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CBSE Class 12 Board Exam 2020 : Chemistry (Series 1) |
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Zinc
Tin
Zinc provides better protection for iron objects because it is more reactive than iron and forms a protective layer of zinc oxide when exposed to air. This galvanization process sacrificially corrodes to protect the underlying iron. Tin, while also used for coating, is less effective as it is less reactive than iron.
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CBSE Class 12 Board Exam 2020 : Chemistry (Series 1) |
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CH2=CHCl
Branched alkyl groups
The monomer of PVC (polyvinyl chloride) is vinyl chloride, which has the structure CH2=CHCl.
The structural unit that makes detergents non-biodegradable is typically branched alkyl groups. These branched structures are more resistant to breakdown by microorganisms, leading to environmental persistence.
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CBSE Class 12 Board Exam 2020 : Chemistry (Series 1) |
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Zinc
Tin
Zinc provides better protection for iron objects because it is more reactive than iron and forms a protective layer of zinc oxide when exposed to air. This galvanization process sacrificially corrodes to protect the underlying iron. Tin, while also used for coating, is less effective as it is less reactive than iron.
ghjhjhjlkj
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CBSE Class 12 Board Exam 2020 : Chemistry (Series 1) |
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No
If the activation energy (Eact) of a reaction is zero, the rate constant will not depend on temperature (T). This is because the Arrhenius equation, which relates rate constant to temperature, becomes independent of T when Eact = 0. In this case, the rate constant would remain constant regardless of temperature changes.
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CBSE Class 12 Board Exam 2020 : Chemistry (Series 1) |
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A
The liquid with the lower boiling point will have a higher vapor pressure at a given temperature. Liquid A has a boiling point of 140°C, which is lower than liquid B's boiling point of 180°C. Therefore, at 90°C, liquid A will have a higher vapor pressure.
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CBSE Class 12 Board Exam 2020 : Chemistry (Series 1) |
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When anisole is treated with various reagents, it undergoes different reactions based on the nature of the reagent. Here are the structures of the products formed:
a) HI (Hydroiodic acid):
The product is phenol and methyl iodide (CH3I). HI cleaves the ether linkage.
C6H5-O-CH3 + HI → C6H5-OH + CH3I
b) Br2/FeBr3 (Bromination):
The product is 4-bromoanisole. Anisole undergoes electrophilic aromatic substitution, with the methoxy group directing to the para position.
C6H5-O-CH3 + Br2 → 4-Br-C6H4-O-CH3 + HBr
c) CH3COCl/AlCl3 (Friedel-Crafts acylation):
The product is 4-methoxyacetophenone. The reaction occurs at the para position due to the directing effect of the methoxy group.
C6H5-O-CH3 + CH3COCl → 4-CH3CO-C6H4-O-CH3 + HCl
d) CH3Cl/AlCl3 (Friedel-Crafts alkylation):
The product is 4-methylanisole. Again, the methoxy group directs the substitution to the para position.
C6H5-O-CH3 + CH3Cl → 4-CH3-C6H4-O-CH3 + HCl
These reactions demonstrate the reactivity of anisole and the directing effect of the methoxy group in electrophilic aromatic substitutions.
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Pune University - Msc - I (Sem - II) : Metamorphic Petrology, April 2010 |
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Metamorphism is the process of changing a rock's mineralogy, texture, or chemical composition due to exposure to heat, pressure, or chemically active fluids, without melting the rock completely. This process occurs in the solid state and results in the formation of metamorphic rocks.
Common minerals found in metamorphic rocks include:
1. Quartz
2. Feldspars
3. Micas (biotite, muscovite)
4. Amphiboles (hornblende)
5. Garnet
6. Staurolite
7. Kyanite
8. Sillimanite
9. Andalusite
10. Chlorite
Genesis and occurrence:
These minerals form through various metamorphic reactions, often involving the breakdown of pre-existing minerals and the growth of new ones. Their occurrence depends on factors such as:
1. Original rock composition
2. Temperature and pressure conditions
3. Availability of fluids
4. Duration of metamorphism
For example, garnet typically forms in medium to high-grade metamorphic rocks, while chlorite is more common in low-grade metamorphism. Quartz and feldspars are often present in the original rock and may persist through metamorphism. Micas form through the breakdown of clay minerals or feldspars. The aluminum silicates (kyanite, sillimanite, and andalusite) form under specific pressure-temperature conditions and are useful indicators of metamorphic grade.
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ICSE Class X Prelims 2025 : Chemistry 2nd prelims (Smt. Sulochanadevi Singhania School, Thane) |
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(a) 2,2,3-Trimethylbut-3-ene
The compound shown in the image is named according to IUPAC nomenclature as follows:
- The longest carbon chain contains 4 carbon atoms, so the root name is "but".
- There is a double bond, so we add the suffix "-ene".
- The double bond is at the 3rd carbon, so we insert "3-" before "ene".
- There are three methyl groups: two at the 2nd carbon and one at the 3rd carbon.
- We list the substituents in alphabetical order, so "2,2,3-trimethyl".
(b) 2-Methylpropanal
For the second compound (CH3-CH(CH3)-CHO):
- The longest carbon chain containing the aldehyde group has 3 carbons, so the root name is "propan".
- The aldehyde group (-CHO) is indicated by the suffix "-al".
- There is a methyl group (-CH3) attached to the 2nd carbon.
- Combining these gives us "2-methylpropanal".
garviv
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ICSE Class X Prelims 2025 : Chemistry 2nd prelims (Smt. Sulochanadevi Singhania School, Thane) |
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(a) Homologous series
(b) Lone pair of electrons
(c) Ores
(d) Electrolysis
(e) Electron affinity
Reasoning:
(a) A homologous series is a group of organic compounds with similar chemical properties and structures, differing by a CH2 group between successive members.
(b) Lone pairs are electrons in an atom that are not involved in bonding and remain localized on the atom.
(c) Ores are naturally occurring rock formations containing minerals from which metals can be extracted economically.
(d) Electrolysis is a process that uses electricity to separate ions in an ionic compound, often used in purification or extraction of elements.
(e) Electron affinity is the energy released when a gaseous atom accepts an electron to form a negative ion (anion). It's an important concept in understanding chemical bonding and reactivity.
garviv
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ICSE Class X Prelims 2025 : Chemistry 2nd prelims (Smt. Sulochanadevi Singhania School, Thane) |
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(a) First, let's calculate the molar masses:
CaCO3: 40 + 12 + (16 × 3) = 100 g/mol
CaCl2: 40 + (35.5 × 2) = 111 g/mol
From the equation, 1 mole of CaCO3 produces 1 mole of CaCl2.
10g of CaCO3 = 10/100 = 0.1 mole
0.1 mole of CaCl2 will be produced
Mass of CaCl2 = 0.1 × 111 = 11.1g
For CO2:
0.1 mole of CO2 will be produced
Volume at STP = 0.1 × 22.4 L = 2.24 L
(b) According to Avogadro's law, equal volumes of gases under the same conditions of temperature and pressure contain an equal number of molecules.
If 150 cc of gas A contains X molecules,
then 150 cc of gas B will also contain X molecules.
For 450 cc of gas B:
450/150 = 3
So, 450 cc of gas B will contain 3X molecules.
garviv
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ICSE Class X Prelims 2025 : Chemistry 2nd prelims (Smt. Sulochanadevi Singhania School, Thane) |
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(a) low
Reasoning: Acetic acid is a weak acid, while dilute sulphuric acid is a strong acid. Weak acids dissociate less in water, producing fewer H+ ions compared to strong acids. Therefore, acetic acid has a lower concentration of H+ ions, resulting in a higher pH than dilute sulphuric acid.
(b) only H2
Reasoning:
- Solution X with pH 1 is strongly acidic. When zinc reacts with an acid, it produces hydrogen gas: Zn + 2H+ → Zn2+ + H2
- Solution Y with pH 14 is strongly basic (alkaline). Zinc can react with strong bases in the presence of water to produce hydrogen gas: Zn + 2OH- + 2H2O → Zn(OH)4^2- + H2
In both cases, only hydrogen gas (H2) is evolved. O2 and Cl2 are not produced in these reactions.
garviv
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ICSE Class X Prelims 2025 : Chemistry 2nd prelims (Smt. Sulochanadevi Singhania School, Thane) |
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(a) When methyl orange is added to a mixture of ammonium hydroxide and dilute HCl, the solution will turn yellow. This is because the mixture becomes slightly basic due to the presence of excess ammonium hydroxide, and methyl orange is yellow in basic solutions.
(b) When sodium hydroxide is added to lead nitrate solution:
- In small amount: A white precipitate of lead hydroxide forms.
- In excess: The white precipitate dissolves, forming a clear solution of sodium plumbate.
(c) When ammonium nitrate is strongly heated, it decomposes, producing nitrous oxide gas and water vapor. The observation would be the formation of bubbles and possibly a slight mist in the test tube.
(d) When neutral FeCl3 is added to acetic acid solution, the color of the solution changes from pale yellow to reddish-brown due to the formation of iron(III) acetate complex.
(e) When copper sulphide reacts with dilute hydrochloric acid, hydrogen sulphide gas is evolved, which can be recognized by its characteristic rotten egg smell. The solution may also turn slightly greenish due to the formation of copper(II) chloride.
garviv
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ICSE Class X Prelims 2025 : Chemistry 2nd prelims (Smt. Sulochanadevi Singhania School, Thane) |
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The compound 'Q' formed when magnesium ribbon reacts with dilute HCl is magnesium chloride (MgCl2). The electron dot diagram for MgCl2 is:
Mg : :Cl :
·
: Cl :
In this diagram, magnesium (Mg) loses two electrons, which are gained by two chlorine (Cl) atoms. The dots represent the outer shell electrons, with each chlorine having 8 electrons (octet) and magnesium having none in its outer shell after forming the ionic bond.
garviv
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ICSE Class X Prelims 2025 : Economic Applications (Vivekananda Mission School (VMS), Joka, Kolkata) |
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d) Both (b) and (c)
Reasoning: In the long run, under perfect competition and monopolistic competition, firms earn only normal profits. This is because:
1. Perfect competition: In this market structure, there are many small firms selling identical products. Free entry and exit of firms ensures that any economic profits are competed away in the long run, leaving firms with only normal profits.
2. Monopolistic competition: This market form has many firms selling differentiated products. While firms may earn economic profits in the short run, the long-run equilibrium results in firms earning only normal profits due to free entry and exit.
Normal profit is the minimum level of profit required to keep a firm in business. It's considered a cost of production rather than an economic profit. Both perfect competition and monopolistic competition converge to this state in the long run, making option (d) the correct answer.
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ICSE Class X Prelims 2025 : Economic Applications (Vivekananda Mission School (VMS), Joka, Kolkata) |
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b) False
Reasoning: While traders do often use current accounts, it's not accurate to say that current accounts are mostly used by traders. Current accounts are widely used by individuals, businesses, and organizations of various types. They are designed for frequent transactions and daily financial operations, making them suitable for a broad range of users, including:
1. Individual consumers for everyday banking needs
2. Small and large businesses for managing cash flow
3. Non-profit organizations
4. Government entities
5. Professionals and service providers
Traders are just one subset of the diverse group of users who benefit from current accounts. Therefore, the statement that current accounts are mostly used by traders is false, as it oversimplifies and misrepresents the broad user base of these accounts.
vaishalisawant05
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