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ScienceClass 10CBSE

Why are non-metals generally poor conductors of electricity, while metals are good conductors?

Metals have a 'sea' of delocalized electrons that are free to move throughout the metallic lattice. These free electrons are responsible for conducting electricity. Non-metals, on the other hand, typically hold their electrons tightly in covalent bonds or have a complete outer shell, meaning they do not have free electrons to carry an electric current, making them poor conductors. Graphite is an exception among non-metals due to its unique layered structure with delocalized electrons.

ScienceClass 10CBSE

Explain the concept of thermite reaction. Where is it primarily used?

The thermite reaction is a highly exothermic redox reaction between a metal oxide and a more reactive metal (usually aluminium) powder. In this reaction, aluminium reduces the metal oxide to its molten metal state, generating a large amount of heat. A common example is the reaction between iron(III) oxide and aluminium: Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + Heat. It is primarily used for welding railway tracks and cracked machine parts due to the high temperature produced and the molten iron formed.

ScienceClass 10CBSE

What are amphoteric oxides? Give an example and write balanced chemical equations for its reaction with both an acid and a base.

Amphoteric oxides are metal oxides that react with both acids and bases to produce salt and water. An example is aluminium oxide (Al2O3). Reaction with acid: Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l) Reaction with base: Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) + H2O(l) (or 2NaOH(aq) + Al2O3(s) + 3H2O(l) → 2Na[Al(OH)4](aq) depending on the form of sodium aluminate)

ScienceClass 10CBSE

Explain why sodium metal is stored under kerosene oil.

Sodium is a highly reactive metal. It reacts vigorously with oxygen and moisture present in the air, sometimes even catching fire. To prevent this reaction and ensure its safe storage, sodium metal is kept immersed in kerosene oil, which is unreactive with sodium and prevents its contact with air and water.

ScienceClass 10CBSE

Why do metals generally form positive ions (cations), while non-metals generally form negative ions (anions)?

Metals typically have 1, 2, or 3 electrons in their outermost shell. They tend to lose these valence electrons to achieve a stable noble gas configuration, forming positively charged ions (cations). Non-metals, on the other hand, usually have 4 to 7 electrons in their outermost shell. They tend to gain electrons to complete their octet and achieve a stable noble gas configuration, forming negatively charged ions (anions).

ScienceClass 10CBSE

Differentiate between malleability and ductility, providing an example of a metal that exhibits both properties prominently.

Malleability is the property of a material to be hammered or pressed into thin sheets without breaking. Ductility is the property of a material to be drawn into thin wires without breaking. Gold is an excellent example of a metal that exhibits both malleability and ductility prominently, allowing it to be beaten into extremely thin foils and drawn into fine wires.

ScienceClass 10CBSE

What is corrosion? Explain the conditions necessary for the rusting of iron and suggest two methods to prevent it.

Corrosion is the gradual deterioration of a material, usually a metal, by chemical reaction with its environment. Rusting is a specific type of corrosion that affects iron and its alloys. The conditions necessary for rusting of iron are the presence of both oxygen (from air) and water (moisture). Two methods to prevent rusting include painting (which creates a barrier between the iron and the environment) and galvanization (coating iron with a layer of zinc, which acts as a sacrificial metal).

ScienceClass 10CBSE

Describe the process of extracting metals from their ores, specifically focusing on the steps involved for moderately reactive metals.

Moderately reactive metals like zinc, iron, and lead are usually found as sulphides or carbonates in their ores. The extraction process typically involves: 1. Concentration of the ore. 2. Conversion of sulphide ores to oxides by roasting (heating in air). 3. Conversion of carbonate ores to oxides by calcination (heating in limited air). 4. Reduction of the metal oxides to the metal using a reducing agent like carbon. For example, ZnO + C → Zn + CO.

ScienceClass 10CBSE

What are ionic compounds? Explain their formation with a suitable example.

Ionic compounds are chemical compounds formed by the electrostatic attraction between oppositely charged ions. They are typically formed between a metal and a non-metal, where the metal atom loses electrons to form a positive ion (cation) and the non-metal atom gains electrons to form a negative ion (anion). For example, in the formation of sodium chloride (NaCl), sodium (Na) loses one electron to become Na+, and chlorine (Cl) gains one electron to become Cl-. The electrostatic attraction between Na+ and Cl- forms the ionic bond.

ScienceClass 10CBSE

Describe the reactivity series of metals. Why is it important in understanding the displacement reactions?

The reactivity series is a list of metals arranged in the order of their decreasing reactivity. Metals at the top of the series are more reactive than those at the bottom. It is important because it helps predict whether a metal will displace another metal from its salt solution. A more reactive metal can displace a less reactive metal from its compound.

ScienceClass 10CBSE

Explain the key physical differences between metals and non-metals, providing at least three distinct properties for each.

Metals are generally lustrous, malleable, ductile, good conductors of heat and electricity, and solid at room temperature (except mercury). Non-metals are typically dull, brittle, non-ductile, poor conductors of heat and electricity (except graphite), and can exist as solids, liquids, or gases at room temperature.

ScienceClass 10CBSE

List three uses of non-metals in everyday life and explain their significance.

Oxygen: Essential for respiration in living organisms and combustion processes. Without oxygen, life as we know it would not exist, and many industrial processes like burning fuels would be impossible.Nitrogen: Used in fertilizers (e.g., urea, ammonia) for plant growth, and as an inert atmosphere in packaging food items to prevent spoilage. It is crucial for agriculture and food preservation.Chlorine: Used as a disinfectant for water purification (killing harmful bacteria) and in the production of PVC and bleaching agents. It plays a vital role in public health and various chemical industries.

ScienceClass 10CBSE

Why do ionic compounds have high melting and boiling points?

Ionic compounds are formed by strong electrostatic forces of attraction between oppositely charged ions. These forces are very strong and extend throughout the entire crystal lattice. A significant amount of energy is required to overcome these strong inter-ionic forces and break down the crystal structure, allowing the ions to move freely (melt) or separate completely (boil). Therefore, ionic compounds typically have high melting and boiling points.

ScienceClass 10CBSE

Describe the method of froth flotation used for concentrating sulphide ores.

Froth flotation is a metallurgical process used for concentrating sulphide ores. The finely powdered ore is mixed with water, a frothing agent (like pine oil), and a collector (like potassium ethyl xanthate). Air is then blown into the mixture through a rotating paddle. The frothing agent creates a stable froth, and the collector selectively adheres to the sulphide ore particles, making them water-repellent (hydrophobic) and oil-attracting.These oil-coated ore particles become lighter and rise with the froth to the surface, which is then skimmed off. The gangue (impurities) particles, being hydrophilic, settle down at the bottom.

ScienceClass 10CBSE

Explain the difference between roasting and calcination in the context of metal extraction. When is each process used?

Both roasting and calcination are processes used to convert metal ores into their oxides before reduction.Roasting: This process involves heating a sulphide ore strongly in the presence of excess air. The sulphide ore is converted into its metal oxide and sulphur dioxide gas is released. It is used for sulphide ores (e.g., 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)).Calcination: This process involves heating a carbonate ore or hydrated oxide ore strongly in a limited supply of air or in the absence of air. The carbonate ore decomposes to form its metal oxide and carbon dioxide gas. It is used for carbonate ores (e.g., ZnCO3(s) → ZnO(s) + CO2(g)) and hydrated oxides.

ScienceClass 10CBSE

Describe the electrolytic refining of copper. Include a labelled diagram.

Electrolytic refining is the most widely used method for refining impure metals like copper. In this process, the impure metal is made the anode, and a thin strip of pure metal is made the cathode. An aqueous solution of a salt of the metal (e.g., acidified copper sulphate for copper) is used as the electrolyte. When an electric current is passed:At the anode (impure copper), the impure metal oxidizes, and metal ions (e.g., Cu2+) dissolve into the electrolyte. More reactive impurities also dissolve, while less reactive impurities settle down as 'anode mud'.At the cathode (pure copper), the metal ions from the electrolyte gain electrons and deposit as pure metal.The overall effect is the transfer of pure metal from the anode to the cathode.

ScienceClass 10CBSE

What is galvanization? How does it protect iron from rusting?

Galvanization is the process of coating iron or steel with a thin layer of zinc. It protects iron from rusting in two main ways: Barrier Protection: The zinc layer acts as a physical barrier, preventing the iron from coming into contact with oxygen and moisture. Sacrificial Protection: Zinc is more reactive than iron. If the zinc coating is scratched, the zinc will corrode preferentially (sacrifice itself) to protect the underlying iron from rusting, as it will lose electrons more readily than iron.

ScienceClass 10CBSE

Give two chemical properties that distinguish metals from non-metals, and provide an example for each.

1. Reaction with Oxygen: Metals generally react with oxygen to form basic oxides (e.g., 2Mg(s) + O2(g) → 2MgO(s), where MgO is basic). Non-metals react with oxygen to form acidic or neutral oxides (e.g., C(s) + O2(g) → CO2(g), where CO2 is acidic).2. Reaction with Acids: Metals above hydrogen in the reactivity series react with dilute acids to produce hydrogen gas (e.g., Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)). Non-metals generally do not react with dilute acids to produce hydrogen gas.

ScienceClass 6CBSE

Water Conservation

Water is a limited resource, so it must be used wisely. We can conserve water by: Avoiding wastage Repairing leaking taps Using water carefully in daily activities Not polluting rivers and ponds Practicing rainwater harvesting Planting trees and protecting forests

ScienceClass 6CBSE

Uses of Water

Water is used in many ways in our daily life: Drinking, cooking, bathing, and cleaning Agriculture for growing crops Industries for manufacturing processes Generating electricity (hydropower)

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