CBSE Class 10 Science Chapter 3 Metals and Non-metals - Exercise Question Answer

 CBSE Class 10 Science Chapter 3 Metals and Non-metals - Exercise Question Answer

Q1.	Which of the following pairs will give displacement reactions? (a) NaCl solution and copper metal (b) MgCl2 solution and aluminium metal (c) FeSO4 solution and silver metal (d) AgNO3 solution and copper metal.
Ans.	Displacement reactions occur when a more reactive metal displaces a less reactive metal from its salt solution. The reactivity series for the metals mentioned in the options, from most reactive to least reactive: Aluminium (Al) Zinc (Zn) Iron (Fe) Copper (Cu) Silver (Ag) (a) Copper is less reactive than sodium (Na). Therefore, No displacement reaction will occur. (b) Aluminium is more reactive than magnesium (Mg). Therefore, No displacement reaction will occur. (c) Silver (Ag) is less reactive than iron (Fe). Therefore, No displacement reaction will occur. (d) Copper is more reactive than silver (Ag). Therefore, A displacement reaction will occur. Cu(s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag (s) So, Option (d) is correct.
Q2,	Which of the following methods is suitable for preventing an iron frying pan from rusting? (a) Applying grease (b) Applying paint (c) Applying a coating of zinc (d) All of the above.
Ans.	Option (c) Applying a coating of zinc is correct. Applying grease and paint can effectively prevent rusting in some cases, but they are not practical methods for preventing rust on a frying pan. Therefore, the most suitable and practical approach to prevent rust on an iron frying pan is to apply a zinc coating. This method is known as galvanizing.
Q3.	An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be (a) calcium (b) carbon (c) silicon (d) iron
Ans.	Option (a) is correct. Calcium reacts with oxygen to produce calcium oxide, which is soluble in water, forming calcium hydroxide. Carbon reacts with oxygen to create carbon oxides, which is insoluble in water. Silicon reacts with oxygen to form silicon dioxide, which is insoluble in water. Iron reacts with oxygen to yield iron oxides, which is insoluble in water.
Q4.	Food cans are coated with tin and not with zinc because (a) zinc is costlier than tin. (b) zinc has a higher melting point than tin. (c) zinc is more reactive than tin. (d) zinc is less reactive than tin.
Ans.	Option (c) is correct. Food cans are coated with tin rather than zinc because zinc is more reactive or electropositive than tin.
Q5.	You are given a hammer, a battery, a bulb, wires and a switch. (a) How could you use them to distinguish between samples of metals and non-metals? (b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
Ans.	(a) Metals exhibit malleability, which means they can be easily shaped into sheets by hammering. In other side, non-metals are brittle and tend to break when use force. Metals are conductors of electricity and when connected to a battery, wire and bulb, they can complete the electrical circuit and light up the bulb. In other side, non-metals are poor conductors of electricity and cannot light up the bulb. (b) These experiments show effective demonstrations of properties of metals and non-metals like their malleability and electrical conductivity.
Q6.	What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans.	Amphoteric oxides are oxides that can show both acidic and basic behavior when they react with other substances and forms salt and water. Example: PbO and Al2O3 With a strong acid (HCl): Al2O3 + 6HCl → 2AlCl3 + 3H2O With a strong base (NaOH): Al2O3 + 2NaOH → 2NaAlO2 + H2O
Q7.	Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Ans.	Zinc (Zn) and Magnesium (Mg) metals can displace hydrogen from dilute acids. Gold (Au) and Silver (Ag) metals can’t displace hydrogen from dilute acids.
Q8.	In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Ans.	In the electrolytic refining of metal M: The anode is made of impure metal M which we want to refine. The cathode is made of pure metal M (usually the same metal, but pure). The electrolyte contains metal ions of M which is a suitable salt solution of metal.
Q9.	Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below. (a) What will be the action of gas on (i) dry litmus paper? (ii) moist litmus paper? (b) Write a balanced chemical equation for the reaction taking place.
Ans.	(a) The gas collected by Pratyush in the test tube is sulfur dioxide (SO2), which is an acidic gas. Sulfur + Oxygen + Heat → Sulfur Dioxide (i) Dry litmus paper remains unchanged because dry litmus paper is not sensitive to acidic or basic gases. (ii) Moist litmus paper turns blue litmus paper into red. This indicates that the gas is acidic. (b) Balanced equation: S(s) + O2(g) → SO2(g) SO2(g) + H2O →H2SO3
Q10.	State two ways to prevent the rusting of iron.
Ans.	Iron can be protected from rusting by applying rust-resistant paint to the iron's surface. Another method is to use oil or grease, which acts as a barrier, preventing the iron from coming into contact with moist air.
Q11.	What types of oxides are formed when non-metals combine with oxygen?
Ans.	When non-metals combine with oxygen, they form acidic oxides, which are known as non-metallic or covalent oxides. These oxides are acidic and can produce acidic solutions when dissolved in water. Some non-metals form neutrals. Example: sulfur dioxide (SO2), carbon dioxide (CO2), nitrogen dioxide (NO2), N2O5 or N2O3 is an acidic oxide; CO is a neutral oxide.
Q12.	Give reasons (a) Platinum, gold and silver are used to make jewellery. (b) Sodium, potassium and lithium are stored under oil. (c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. (d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Ans.	(a) Platinum, gold, and silver are chosen for making jewelry due to their minimal reactivity. These metals remain unaffected by air, water, and most chemicals. They possess a high degree of luster (shiny), are malleable and ductile, and have exceptional resistance to corrosion. (b) Sodium, potassium, and lithium are stored under oil to prevent them from reacting with moisture and oxygen in the air. They are react with water and release hydrogen gas and heat, this may cause of fire. (c) Aluminum is a highly reactive metal, but it is used to make utensils for cooking because it forms a thin, protective oxide layer on its surface when exposed to air. This oxide layer prevents further corrosion and makes aluminum safe for cooking. (d) Carbonate and sulfide ores are usually converted into oxides during the process of extraction because oxides are easier to reduce and extract the metal from. By converting ores into oxides, the subsequent reduction and purification of the metal become more efficient.
Q13.	You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Ans.	Lemon or tamarind juice effectively clean tarnished copper vessels because their citric acid content reacts with the tarnish (copper oxide or copper carbonate), dissolving it and restoring the vessel's shine. CuO + C6H8O7 (citric acid) → Cu²⁺ + C6H6O7 (citrate ion) + H2O For copper oxide (CuO): CuO + 2H+ → Cu2+ + H2O For copper carbonate (CuCO3): CuCO3 + 2H+ → Cu2+ + H2O + CO2
Q14.	Differentiate between metal and non-metal on the basis of their chemical properties.
Ans.	Property Metals Non-Metals Reaction with Oxygen Form metal oxides (Ex. rust) Form non-metallic oxides (Ex.  sulfur dioxide) Reaction with Water React with water to form metal oxides and hydrogen gas (Ex. sodium) Generally do not react with water, except for a few exceptions Reaction with Acids React with acids to form salts and release hydrogen gas (Ex. zinc with HCl) Do not react with acids Formation of Ions Tend to lose electrons to form positively charged ions (cations) (Ex. Na⁺) Tend to gain electrons to form negatively charged ions (anions) (Ex. Cl⁻) Electrical Conductivity Good conductors of electricity due to free electrons (Ex. copper) Poor conductors of electricity due to a lack of free electrons (Ex. sulfur) Bonding Typically form metallic bonds with delocalized electrons Typically form covalent bonds with shared electrons States at Room Temperature Solid (except mercury) Gases, liquids or brittle solids Luster and Malleability Lustrous and malleable (can be hammered into thin sheets) Often not lustrous and not malleable
Q15.	A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Ans.	The goldsmith used a solution known as Aqua regia, which is Latin for 'royal water.' Aqua regia is created by mixing concentrated hydrochloric acid and concentrated nitric acid in a 3:1 ratio. This potent mixture has the ability to dissolve noble metals like gold and platinum. When applied to dull gold ornaments, it removes the upper layer, resulting in their weight loss.
Q16.	Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Ans.	Copper is preferred over steel for making hot water tanks due to its corrosion resistance, heat conductivity, lightweight nature, malleability, non-toxicity, longevity, and energy efficiency and it does not react with water or steam. These all specialty make it an excellent choice for hot water storage and heating applications.