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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 10CBSE

How many chromosomes are found in human ovum? a) 46 b) 64 c) 23 d) 32

In human beings, chromosomes are very important because they carry genetic information such as traits, features, and characteristics. Every normal body cell in humans contains 46 chromosomes, arranged in 23 pairs. However, not all cells have the same number of chromosomes.The human ovum (egg cell) is a special type of cell called a gamete or reproductive cell. Unlike normal body cells, the ovum contains only 23 chromosomes, not 46. This is because the ovum is haploid, meaning it has only one set of chromosomes. This difference is very important for reproduction. During fertilization, the ovum (female gamete) combines with the sperm (male gamete). The sperm also carries 23 chromosomes. When both fuse, they form a zygote with a total of 46 chromosomes, restoring the normal number. This process ensures that the number of chromosomes remains constant from one generation to the next. If the ovum had 46 chromosomes, the number would double after fertilization, which would cause serious problems.Another important point is that the ovum always carries an X chromosome as its sex chromosome. On the other hand, the sperm can carry either an X or a Y chromosome. This means that the sperm determines the gender of the baby.The ovum is formed through a process called meiosis, which reduces the number of chromosomes from 46 to 23. This reduction is necessary to maintain balance in the chromosome number during reproduction.Key Points to Remember:Human body cells: 46 chromosomes (diploid)Human ovum: 23 chromosomes (haploid)Ovum always carries: X chromosomeFertilization: 23 (ovum) + 23 (sperm) = 46 chromosomes (zygote)Conclusion:The correct answer to the question “Chromosomes are found in human ovum” is 23 chromosomes. The ovum is a haploid cell, and this feature plays a very important role in maintaining genetic balance in humans.

ScienceClass 10CBSE

Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of – 50 cm. What is the nature of the lens and its power used by each of them?

Soln: Degree of convergence and divergence provided by a lens is called power of the lens. Unit of power of lens is Diopter D. focal length of lens used by first student is in positive hence it is a convex lens. The lens of second student is a concave lens. p== 1= 1 =2 𝑓 0.5 Power of lens (first student) =+2 Power of lens (second student) = ).2

ScienceClass 10CBSE

Size of image of an object by a mirror having a focal length of 20 cm is observed to be reduced to 1/3rd of its size. At what distance the object has been placed from the mirror? What is the nature of the image and the mirror?

Soln: m = 1 3 Using 1 + 1= 1 𝑣 𝑢 𝑓 Calculate u;u = – 80 cm. Image is real and inverted. Mirror is concave.

ScienceClass 10CBSE

The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between lens and image is 80 cm, at what distance should the candle be placed from the lens? What is the nature of the image at a distance of 80 cm and the lens?

Soln: As the image is obtained on the screen , it is real . so, Magnification , m = –3 , v = 80 cm u = ? As m = v/u so, –3 = 80/u, u = –80/3 cm . From 1/f = 1/v - 1/u =1/80 + 3/80 = 4/80 = 1/20 1/f = 1/20cm so, f = 20 cm . The lens is convex and image formed at 80 cm from the lens is real and inverted.

ScienceClass 10CBSE

How are power and focal length of a lens related? You are provided with two lenses of focal length 20 cm and 40 cm respectively. Which lens will you use to obtain more convergent light?

Soln: Power of lens is inversely proportional to the focal length of the lens. Lens with focal length 20 has more power than lens with focal length 40 cm. Lens with higher power should be used to obtain more convergent light.

ScienceClass 10CBSE

Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of 15 cm from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?

Soln: To obtain clear image of the building Sudha has to move the screen towards the elns. Focal length will be approximately 15 cm. The rays of light coming from distant object such as a tree (or a distant building or electricity pole) can be considered to be parallel to each other. When parallel rays of light are incident on a convex lens, the rays, after refraction, converge at focus on the other side of the lens.

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