Comprehensive Science Exam Study Guide 2025

Chemical Reactions and Metals (Code 31/6/1 & 31/5/1)

Displacement Reactions and Reactivity Series

In an experimental setup, a light green coloured solution of a sulphate salt of metal 'P' is placed in a beaker. A rod of another metal 'Q' is placed in the solution. After approximately one hour, the solution becomes colourless, forming a new sulphate solution $QSO_4$ .

Identification of Metals:
- Metal 'P': Iron ( $Fe$ ). The light green solution is Ferrous Sulphate ( $FeSO_4$ ).
- Metal 'Q': Zinc ( $Zn$ ). Zinc displaces iron to form a colourless solution of Zinc Sulphate ( $ZnSO_4$ ).
Chemical Equation: $Zn(s) + FeSO_4(aq) \rightarrow ZnSO_4(aq) + Fe(s)$
Conclusion regarding Reactivity Series: Metal 'Q' (Zinc) is more reactive than metal 'P' (Iron). This reaction is a displacement reaction, where a more reactive metal displaces a less reactive metal from its salt solution.

Electrolytic Refining of Copper

In the process of electrolytic refining of copper, the specific components used are:

Anode: Impure copper.
Cathode: Pure copper.
Electrolyte: Acidified copper sulphate solution.

Reaction of Metal 'X' with Acids and Bases

A metal 'X' reacts with both sodium hydroxide ( $NaOH$ ) and dilute sulphuric acid ( $H_2SO_4$ ) to liberate the same gas 'G'.

Identification: Metal 'X' is Zinc ( $Zn$ ) and gas 'G' is Hydrogen ( $H_2$ ).
Reactions:
- With Base: $Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2$
- With Acid: $Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2$

Acids, Bases, and Salts (Code 31/6/1 & 31/5/2)

Water of Crystallization

Water of crystallization is the fixed number of water molecules present in one formula unit of a salt. Based on the provided options:

Bleaching Powder: $CaOCl_2$ (No water of crystallization).
Plaster of Paris: $CaSO_4 \cdot \frac{1}{2}H_2O$ (Contains water of crystallization).
Washing Soda: $Na_2CO_3 \cdot 10H_2O$ (Contains water of crystallization).
Baking Soda: $NaHCO_3$ (No water of crystallization).

Correct pair: (ii) Plaster of Paris and (iii) Washing Soda.

pH Levels of Aqueous Solutions

Consider three aqueous solutions:

Solution A: Potassium nitrate ( $KNO_3$ ) - Neutral salt, $pH \approx 7$ .
Solution B: Ammonium chloride ( $NH_4Cl$ ) - Salt of a strong acid ( $HCl$ ) and weak base ( $NH_4OH$ ), Acidic, $pH < 7$ .
Solution C: Sodium carbonate ( $Na_2CO_3$ ) - Salt of a strong base ( $NaOH$ ) and weak acid ( $H_2CO_3$ ), Basic, $pH > 7$ .
Ascending Order of pH: $B < A < C$ (Ammonium chloride < Potassium nitrate < Sodium carbonate).

Distinguishing Alcohol and Carboxylic Acid

To distinguish between an alcohol (e.g., Ethanol) and a carboxylic acid (e.g., Ethanoic acid), the sodium bicarbonate ( $NaHCO_3$ ) test can be performed.

Process: Add a pinch of sodium hydrogencarbonate to both compounds.
Observation: Carboxylic acid reacts with sodium hydrogencarbonate to produce brisk effervescence due to the evolution of Carbon dioxide ( $CO_2$ ). Alcohol does not react.
Chemical Equation: $CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2 \uparrow$

Carbon and Its Compounds (Code 31/5/2)

Structural Isomers of Butane

Structural isomers are compounds that have the same molecular formula but different structural arrangements of atoms.

Molecular Formula of Butane: $C_4H_{10}$
Isomer 1 (n-butane): A straight chain of four carbon atoms. $CH_3-CH_2-CH_2-CH_3$
Isomer 2 (Iso-butane/2-methylpropane): A branched chain. $CH_3-CH(CH_3)-CH_3$

Addition Reactions in Hydrocarbons

Two compounds are examined: $X (C_2H_4)$ , which is ethene (an alkene), and $Y (CH_4)$ , which is methane (an alkane).

Selection: Compound $X (C_2H_4)$ is most likely to show an addition reaction because it is an unsaturated hydrocarbon containing a double bond.
Chemical Equation (Hydrogenation): $CH_2=CH_2 + H_2 \xrightarrow{Ni/Pd} CH_3-CH_3$
Industrial Application: This reaction is applied in the vegetable oil industry for the hydrogenation of vegetable oils (liquid) into vegetable ghee (solid).

Homologous Series

A homologous series is a group of organic compounds having the same general formula and functional group, where successive members differ by a $-CH_2-$ group.

Series with Functional Group -CHO (Aldehydes):
1. Methanal ( $HCHO$ )
2. Ethanal ( $CH_3CHO$ )
3. Propanal ( $C_2H_5CHO$ )
4. Butanal ( $C_3H_7CHO$ )

Biology: Genetics, Life Processes, and Control (Code 31/6/1 & 31/5/1)

Mendelian Genetics: Dihybrid Cross

A tall pea plant with round seeds ( $TTRR$ ) is crossed with a short pea plant with wrinkled seeds ( $ttrr$ ).

F1 Generation: All offspring will have the genotype $TtRr$ .
Phenotype of F1: 100% tall with round seeds.

Human Endocrine System

A pair of endocrine glands located specifically in the human brain includes:

Pituitary Gland
Pineal Gland (Note: Hypothalamus also located there; options from transcript highlight Pituitary).

Nutrition in Amoeba

The sequence of steps for nutrition in Amoeba is as follows:

Formation of finger-like temporary extensions of cell surface (Pseudopodia).
Food vacuole formation.
Complex substances broken down into simpler ones.
Diffusion of simple nutrients into cytoplasm.
Undigested material thrown out of the cell surface.

Respiration and Energy

In aerobic respiration, the breakdown of glucose occurs in two primary locations:

Step 1: Glucose to Pyruvate (occurs in the Cytoplasm).
Step 2: Pyruvate to Carbon dioxide and water (occurs in the Mitochondria).

Reproduction and Development

Nutrition of Embryo: The embryo receives nutrition from the mother's blood through the Placenta. This is a special disc-like tissue embedded in the uterine wall.
Chromosomes: Specialized structures made of DNA and proteins that carry genetic information.
Sex Chromosomes in Males: Referred to as a mismatched pair ( $XY$ ) because the 'Y' chromosome is smaller than the 'X' chromosome, unlike the perfect pair ( $XX$ ) in females.
Sex Determination Probability: In humans, there is a statistical probability of 50:50 for a boy or a girl. This is determined by whether the sperm carrying an 'X' or 'Y' chromosome fertilizes the egg (which always carries an 'X').
Non-Genetic Sex Determination: In some animals like snails, sex can change, indicating it is not genetically fixed. In some reptiles (e.g., turtles), the incubation temperature of eggs determines the sex.

Respiratory Pigments

Name: Haemoglobin.
Function: It has a high affinity for oxygen and transports it from the lungs to various tissues in the body.

Physics: Electricity, Magnetism, and Optics (Code 31/5/3, 31/5/2, & 31/5/1)

Magnetic Field and Conductors

For a current-carrying conductor in a uniform magnetic field:

Factors affecting Force ( $F$ ):
1. Magnitude of current ( $I$ ).
2. Strength of the magnetic field ( $B$ ).
3. Length of the conductor ( $L$ ).
4. Orientation (angle) of the conductor in the magnetic field.
Maximum Force: Occurs when the conductor is placed perpendicular (at right angles) to the direction of the magnetic field.
Rule for Direction: Fleming's Left Hand Rule. Application: Used in electric motors.

Short Circuiting

Definition: Short circuiting occurs when the live wire and neutral wire come into direct contact.
Causes: Damaged insulation, fault in electrical appliances, or overloading.
Consequence: An abrupt increase in current leads to excessive heating, causing the fuse wire to melt and break the circuit, thereby preventing fire or damage.

Ohm's Law and Circuit Calculations

Ohm's Law: $V = I \times R$ .
Power Dissipation Proof: $P = I^2 \times R$ If current $I$ increases by 100%, the new current $I' = 2I$ . New Power $P' = (2I)^2 \times R = 4I^2R = 4P$ . Increase in Power = $P' - P = 3P$ . Percentage Increase = $\frac{3P}{P} \times 100 = 300\%$ .
Resistance Calculation: Given radius $r = 0.01\,cm = 0.01 \times 10^{-2}\,m$ and $R = 7\,\Omega$ . Area $A = \pi r^2$ .

Optics and Refractive Index

Comparison between Kerosene ( $n = 1.44$ ) and Water ( $n = 1.33$ ):

Property	Kerosene ( $1.44$ )	Water ( $1.33$ )
Optical Density	Higher	Lower
Mass Density	Lower	Higher
Relative Speed of Light	Lower	Higher

Inference: An optically denser medium (like kerosene) does not necessarily have a higher mass density than an optically rarer medium (like water).
Dental Mirrors: Dentists use concave mirrors. To see a large (enlarged) image of teeth, the teeth must be positioned between the pole and the focus of the mirror.

Corrosion of Metals

In an experiment to determine corrosion conditions for metal 'M' (protected by galvanisation):

Case A (Moist Air + Oil/Water): Metal M corrodes partly. The part exposed to moist air corrodes, while the submerged part is protected from air.
Case B (Inside Oil): No corrosion occurs as the metal is not exposed to moist air.
Case C (Dry Air): No corrosion occurs because moisture (water) is absent.

Ionic Compounds

Formation example (Aluminium Nitride - AlN):
- $Al$ (Atomic No. 13): Electronic config $2, 8, 3$ . Loses 3 electrons to become $Al^{3+}$ .
- $N$ (Atomic No. 7): Electronic config $2, 5$ . Gains 3 electrons to become $N^{3-}$ .
Properties: Ionic compounds are solids and brittle because they have strong interionic electrostatic forces of attraction holding the lattice together. Pressure causes like-charged ions to come close and repel, breaking the crystal.