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The correct answer is Pressure.

Key Points

• The rate of a chemical reaction generally depends on several factors including concentration, temperature, and the presence of a catalyst.
• Pressure can influence the rate of reaction in cases where gases are involved, but it is not a general factor for all reactions.
• In reactions involving only solids or liquids, pressure typically has little to no effect on the rate of reaction.
• Key factors such as concentration, temperature, and catalysts directly affect the speed at which reactants are converted to products.

Additional Information

• Concentration
• The rate of reaction generally increases with the concentration of reactants because there are more particles available to collide and react.
• According to the collision theory, the frequency of effective collisions increases with concentration.
• Temperature
• Raising the temperature typically increases the rate of reaction as particles move faster and collide more energetically.
• Higher temperatures provide the energy needed to overcome activation energy barriers.
• Catalyst
• Catalysts speed up reactions without being consumed by lowering the activation energy required for the reaction to proceed.
• Enzymes are biological catalysts that play crucial roles in speeding up biochemical reactions.
• Activation Energy
• Activation energy is the minimum energy that reacting particles need to collide successfully and start a reaction.
• Lowering the activation energy increases the rate of reaction.

The correct answer is John Newlands.

Key Points

• John Newlands was an English chemist who first proposed the law of octaves in 1864.
• The law of octaves states that elements, when arranged by increasing atomic mass, exhibit similar properties at every eighth element.
• Newlands’ law was an early attempt to classify the elements in a systematic way before the development of the modern periodic table.
• His work was initially criticized, but it paved the way for the later development of the periodic table by Dmitri Mendeleev.

Additional Information

• Johann Dobereiner
• German chemist known for his work on the classification of elements.
• Introduced the concept of triads, groups of three elements with similar properties, in 1829.
• Triads were an early attempt to show a relationship between atomic weights and properties of elements.
• Dmitri Mendeleev
• Russian chemist who created the first widely accepted periodic table in 1869.
• Arranged elements by increasing atomic weight and grouped elements with similar properties.
• Predicted the existence and properties of undiscovered elements, which were later found.
• Henry Moseley
• British physicist who established the concept of atomic number in 1913.
• Showed that the periodic table should be arranged by atomic number, not atomic weight.
• His work led to the modern definition of the periodic table.

The correct answer is -1/2Δ[HI]/Δt.

Key Points

• The rate of reaction for the equation 2HI → I₂ + H₂ is expressed as the change in concentration of HI over time.
• Since 2 moles of HI decompose to form 1 mole each of I₂ and H₂, the rate of decrease of HI is twice the rate of formation of products.
• The negative sign indicates that the concentration of HI is decreasing over time.
• The factor of 1/2 accounts for the stoichiometric coefficient of HI in the balanced chemical equation, ensuring the correct rate expression.

Additional Information

• Rate of Reaction
• It is defined as the change in concentration of reactants or products per unit time.
• The rate can be expressed as the rate of disappearance of reactants or the rate of appearance of products.
• Stoichiometry
• It refers to the quantitative relationships between reactants and products in a balanced chemical equation.
• Stoichiometric coefficients are used to determine the relative amounts of substances consumed and produced in a reaction.
• Reaction Order
• It indicates the power to which the concentration of a reactant is raised in the rate law.
• Determined experimentally, it helps in understanding the dependence of the rate on reactant concentrations.
• Rate Law
• It is an equation that relates the rate of a reaction to the concentration of reactants.
• For the reaction aA + bB → cC, the rate law is usually written as Rate = k[A]^m[B]^n, where k is the rate constant and m, n are the orders of the reaction with respect to A and B, respectively.

The correct answer is B only.

Key Points

• Rusting of iron is a chemical change as it involves the formation of a new substance, iron oxide, which is different from the original material.
• Chemical changes result in the production of one or more new substances with different properties from the original substances.
• During rusting, iron reacts with oxygen and moisture in the environment, leading to corrosion.
• This process is irreversible under normal conditions, further confirming it as a chemical change.

Additional Information

• Physical vs Chemical Change
• Physical changes affect the form of a chemical substance but not its chemical composition (e.g., melting ice).
• Chemical changes involve making or breaking of bonds between atoms, resulting in new substances (e.g., burning wood).
• Indicators of Chemical Changes
• Change in color, temperature, formation of a precipitate, and evolution of gas are common indicators.
• Production of light or sound can also indicate a chemical change.
• Examples of Chemical Changes
• Burning of paper, digestion of food, and baking a cake are classic examples.
• These processes produce new substances with different properties from the reactants.
• Importance of Understanding Chemical Changes
• Helps in various industries such as pharmaceuticals, agriculture, and manufacturing.
• Understanding these changes is crucial in environmental science to address issues like pollution and recycling.

The correct answer is 0.25

Concept:

Mole:

• The mole is a unit of measurement for the amount of substance.
• One mole of any substance contains exactly \(6.022 \times 10^{23}\) entities (this number is known as Avogadro's number \(N_A\).
• Formula to calculate moles: \(n = \frac{N}{N_A}\)

Calculation:

Given,

Number of molecules of\( CO_2 = N = 1.506 \times 10^{23}\)

Avogadro's number, \(N_A = 6.022 \times 10^{23} , \text{molecules/mol}\)

Number of moles of \(CO_2\),

⇒ \(n = \frac{N}{N_A}\)

⇒\( n = \frac{1.506 \times 10^{23}}{6.022 \times 10^{23}}\)

⇒ \(n \approx 0.25 \ moles\)

∴ The number of moles of \( CO_2 \) present is 0.25.

The correct answer is Did not change.

Key Points

• Sodium bicarbonate (NaHCO3) is a weak base and slightly alkaline in nature.
• pH paper is an indicator that changes color based on the pH of the substance it comes into contact with.
• Solid sodium bicarbonate typically has a pH around 8-9 when dissolved in water, but the solid form does not readily change the pH paper color.
• The color of the pH paper does not change significantly because the bicarbonate ions in the solid form are not free to react with the paper.

Additional Information

• pH Scale
• The pH scale ranges from 0 to 14, where 7 is neutral, below 7 is acidic, and above 7 is basic (alkaline).
• The pH paper is a tool used to measure the acidity or alkalinity of a solution.
• Sodium Bicarbonate
• Commonly known as baking soda, sodium bicarbonate is used in cooking, cleaning, and sometimes as a medicinal antacid.
• It is a chemical compound with the formula NaHCO3.
• Indicators
• Indicators are substances that change color in response to changes in pH.
• Common indicators include litmus paper, phenolphthalein, and methyl orange.
• Reactivity of Solids
• Solid compounds are generally less reactive with indicators compared to their aqueous solutions.
• This is because the ions in solids are not free to interact with the indicator.

The correct answer is Copper sulphate.

Key Points

• Copper sulphate (CuSO₄) is commonly used as the electrolyte in the electrolytic refining of copper.
• In this process, impure copper is used as the anode, and a pure copper sheet is used as the cathode.
• When an electric current is passed through the electrolyte solution, copper ions from the anode dissolve into the solution and are deposited on the cathode.
• Impurities present in the impure copper either remain in the solution or fall to the bottom as anode sludge.
• This process helps in obtaining high-purity copper from impure copper.

Additional Information

• Electrolytic Refining
• It is a process used to purify metals by electrolysis.
• This method is used for metals like copper, zinc, and aluminum.
• The process ensures the removal of impurities and produces high-purity metal.
• Copper Extraction
• Copper is extracted from its ores through processes like smelting and electrolysis.
• The extracted copper is further refined through electrolytic refining to achieve high purity.
• Applications of Copper
• Copper is widely used in electrical wiring due to its excellent electrical conductivity.
• It is also used in plumbing, roofing, and industrial machinery.
• Copper alloys, such as bronze and brass, have various applications in decorative arts and manufacturing.

The correct answer is Both H₃O⁺ and Cl⁻.

Key Points

• When hydrochloric acid (HCl) reacts with water (H₂O), it dissociates completely to form hydronium ions (H₃O⁺) and chloride ions (Cl⁻).
• This dissociation is a characteristic of strong acids like HCl, which ionize completely in aqueous solutions.
• The reaction can be written as: HCl + H₂O → H₃O⁺ + Cl⁻.
• Hydrochloric acid is a common laboratory reagent and is used in various industrial and chemical processes.

Additional Information

• Dissociation of Acids:
• Acids dissociate in water to release hydrogen ions (H⁺). In the case of strong acids like HCl, this process is complete.
• The hydrogen ions do not exist freely in solution but rather associate with water molecules to form hydronium ions (H₃O⁺).
• The general reaction for the dissociation of a strong acid HA in water is: HA + H₂O → H₃O⁺ + A⁻.
• Hydronium Ion (H₃O⁺):
• The hydronium ion is a positively charged ion formed when a hydrogen ion (H⁺) associates with a water molecule (H₂O).
• It is represented as H₃O⁺ and is the form in which protons are found in aqueous solution.
• Chloride Ion (Cl⁻):
• The chloride ion is a negatively charged ion formed when hydrochloric acid dissociates in water.
• It is represented as Cl⁻ and is a common anion found in various salts and solutions.
• Hydrochloric Acid (HCl):
• Hydrochloric acid is a strong acid that completely ionizes in water to form hydronium ions and chloride ions.
• It is widely used in the chemical industry for pH control, as a reagent in laboratories, and in the production of chlorides.

The correct answer is Zinc.

Key Points

• Zinc is the primary element used in the process of galvanization.
• Galvanization is a method used to protect iron and steel from rusting.
• During galvanization, a layer of zinc is applied to the surface of the metal.
• Zinc's natural resistance to corrosion helps prevent the underlying metal from rusting.

Additional Information

• Hot-dip Galvanization
• In this process, the metal is dipped into a bath of molten zinc.
• This method creates a thick, durable layer of zinc on the surface.
• Electro-galvanization
• This process uses an electric current to deposit a thin layer of zinc.
• It is often used for smaller items like screws and nails.
• Corrosion Protection
• Zinc acts as a sacrificial anode, meaning it will corrode first before the iron or steel does.
• This property significantly extends the lifespan of galvanized materials.
• Applications of Galvanized Metals
• Galvanized steel is commonly used in construction, automotive, and electrical industries.
• Examples include roofing materials, car bodies, and electrical boxes.

CONCEPT:

Conductivity and Ionization Constant (Ka)

• The conductivity (κ ) of a solution is related to the molar conductivity (Λm ) and the concentration (c) of the electrolyte.
• The relationship is given by:

Λm=κc

• Molar conductivity at infinite dilution (Λ∘m ) is the conductivity of an electrolyte at such a low concentration that further dilution does not change its molar conductivity.
• The degree of ionization (α) of a weak electrolyte can be calculated using the formula:

α=ΛmΛ∘m

• The ionization constant (Ka ) is related to the degree of ionization (α) and the concentration (c) by:

Ka=cα2

EXPLANATION:

• Given:
• Concentration, c=0.001mol/L
• Conductivity, κ=2.0×10−5S/cm
• Molar conductivity at infinite dilution, Λ∘m=190S cm2/mol
• Calculate molar conductivity (Λm ):
• Λm=κc
• Λm=2.0×10−5S/cm0.001mol/L
• Λm=2.0×10−2S cm2/mol
• Calculate degree of ionization (α):
• α=ΛmΛ∘m
• α=2.0×10−2S cm2/mol190S cm2/mol
• α=2.0×10−2190
• α=1.05×10−4
• Calculate ionization constant (Ka ):
• Ka=cα2
• Ka=0.001×(1.05×10−4)2
• Ka=0.001×1.1025×10−8
• Ka=1.1025×10−11
• Ka=11×10−12
• Ka=12×10−12≈12×10−6

Therefore, the ionization constant (Ka ) of HA is approximately 12 × 10^-6.