Chemical Reactions And Equations - Practice Test, Class 10 Science - Class 10 MCQ

• Reduction: In this reaction, copper oxide (CuO) is reduced to copper metal (Cu). Reduction is the gain of electrons by a substance. In this case, copper oxide gains electrons from hydrogen to form copper metal.

• Endothermic: Endothermic reactions absorb heat from their surroundings. In the hydrolysis of water, energy is required to break the bonds between the hydrogen and oxygen atoms in water molecules, making it an endothermic reaction.



• Decomposition: Decomposition reactions involve breaking down a compound into simpler substances. In the hydrolysis of water, water molecules are broken down into hydrogen and oxygen molecules, making it a decomposition reaction.



• Both (a) and (b): Since the hydrolysis of water is both endothermic and a decomposition reaction, the correct answer is both (a) and (b).



• Combination: Combination reactions involve the combination of two or more substances to form a new compound. The hydrolysis of water does not involve the combination of different substances, so it is not a combination reaction.

Therefore, the hydrolysis of water is classified as both an endothermic and decomposition reaction, making the correct answer C: Both (a) and (b).

• Proteins: Amino acids are the building blocks of proteins. When we consume protein-rich foods, our body breaks down the proteins into individual amino acids through the process of digestion.


• Digestive Enzymes: Enzymes in our digestive system break down the protein molecules into amino acids, which can then be absorbed into the bloodstream and used for various functions in the body.


• Essential Amino Acids: Our body needs a specific set of amino acids, known as essential amino acids, which cannot be produced by the body itself. These must be obtained through our diet by consuming protein-rich foods.


• Role of Amino Acids: Amino acids play crucial roles in various physiological processes, such as building and repairing tissues, supporting immune function, and producing enzymes and hormones.

• Therefore, amino acids are formed by the decomposition of proteins in our diet, highlighting the importance of consuming an adequate amount of protein to meet our body's amino acid requirements.

• Correct Answer: Calcium oxide

• Quick lime is chemically known as Calcium oxide.


• It is a white, caustic, alkaline crystalline solid at room temperature.


• When water is added to quick lime, it undergoes a vigorous exothermic reaction to produce Calcium hydroxide.


• Calcium oxide is commonly used in construction, agriculture, and chemical industries.

• Definition: Loss of electrons is known as oxidation.


• Explanation: When a substance loses electrons during a chemical reaction, it is said to be oxidized. This process results in an increase in the oxidation number of the substance.


• Example: One common example of oxidation is the reaction of iron with oxygen to form rust. In this reaction, iron loses electrons to oxygen, leading to the formation of iron oxide.


• Significance: Oxidation reactions play a crucial role in many biological processes, such as cellular respiration, where glucose is oxidized to produce energy.

• Bonds: Chemical reactions involve the breaking and formation of chemical bonds between atoms. Bonds are either broken or formed during a chemical reaction.


• Breaking of Bonds: In a chemical reaction, existing bonds between atoms in the reactants are broken. This requires an input of energy to break the bonds.


• Formation of Bonds: Simultaneously, new bonds are formed between atoms in the products of the reaction. This release of energy as new bonds are formed.


• Energy Change: The difference between the energy required to break the bonds and the energy released when new bonds are formed determines the overall energy change of the reaction.


• Law of Conservation of Mass: The total mass of the reactants must equal the total mass of the products in a chemical reaction, as dictated by the Law of Conservation of Mass.

When lead nitrate is heated strongly it breaks down to form simpler substances like lead monoxide,nitrogen dioxide and oxygen.In this decomposition reaction the colourless compound lead nitrate forms a yellow compound lead monoxide and brown fumes of nitrogen dioxide gas are evolved

• Ferrous sulphate is a chemical compound with the formula FeSO4.


• When in solid form, ferrous sulphate is commonly known as iron(II) sulfate.


• The color of solid ferrous sulphate is green.


• It is important to note that the color of ferrous sulphate can vary depending on its hydration state.


• When hydrated, ferrous sulphate can appear as light green or blue-green.


• However, in its anhydrous form, solid ferrous sulphate is typically green.

• Type of reaction: Double displacement


• Explanation:
  
  
  
  • When sodium sulphate (Na2SO4) reacts with barium chloride (BaCl2), a double displacement reaction occurs.
  
  
  • In this reaction, the positive ions of the two compounds switch places to form sodium chloride (NaCl) and barium sulphate (BaSO4).
  
  
  • The balanced chemical equation for the reaction is: Na2SO4 + BaCl2 → 2NaCl + BaSO4
  
  
  • Here, sodium and barium switch partners, resulting in the formation of two new compounds.
  
  
  • The products formed are insoluble in water, leading to the formation of a precipitate (barium sulphate) which can be easily separated from the solution.
  
  
  
  

• Reactivity Comparison: Iron is more reactive than copper. This can be observed in the reaction where iron displaces copper from copper sulfate solution to form iron sulfate and copper metal. This indicates that iron is more reactive than copper.


• Oxidation and Reduction: In this reaction, copper is being displaced by iron. This means that copper is being oxidized (losing electrons) and iron is being reduced (gaining electrons). This can be seen in the formation of FeSO₄ and Cu as products.

• Type of Reaction: Decomposition reaction


• Process: Endothermic process

• Decomposition Reaction: CaCO₃ decomposes into CaO and CO₂ when heated.


• Endothermic Process: This reaction requires energy input in the form of heat to break the bonds within CaCO₃ and form CaO and CO₂.

• Decomposition Reaction: In a decomposition reaction, a single compound breaks down into two or more simpler substances.


• Endothermic Process: Endothermic processes absorb heat from their surroundings to proceed, resulting in a decrease in temperature of the surroundings.

• Combination Reaction: In a combination reaction, two or more reactants combine to form a single product.


• Displacement Reaction: In a displacement reaction, one element displaces another in a compound.

Therefore, in this scenario, the reaction of heating CaCO₃ to produce CaO and CO₂ is a decomposition reaction and the process is an endothermic process.

• Boiling of water to give water vapour: This is a physical change as the water undergoes a phase change from liquid to gas without any change in its chemical composition.


• Melting of ice to give water: This is also a physical change as the ice undergoes a phase change from solid to liquid without any change in its chemical composition.


• Dissolution of salt in water: This is a physical change as the salt particles mix with water particles to form a homogeneous solution, but there is no change in the chemical composition of the salt.


• Combustion of Liquefied Petroleum Gas (LPG): This is a chemical change as the LPG undergoes a combustion reaction with oxygen to produce heat, light, carbon dioxide, and water vapor. Chemical bonds are broken and new ones are formed in this process, resulting in a change in the chemical composition of the LPG.

• KMnO₄ is an oxidising agent, it oxidises FeSO₄: This statement is incorrect because in this reaction, FeSO₄ is the reducing agent, not the oxidising agent.


• FeSO₄ acts as an oxidising agent and oxidises KMnO₄: This statement is also incorrect as FeSO₄ is a reducing agent in this reaction and not an oxidising agent.


• The colour disappears due to dilution; no reaction is involved: This statement is incorrect because the disappearance of the color is not due to dilution but due to a chemical reaction taking place.


• KMnO₄ is an unstable compound and decomposes in presence of FeSO₄ to a colourless compound: This is the correct explanation for the observation. In this reaction, FeSO₄ acts as a reducing agent and reduces KMnO₄ to form a colorless compound, resulting in the disappearance of the light purple color of the solution.

• Electrolysis of water: Electrolysis of water is a decomposition reaction in which water (H₂O) is split into its constituent elements, hydrogen (H₂) and oxygen (O₂), using electricity.


• Chemical equation: The balanced chemical equation for the electrolysis of water is 2H₂O(l) -> 2H₂(g) + O₂(g).


• Mole ratio: From the balanced chemical equation, it is clear that for every 2 moles of water decomposed, 2 moles of hydrogen gas and 1 mole of oxygen gas are produced.


• Ratio of hydrogen to oxygen: The mole ratio of hydrogen to oxygen gases liberated during the electrolysis of water is 2 : 1.

• Storage of fresh sample of an oil: When storing a fresh sample of oil, it is important to prevent oxidation and degradation of the oil.


• Role of gases: Certain gases can help in preserving the freshness of the oil by creating a protective atmosphere.

• Option A: Carbon dioxide or oxygen - Oxygen can lead to oxidation of the oil, so this is not an ideal choice for long-term storage.


• Option B: Nitrogen or oxygen - As mentioned before, oxygen can lead to oxidation, so nitrogen would be a better choice for storage.


• Option C: Carbon dioxide or helium - Carbon dioxide can react with the oil and alter its properties, so helium might be a better choice for storage.


• Option D: Helium or nitrogen - Both helium and nitrogen are inert gases that can create a protective atmosphere for the oil, preventing oxidation and degradation. This makes option D the best choice for long-term storage of a fresh sample of oil.

• Therefore, helium or nitrogen are the recommended gases for storage of a fresh sample of oil for a long time.

• Correct States: The given chemical equation represents the reaction between hydrogen gas (H₂) and oxygen gas (O₂) to form water (H₂O) in the liquid state.


• State Symbols: In the chemical equation, the state symbols are important to indicate the physical state of each substance involved in the reaction.


• Hydrogen Gas (H₂): Hydrogen gas is represented by (g) to indicate that it is in the gaseous state.


• Oxygen Gas (O₂): Oxygen gas is also represented by (g) to indicate that it is in the gaseous state.


• Water (H₂O): In the correct equation, water should be in the liquid state, represented by (l).


• Analysis: Examining each option, we find that option C: 2H₂(g) + O₂(g) → 2H₂O(l) has the correct states for the reactants and products.


• Conclusion: Therefore, option C is the correct choice where the abbreviations represent the correct states of the reactants and products involved at reaction temperature.

• Given reaction: 2Pb(NO₃)₂ → 2PbO + nA + O_2>


• Balancing the equation: In the reaction, there are 2 atoms of lead (Pb) on the left side and only 1 atom of lead on the right side. Therefore, to balance the equation, we need to have 2 atoms of lead on the right side as well. So, the balanced equation becomes: 2Pb(NO₃)₂ → 2PbO + nA + O₂


• Finding the value of n: To find the value of n, we need to look at the nitrate ions (NO₃). There are 4 nitrate ions on the left side (2 x NO₃) and only 2 nitrate ions on the right side (nA). Therefore, n must be equal to 4 in order to balance the equation.


• Final balanced equation: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

Therefore, the correct answer is option B: 4NO₂.

• Definition: Rust is a reddish-brown oxide that forms on iron or steel due to the reaction of iron and oxygen in the presence of moisture or water.


• Chemical Composition: The chemical formula for rust is Fe2O3, which represents iron oxide.


• Formation: Rust forms when iron or steel is exposed to oxygen and water, leading to the oxidation of the metal surface.


• Characteristics: Rust is a brittle, flaky substance that weakens the structural integrity of iron or steel objects over time.


• Prevention: To prevent rust formation, protective coatings such as paint or anti-corrosion treatments can be applied to metal surfaces.


• Effects: Rust can cause metal objects to deteriorate, leading to structural failure and reduced lifespan.


• Removal: Rust can be removed using mechanical methods such as sanding or chemical treatments like rust converters.

• When sulphuric acid (H₂SO₄) is poured over zinc (Zn), a chemical reaction takes place.

• The reaction results in the formation of hydrogen gas (H₂).

• The chemical equation for this reaction is:

Zn + H₂SO₄ → ZnSO₄ + H₂

• When zinc reacts with sulphuric acid, zinc sulfate and hydrogen gas are produced.


• Hydrogen gas is released as bubbles during the reaction.


• This gas can be tested by placing a burning splint near the reaction mixture, resulting in a 'pop' sound due to the combustion of hydrogen gas.

• Therefore, when sulphuric acid is poured over zinc, hydrogen gas is formed as a product of the reaction.