Science Class Notes: Complete Question Bank

Comprehensive practice flashcards created from full science lecture notes covering chemistry, biology, and physics questions.

What is valency?

The combining capacity of an element with other elements to form a compound is called valency (e.g., Valency of Sodium ($Na$) is $1$).

What is variable valency?

The property of an element by which it shows more than one valency in different compounds is called variable valency (e.g., Copper ($Cu$) shows valency $1$ and $2$, Iron ($Fe$) shows valency $2$ and $3$).

What are two key differences between an atom and an ion?

1. An atom is electrically neutral, whereas an ion is electrically charged. 2. An atom has an equal number of protons and electrons, whereas an ion has an unequal number of protons and electrons.

What is a radical and what are its main types?

An atom or a group of atoms carrying a positive or negative charge that acts as a single unit in a chemical reaction is called a radical. Types: Basic radical / Cation (positively charged, e.g., $Na^+$) and Acidic radical / Anion (negatively charged, e.g., $Cl^-$).

What is a molecular formula and what information is obtained from it?

The symbolic representation of a molecule showing the actual number of atoms of each element present in it. Information obtained: i) Name of elements present in the compound, ii) Number of atoms of each element present in one molecule.

What is the difference between a word equation and a chemical equation?

A word equation expresses a chemical reaction using the names of reactants and products (e.g., Hydrogen + Oxygen $\rightarrow$ Water). A chemical equation expresses it using chemical symbols and molecular formulas (e.g., $2H_2 + O_2 \rightarrow 2H_2O$).

What are two differences between a balanced and an unbalanced chemical equation?

1. In a balanced chemical equation, the number of atoms of each element on both sides is equal, whereas in an unbalanced equation, it is not equal. 2. A balanced equation obeys the law of conservation of mass, whereas an unbalanced equation does not.

What is a chemical bond and what are its main types?

The force of attraction that holds atoms or ions together to form a molecule or compound is called a chemical bond. Main types: Electrovalent (Ionic) bond, Covalent bond, and Coordinate covalent bond.

What is an electrovalent bond?

The chemical bond formed by the complete transfer of one or more electrons from one atom to another (e.g., Formation of Sodium chloride, $NaCl$).

What is a covalent bond?

The chemical bond formed by the mutual sharing of electron pairs between two atoms (e.g., Formation of Hydrogen molecule, $H_2$).

What does the Law of Conservation of Mass state?

It states that matter can neither be created nor destroyed in a chemical reaction; the total mass of reactants is equal to the total mass of products.

What is the difference between exothermic and endothermic reactions?

Exothermic Reaction: A reaction in which heat energy is released (e.g., $C + O_2 \rightarrow CO_2 + \text{Heat}$). Endothermic Reaction: A reaction in which heat energy is absorbed (e.g., $N_2 + O_2 + \text{Heat} \rightarrow 2NO$).

What is a catalyst and what are its types?

A chemical substance that alters the rate of a chemical reaction without undergoing any permanent chemical change itself. Positive Catalyst: Increases rate of reaction (e.g., $MnO_2$ in decomposition of $KClO_3$). Negative Catalyst: Decreases rate of reaction (e.g., Glycerol in decomposition of $H_2O_2$).

Define promoter and poison in catalysis.

Promoter: Increases efficiency of a catalyst (e.g., Molybdenum, $Mo$, in Haber's process). Poison: Decreases or destroys activity of a catalyst (e.g., Carbon monoxide, $CO$).

What is the principle of laboratory preparation of Hydrogen gas?

Hydrogen gas is prepared in the lab by treating granulated zinc with dilute hydrochloric acid or dilute sulphuric acid: $Zn + 2HCl \rightarrow ZnCl_2 + H_2\rightarrow$

How and why is Hydrogen gas collected in the laboratory?

Hydrogen gas is collected by downward displacement of water because it is nearly insoluble in water and lighter than air.

What are the physical and chemical properties of Hydrogen?

Physical: Colorless, odorless gas; lighter than air. Chemical: Burns with a pale blue flame to form water ($2H_2 + O_2 \rightarrow 2H_2O$); acts as a reducing agent.

What are two main uses of Hydrogen gas?

i) Used in the manufacture of ammonia gas. ii) Used as a fuel in rockets.

How is Oxygen gas prepared in the laboratory without heating?

Prepared by decomposing hydrogen peroxide ($H_2O_2$) using manganese dioxide ($MnO_2$) as a catalyst: $2H_2O_2 \rightarrow 2H_2O + O_2\rightarrow$

How is Oxygen gas prepared in the laboratory by heating?

Prepared by heating a mixture of potassium chlorate ($KClO_3$) and manganese dioxide ($MnO_2$) in the ratio $4:1$: $2KClO_3 \rightarrow 2KCl + 3O_2\rightarrow$

How and why is Oxygen gas collected in the laboratory?

Collected by downward displacement of water because it is slightly soluble in water.

What are the physical and chemical properties of Oxygen?

Physical: Colorless, odorless; slightly heavier than air. Chemical: Strong supporter of combustion; reacts with metals to form oxides.

What are two main uses of Oxygen gas?

i) Essential for respiration of living organisms. ii) Used in oxy-acetylene flames for welding.

What is the principle of laboratory preparation of Nitrogen gas?

Prepared by heating a mixture of ammonium chloride ($NH_4Cl$) and sodium nitrite ($NaNO_2$): $NH_4Cl + NaNO_2 \rightarrow NaCl + 2H_2O + N_2\rightarrow$

Why is ammonium nitrite not heated directly to prepare Nitrogen gas?

Ammonium nitrite ($NH_4NO_2$) is explosive and dangerous when heated directly; hence a mixture of $NH_4Cl$ and $NaNO_2$ is used.

How and why is Nitrogen gas collected in the laboratory?

Collected by downward displacement of water because it is almost insoluble in water.

What are the physical and chemical properties of Nitrogen?

Physical: Colorless, odorless gas; slightly lighter than air. Chemical: Neither combustible nor supporter of combustion; forms ammonia with hydrogen.

What are two uses of Nitrogen gas?

i) Used in manufacturing artificial nitrogenous fertilizers. ii) Used to create an inert atmosphere in electric bulbs.

What is taxonomy?

The branch of biology concerned with the identification, naming, and classification of organisms is called taxonomy.

What are the five kingdoms proposed by Whittaker?

Monera, Protista, Fungi, Plantae, Animalia.

What are two features of Kingdom Monera?

i) Prokaryotic, unicellular organisms. ii) Lack a well-defined nucleus and membrane-bound organelles.

What are two features of Kingdom Fungi?

i) Non-green, eukaryotic organisms with saprophytic or parasitic nutrition. ii) Cell wall is made up of chitin.

What are two features of Kingdom Plantae?

i) Multicellular, eukaryotic, autotrophic organisms containing chlorophyll. ii) Cell wall is made up of cellulose.

What are two features of Kingdom Animalia?

i) Multicellular, eukaryotic organisms without cell walls. ii) Heterotrophic mode of nutrition with holozoic feeding.

What compound and bond type are formed when Sodium (A, valency 1) reacts with Sulphur (B, valency 2)?

The compound formed is Sodium sulphide ($Na_2S$) and the bond formed is an electrovalent bond.

What are two differences between a sodium atom and a sodium ion?

1. A sodium atom is a highly reactive chemical element, whereas a sodium ion is chemically stable. 2. The electronic configuration of a sodium atom is $2, 8, 1$, whereas that of a sodium ion is $2, 8$.

What precautions must be taken during the laboratory preparation of ammonia gas?

i) Molar quantity of Ammonium chloride & Sodium nitrite needs to be equal. ii) Collect by downward displacement of air using an inverted gas jar.

Which lab preparation of oxygen is more effective and why?

The heating method, because the reaction becomes much quicker.

What are the key differences between electrovalent and covalent compounds?

Electrovalent compounds are made of ions and can be electrolyzed. Covalent compounds are made of molecules and cannot be electrolyzed.

Why was nitrogen historically called 'azote'?

It was called 'azote' meaning 'no life'.

What four pieces of information can be obtained from a balanced chemical equation?

i) Type of chemical reaction. ii) Symbols & formulas. iii) Exact reactants and products. iv) Number of moles of each substance.

Why can pure zinc not be used in the laboratory preparation of hydrogen gas?

Pure zinc reacts extremely slowly with dilute acids.

What happens when KClO3 is heated with vs without a catalyst?

Both produce $KCl$ and Oxygen, but the $MnO_2$ catalyst speeds up the reaction significantly.

What is the binomial system of nomenclature?

The formal system of naming species of living things by giving each a name composed of two parts (Genus and Species).

Who is the father of taxonomy?

Carl Linnaeus.

What is the scientific name of the frog?

Rana tigrina.

What are the scientific names of mustard and tiger?

Mustard: Brassica campestris; Tiger: Panthera tigris.

Why do protozoa belong to Kingdom Protista?

Because protozoa are unicellular eukaryotic organisms with a true nucleus.

What are two reasons for classifying mushrooms in Kingdom Fungi?

i) Eukaryotic, non-green, saprophytic/multicellular. ii) Reproduces via spore formation.

What are two drawbacks of the two-kingdom system of classification?

i) Classified organisms only into Plants and Animals. ii) No distinction between unicellular and multicellular or prokaryotes and eukaryotes.

What is a similarity and a dissimilarity between algae and fungi?

Similar: Both are eukaryotes. Dissimilar: Algae are autotrophic (contain chlorophyll); Fungi are heterotrophic.

What are the similarities and dissimilarities between Kingdom Protista and Kingdom Fungi?

Similarities: Both are eukaryotic and heterotrophic. Dissimilarities: Protista is unicellular; Fungi is multicellular.

To which kingdoms do Paramecium, Bacteria, Hydra, and Mustard plant belong?

1. Paramecium: Protista. 2. Bacteria: Monera. 3. Hydra: Animalia. 4. Mustard plant: Plantae.

Why is a wheel and axle called a continuous lever?

Because the wheel and axle rotate continuously around a common fulcrum. It is used to lift heavy loads.

What does 75% efficiency mean for a machine, and what is the VR of a single movable pulley?

75% efficiency means $75\text{\%}$ work is converted into output and $25\text{\%}$ is lost to friction. The VR of a single movable pulley is $2$ because the load is supported by two rope segments.

Define Mechanical Advantage (MA) and Velocity Ratio (VR).

MA: Ratio of Load to Effort ($\frac{L}{E}$). VR: Ratio of Effort Distance to Load Distance ($\frac{d_E}{d_L}$).

Why is the efficiency of a practical machine always less than 100%?

Due to energy losses caused by friction between moving parts and the weight of machine components.

What is an ideal machine?

A machine with $100\text{\%}$ efficiency where output work equals input work.

What is the formula relating MA, VR, and Efficiency (η)?

$$\eta = \left(\frac{\text{MA}}{\text{VR}}\right) \times 100\%$$

What defines a first-class, second-class, and third-class lever?

First-class: Fulcrum lies between effort and load (e.g., Scissors, Crowbar). Second-class: Load lies between fulcrum and effort (e.g., Wheelbarrow, Nutcracker). Third-class: Effort lies between fulcrum and load (e.g., Sugar tongs, Human forearm).

Why is Velocity Ratio (VR) always greater than Mechanical Advantage (MA) in real life?

Friction reduces MA, whereas VR depends purely on physical dimensions and remains constant.

Define work, energy, and power.

Work: $W = F \times d$. Energy: Capacity to do work. Power: Rate of doing work ($P = \frac{W}{t}$).

What are the SI units of Work, Energy, and Power?

Work & Energy: Joule ($J$); Power: Watt ($W$).

Define 1 Watt of power.

$1\text{\,Watt}$ is the power when $1\text{\,Joule}$ of work is performed in $1\text{\,second}$.

How do Kinetic Energy and Potential Energy differ?

Kinetic Energy is energy due to motion ($\text{KE} = \frac{1}{2}mv^2$), whereas Potential Energy is energy due to position or shape ($\text{PE} = mgh$).

State the Principle of Conservation of Energy.

Energy can neither be created nor destroyed; it can only be transformed from one form to another.

Define 1 Joule of work.

Work done when $1\text{\,Newton}$ force displaces an object by $1\text{\,meter}$ in the force's direction.

Calculate the work done when F = 50 N and d = 10 m.

Given $F = 50\text{\,N}$ and $d = 10\text{\,m}$, $W = F \times d = 50 \times 10 = 500\text{\,Joules}$.