroding in place of the iron.
Q25. Which of the following statements accurately describes the action of antioxidants in food preservation?
a) Antioxidants accelerate the oxidation of fats and oils to improve taste.
b) Antioxidants remove oxygen from the environment, making it unsuitable for microbial growth.
c) Antioxidants prevent the oxidation of fats and oils, delaying rancidity.
d) Antioxidants convert oxidized molecules into water and carbon dioxide.
Answer: c) Antioxidants prevent the oxidation of fats and oils, delaying rancidity.
Explanation: Antioxidants are substances that prevent the oxidation of fats and oils in food, thereby delaying the onset of rancidity. Oxidation of fats and oils can lead to off-flavors and spoilage, and antioxidants help in preserving the quality and shelf-life of food products.
Q26. Which of the following is a characteristic of a displacement reaction?
a) It involves the exchange of ions between two compounds.
b) It occurs only in liquid solutions.
c) A more reactive element displaces a less reactive element from its compound.
d) It results exclusively in the formation of gases.
Answer: c) A more reactive element displaces a less reactive element from its compound.
Explanation: In a displacement reaction, a more reactive element displaces a less reactive element from its compound, resulting in the formation of a new compound. This type of reaction is commonly observed in reactions involving metals and their salts.
Q27. During electrolysis of water, what is observed at the cathode and anode?
a) Oxygen gas at the cathode and hydrogen gas at the anode.
b) Hydrogen gas at both the cathode and anode.
c) Hydrogen gas at the cathode and oxygen gas at the anode.
d) Water vapor at the cathode and oxygen gas at the anode.
Answer: c) Hydrogen gas at the cathode and oxygen gas at the anode.
Explanation: During the electrolysis of water, hydrogen gas is produced at the cathode (negative electrode) due to the reduction of water, and oxygen gas is produced at the anode (positive electrode) due to the oxidation of water. This process demonstrates the decomposition of water into its elemental components.
Q28. What does the phenomenon of corrosion typically involve?
a) The physical dismantling of a metal through repeated mechanical stress.
b) The decoration of metal surfaces with intricate designs.
c) The chemical reaction of a metal with substances in its environment, leading to deterioration.
d) The enhancement of metal strength through heat treatment.
Answer: c) The chemical reaction of a metal with substances in its environment, leading to deterioration.
Explanation: Corrosion is a chemical process that involves the reaction of a metal with substances present in its environment, such as oxygen and moisture, leading to the deterioration of the metal. This process can result in significant damage to metal structures and objects.
Q29. What is the product when magnesium reacts with hydrochloric acid?
a) Magnesium chloride and hydrogen gas
b) Magnesium hydroxide and chlorine gas
c) Magnesium oxide and water
d) Magnesium sulfate and hydrogen peroxide
Answer: a) Magnesium chloride and hydrogen gas
Explanation: When magnesium reacts with hydrochloric acid, magnesium chloride and hydrogen gas are produced. This reaction is an example of a single displacement reaction, where magnesium displaces hydrogen from hydrochloric acid.
Q30. Which reaction is classified as an exothermic reaction?
a) Photosynthesis in plants
b) Melting of ice cubes
c) Combustion of methane gas
d) Evaporation of water
Answer: c) Combustion of methane gas
Explanation: The combustion of methane gas is an exothermic reaction because it releases a significant amount of energy in the form of heat and light. Exothermic reactions are characterized by the release of energy to the surroundings, which can be observed as warmth or flames in the case of combustion.
Q31. What happens when zinc granules are added to copper sulfate solution?
a) The blue color of the solution fades and copper granules are deposited.
b) The solution turns green and zinc sulfate is formed.
c) No reaction occurs because zinc is less reactive than copper.
d) The solution becomes colorless and zinc oxide forms.
Answer: a) The blue color of the solution fades and copper granules are deposited.
Explanation: When zinc granules are added to a copper sulfate solution, a displacement reaction occurs. Zinc, being more reactive than copper, displaces copper from its sulfate compound. This results in the fading of the blue color of the solution due to the formation of zinc sulfate, and copper is deposited as granules.
Q32. In the reaction 2KClO3 → 2KCl + 3O2, what is the role of KClO3?
a) Reducing agent
b) Oxidizing agent
c) Catalyst
d) Solvent
Answer: b) Oxidizing agent
Explanation: In the decomposition of potassium chlorate (KClO3) to form potassium chloride (KCl) and oxygen gas (O2), potassium chlorate acts as an oxidizing agent. It provides oxygen for reactions, facilitating processes that require the removal of electrons from other substances.
Q33. Why is painting used as a method to prevent rusting of iron?
a) To absorb moisture from the surroundings
b) To physically separate the iron surface from atmospheric oxygen and moisture
c) To react chemically with rust and convert it back to iron
d) To make the surface look aesthetically pleasing only
Answer: b) To physically separate the iron surface from atmospheric oxygen and moisture
Explanation: Painting is used as a method to prevent rusting of iron by creating a physical barrier that separates the iron surface from atmospheric oxygen and moisture. Rusting is an oxidation reaction that requires the presence of both oxygen and water. By blocking these elements, painting effectively prevents rust.
Q34. What is observed when a solution of barium chloride reacts with a solution of sodium sulfate?
a) A green precipitate forms due to the production of barium sulfate.
b) A white precipitate of barium sulfate forms, indicating a double displacement reaction.
c) The solution bubbles and releases hydrogen gas.
d) The mixture turns purple as an indicator of a chemical reaction.
Answer: b) A white precipitate of barium sulfate forms, indicating a double displacement reaction.
Explanation: When solutions of barium chloride and sodium sulfate are mixed, a white precipitate of barium sulfate is formed. This reaction is an example of a double displacement reaction, where the cations and anions of two different compounds swap places, resulting in the formation of an insoluble salt.
Q35. What is the product of the neutralization reaction between hydrochloric acid and sodium hydroxide?
a) Sodium chloride and oxygen gas
b) Sodium chloride and water
c) Sodium bicarbonate and hydrochloric acid
d) Chlorine gas and water
Answer: b) Sodium chloride and water
Explanation: The neutralization reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) produces sodium chloride (NaCl), a salt, and water (H2O). This type of reaction typically involves an acid and a base reacting to form a salt and water.
Q36. What signifies a chemical change has occurred during the cooking of food?
a) The food becomes inedible.
b) Physical state changes from solid to liquid.
c) New substances are formed with different properties.
d) The food absorbs moisture from the air.
Answer: c) New substances are formed with different properties.
Explanation: The cooking of food involves chemical changes where new substances are formed with different properties from the original ingredients. These changes are often evidenced by changes in color, flavor, texture, and nutritional content, indicating that chemical reactions have taken place.
Q37. Which gas is evolved when dilute hydrochloric acid reacts with zinc metal?
a) Oxygen gas
b) Chlorine gas
c) Hydrogen gas
d) Carbon dioxide gas
Answer: c) Hydrogen gas
Explanation: When dilute hydrochloric acid reacts with zinc metal, hydrogen gas is evolved. This reaction is an example of a single displacement reaction where zinc displaces hydrogen from hydrochloric acid, forming zinc chloride and releasing hydrogen gas.
Q38. What is the primary reason for using a catalyst in a chemical reaction?
a) To increase the yield of the product
b) To act as a reactant in the reaction
c) To decrease the reaction temperature
d) To speed up the reaction without being consumed
Answer: d) To speed up the reaction without being consumed
Explanation: A catalyst is used in a chemical reaction primarily to speed up the reaction without being consumed by the reaction itself. Catalysts work by providing an alternative pathway for the reaction that has a lower activation energy, thereby increasing the rate of the reaction.
Q39. What happens when light is passed through a solution of silver chloride?
a) It dissolves completely, leaving a clear solution.
b) It changes from white to black, indicating the formation of elemental silver.
c) It precipitates out as silver nitrate.
d) No visible change occurs.
Answer: b) It changes from white to black, indicating the formation of elemental silver.
Explanation: When light is passed through a solution of silver chloride, it causes the silver chloride to decompose into elemental silver and chlorine gas. This process is used in photographic films and paper, where the silver chloride turns from white to black, indicating the formation of elemental silver.
Q40. What is observed when carbon dioxide gas is passed through lime water?
a) The lime water turns milky due to the formation of calcium carbonate.
b) The solution becomes colorless, indicating the complete absorption of carbon dioxide.
c) Bubbles of oxygen gas are formed.
d) The lime water turns pink, indicating the presence of an acid.
Answer: a) The lime water turns milky due to the formation of calcium carbonate.
Explanation: When carbon dioxide gas is passed through lime water, it reacts with the calcium hydroxide in the lime water to form calcium carbonate, which is insoluble in water and causes the lime water to turn milky. This is a classic test for the presence of carbon dioxide.
Q41. What is formed when ethanoic acid reacts with sodium carbonate?
a) Sodium ethanoate, carbon dioxide, and water
b) Sodium chloride, carbon dioxide, and water
c) Sodium bicarbonate and ethanoic acid
d) Ethanol, sodium chloride, and carbon dioxide
Answer: a) Sodium ethanoate, carbon dioxide, and water
Explanation: When ethanoic acid reacts with sodium carbonate, sodium ethanoate, carbon dioxide, and water are formed. This reaction is an example of an acid-base reaction, where an acid reacts with a carbonate to produce a salt, carbon dioxide, and water.
Q42. In an exothermic reaction, where does the energy released go?
a) It is absorbed by the reactants, increasing their potential energy.
b) It is used to break the bonds in the reactants.
c) It is released to the surroundings, often observed as heat.
d) It converts into mass, following the principle of mass-energy equivalence.
Answer: c) It is released to the surroundings, often observed as heat.
Explanation: In an exothermic reaction, the energy released during the reaction goes to the surroundings, which is often observed as heat. This release of energy is due to the formation of products that have lower energy than the reactants, and the excess energy is given off as heat.
Q43. Which of the following is true for a balanced chemical equation?
a) It indicates that the reaction spontaneously occurs.
b) It shows the physical states of the reactants and products.
c) It ensures that mass is conserved by having an equal number of atoms for each element on both sides of the equation.
d) It predicts the speed at which the reaction proceeds.
Answer: c) It ensures that mass is conserved by having an equal number of atoms for each element on both sides of the equation.
Explanation: A balanced chemical equation ensures that the law of conservation of mass is satisfied by having an equal number of atoms for each element involved in the reaction on both the reactant and product sides. This is crucial for accurately representing the chemical reaction.
Q44. Which process is used to separate a mixture of ink?
a) Filtration
b) Distillation
c) Chromatography
d) Crystallization
Answer: c) Chromatography
Explanation: Chromatography is a technique used to separate and identify the different components of a mixture, such as ink. It relies on the different speeds at which the components move through a medium under the influence of a solvent, allowing for their separation and analysis.
Q45. What type of reaction is photosynthesis?
a) Decomposition
b) Displacement
c) Endothermic
d) Exothermic
Answer: c) Endothermic
Explanation: Photosynthesis is an endothermic reaction because it requires the absorption of energy from sunlight to convert carbon dioxide and water into glucose and oxygen. The energy absorbed is stored in the chemical bonds of the glucose molecules.
Q46. What is the primary purpose of galvanizing iron?
a) To enhance its electrical conductivity
b) To improve its appearance with a shiny finish
c) To protect it from rusting by coating it with a layer of zinc
d) To increase its weight for construction purposes
Answer: c) To protect it from rusting by coating it with a layer of zinc
Explanation: Galvanizing iron involves coating it with a layer of zinc to protect it from rusting. Zinc acts as a protective barrier and also as a sacrificial anode, corroding in preference to the iron and thereby providing long-term protection against corrosion.
Q47. In which situation is the law of conservation of energy demonstrated?
a) Melting ice without any change in temperature
b) A ball rolling down a hill and gaining speed
c) Water evaporating from a pond
d) Burning a piece of wood completely
Answer: d) Burning a piece of wood completely
Explanation: The burning of a piece of wood demonstrates the law of conservation of energy, where the chemical potential energy stored in the wood is converted into thermal energy (heat) and light energy as it burns. The total amount of energy before and after the reaction remains constant, illustrating the conservation of energy.
Q48. What occurs when potassium iodide solution is added to lead(II) nitrate solution?
a) A colorless solution is formed.
b) A yellow precipitate of lead(II) iodide is formed.
c) Bubbles of hydrogen gas are released.
d) The temperature of the solution significantly increases.
Answer: b) A yellow precipitate of lead(II) iodide is formed.
Explanation: When potassium iodide solution is mixed with lead(II) nitrate solution, a yellow precipitate of lead(II) iodide is formed. This is a result of a double displacement reaction, where lead(II) and iodide ions exchange partners to form the insoluble lead(II) iodide.
Q49. Which substance acts as the reducing agent in the thermite reaction between iron(III) oxide and aluminum?
a) Iron(III) oxide
b) Aluminum
c) Iron
d) Oxygen
Answer: b) Aluminum
Explanation: In the thermite reaction, aluminum acts as the reducing agent. It donates electrons to iron(III) oxide, reducing it to molten iron, while aluminum itself gets oxidized to aluminum oxide. This highly exothermic reaction is used in welding and metal cutting processes.
Q50. What is the result of mixing acetic acid with sodium bicarbonate (baking soda)?
a) Formation of sodium acetate, carbon dioxide, and water
b) Production of sodium chloride and hydrogen gas
c) No reaction occurs
d) Formation of ethanoic acid and sodium carbonate
Answer: a) Formation of sodium acetate, carbon dioxide, and water
Explanation: When acetic acid reacts with sodium bicarbonate (baking soda), it produces sodium acetate, carbon dioxide, and water. This reaction is a typical acid-base reaction that results in the effervescence due to the release of carbon dioxide gas.
Q51. How does increasing the surface area of reactants affect the rate of a chemical reaction?
a) It has no effect on the reaction rate
b) It decreases the reaction rate
c) It increases the reaction rate
d) It changes the direction of the reaction
Answer: c) It increases the reaction rate
Explanation: Increasing the surface area of reactants increases the rate of a chemical reaction by providing more area for collisions between reactant molecules. This increase in collision frequency leads to a faster reaction rate.
Q52. What is the primary function of electrolytes in electrolysis?
a) To decrease the conductivity of the solution
b) To increase the melting point of the compound
c) To act as a source of ions for conducting electricity
d) To act as a catalyst and speed up the reaction without participating
Answer: c) To act as a source of ions for conducting electricity
Explanation: In electrolysis, electrolytes function as a source of ions that conduct electricity through the solution. These ions move towards the electrodes, where they undergo oxidation or reduction, enabling the electrolytic process.
Q53. What change occurs when quicklime (calcium oxide) is added to water?
a) The solution turns acidic
b) A precipitate is formed
c) It results in the formation of slaked lime (calcium hydroxide) and heat
d) Quicklime dissolves, forming a colorless solution
Answer: c) It results in the formation of slaked lime (calcium hydroxide) and heat
Explanation: When quicklime (calcium oxide) is added to water, it reacts vigorously to form slaked lime (calcium hydroxide) and releases a significant amount of heat. This exothermic reaction is utilized in various applications, including the preparation of lime mortar.
Q54. What indicates that a chemical reaction has reached equilibrium?
a) The reactants are completely consumed
b) The rate of the forward reaction equals the rate of the reverse reaction
c) The products revert entirely back to reactants
d) The temperature of the reaction mixture steadily increases
Answer: b) The rate of the forward reaction equals the rate of the reverse reaction
Explanation: A chemical reaction reaches equilibrium when the rate of the forward reaction equals the rate of the reverse reaction. At this point, the concentrations of reactants and products remain constant over time, indicating a dynamic balance between the forward and reverse processes.