Sslc Chemistry Exam Answer Key 2025

CHEMISTRY ANSWER KEY

SSLC Exam 2025

1. Which of the given compounds is a mineral of Aluminium?
   Answer: Cryolite
2. Which polymer is formed from isoprene?
   Answer: Natural rubber (or Polyisoprene)
3. Find the total number of atoms in 2 GMM water (H₂O).
   Answer:
   • 1 molecule of H₂O contains 3 atoms (2 Hydrogen + 1 Oxygen)
   • 2 GMM = 2 × 6.022 × 10²³ molecules = 1.2044 × 10²⁴ molecules
   • Total atoms = 1.2044 × 10²⁴ × 3 = 3.6132 × 10²⁴ atoms
4. Which is the product obtained when SO₃ gas is dissolved in concentrated sulphuric acid?
   Answer: Oleum
5. Many of the metals in _______ block are used as catalysts in the petroleum industry.
   Answer: d-block
6. Classify the following compounds into alkanes, alkenes, and alkynes:
   Compounds: C₂H₄, C₅H₁₂, C₃H₈, C₇H₁₂
   Answer:
   • Alkanes: C₅H₁₂ (Pentane), C₃H₈ (Propane)
   • Alkenes: C₂H₄ (Ethene)
   • Alkynes: C₇H₁₂ (Heptyne)
7. Two gases Oxygen and Nitrogen at STP are given:
   (a) Calculate the number of molecules in 64 g of Oxygen.
   
   • Molecular mass of O₂ = 32
   • Number of moles = 64 / 32 = 2 moles
   • Molecules = 2 × 6.022 × 10²³ = 1.2044 × 10²⁴ molecules

(b) Calculate the mass of Nitrogen having the same volume as that of 64 g of Oxygen.

• 64 g of O₂ = 2 moles = 2 × 22.4 L = 44.8 L (at STP)
• 44.8 L of N₂ = 2 moles (since 1 mole = 22.4 L)
• Mass of N₂ = 2 × 28 = 56 g

8. Two reactions related to extraction of metals are given. Identify calcination and roasting.

(a) Cu₂S ore is converted to Cu₂O by heating.

This is Roasting (as it involves heating of sulphide ore in presence of oxygen).

(b) Carbonates and hydroxides of metals decompose to form the oxides.

This is Calcination (as it involves heating in absence of air).

9. Identify A and B.

(a) CH₃OH + CO →(catalyst)→ (A)

This forms CH₃COOH (Acetic acid)

A = CH₃COOH

(b) CHCl₃ + Cl₂ → (B) + HCl

This forms CCl₄ (Carbon tetrachloride)

B = CCl₄

10. The chemical formula of a compound is C₂H₆O.

(a) Write the structural formula of any one of the functional isomers.

Two functional isomers:

• Ethanol: CH₃–CH₂–OH
• Dimethyl ether: CH₃–O–CH₃

(b) Write the IUPAC name of this functional isomer.

If ethanol: Ethanol

If dimethyl ether: Methoxymethane

11. Copper is electroplated on an iron bangle.

(a) Which electrolyte is used here?

Copper sulphate (CuSO₄) solution

(b) Write any one of the advantages of electroplating.

• Improves appearance
• Prevents corrosion
• Increases durability

(c) Does the intensity of colour of electrolyte change during this process? Why?

Yes, the intensity decreases because Cu²⁺ ions are deposited on the iron and their concentration in the solution reduces.

12. Subshell electronic configuration of element 'A' is given.

1. 1s² 2s² 2p⁶ 3s² 3p⁶ 3d²
2. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

(a) Which is the correct subshell electronic configuration? Why?

(ii) is correct

Because 4s orbital is filled before the 3d orbital.

(b) Identify the block in the periodic table to which this element belongs.

Ends in 4s² → s-block

13. Two reversible reactions are given:

1. H₂(g) + I₂(g) ⇌ 2HI(g) + Heat
2. 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) + Heat

(a) Identify the reaction in which pressure has no effect.

Reaction I (equal number of moles of gas on both sides → pressure has no effect)

(b) How do the following factors influence the amount of product in Reaction II?

(i) Increase the temperature

Decreases the amount of SO₃ (forward reaction is exothermic, heat opposes forward direction)

(ii) Increase the pressure

Increases the amount of SO₃ (forward reaction has fewer gas molecules)

14. (a) Which types of reactions are these?

1. Addition reaction
2. Polymerisation reaction

(b) Identify the product in the reaction (ii) and write any one use of it.

Product: Polyvinyl chloride (PVC)

Use: Used in making pipes, wires, cables, synthetic leather, etc.

15. Volume and number of molecules of gases at 27°C and 2 atm:

Gas	Volume (L)	Number of molecules
Nitrogen	10	x
Carbon dioxide	20	2x
Oxygen	5	0.5x

(a) Complete the table.

Use Avogadro’s Law: Equal volumes of gases at the same temperature & pressure have equal number of molecules.

If 10 L = x molecules, then:

• CO₂ = 20 L → 2x molecules
• O₂ = 5 L → 0.5x molecules

(b) What will be the volume of carbon dioxide gas if pressure is increased to 4 atm?

At constant T and n, P₁V₁ = P₂V₂

P₁ = 2 atm, V₁ = 20 L

P₂ = 4 atm

V₂ = (P₁ × V₁) / P₂ = (2 × 20) / 4 = 10 L

16. Manganese (Mn) is an element that belongs to d block in the periodic table.

(a) Outer subshell electronic configuration of Mn is 3d⁵4s²3d⁵4s². Find the atomic number of Manganese.

Answer: Atomic number = 25

(b) Find the oxidation state of Mn in Mn₂O₇.

Answer: +7

(c) Write period number and group number of Manganese.

Answer: Period = 4, Group = 7

(d) Write the subshell electronic configuration of Mn⁴⁺ ion.

Answer: 1s²2s²2p⁶3s²3p⁶3d³

17. A few drops of the solution ‘X’ is added to Magnesium sulphate solution taken in a test tube. A white precipitate is formed.

(a) What is ‘X’?

Answer: Sodium hydroxide (NaOH)

(b) What is the chemical name of white precipitate formed here?

Answer: Magnesium hydroxide (Mg(OH)₂)

(c) What happens to the white precipitate when dilute hydrochloric acid is added?

Answer: It dissolves to form a clear solution.

(d) Which type of salt is identified by this experiment?

Answer: Magnesium sulphate (MgSO₄)

18. Three metals Ag, Mg, Cu and their salt solutions are given.

(a) How many galvanic cells can be constructed using these metals?

From 3 metals, possible pairs = 3C2 = 3 galvanic cells

(b) If we construct a galvanic cell using the most reactive metal and the least reactive metal from the given metals, identify the cathode and anode.

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Reactivity order: Mg > Cu > Ag

Anode = Mg (most reactive → oxidized)

Cathode = Ag (least reactive → reduced)

(c) Write the chemical equation of the reaction which takes place at anode and cathode in the above cell.

At Anode (Mg):

Mg → Mg²⁺ + 2e^-

At Cathode (Ag):

Ag⁺ + e^- → Ag

(But since two electrons come from Mg, it would be: 2Ag⁺ + 2e^- → 2Ag)

Overall cell reaction:

Mg + 2Ag⁺ → Mg²⁺ + 2Ag

19. (a) Write the name and chemical formula of ore of iron used in industrial production.

Name: Haematite

Formula: Fe₂O₃

(b) Write the chemical equation of slag formation in the industrial production of iron.

CaO + SiO₂ → CaSiO₃ (slag)

(c) Which mineral of iron is known as fool’s gold?

Answer: Iron pyrite or FeS₂

(d) Write the names of two alloy steels which contain the same constituent elements.

Answer: Stainless steel and Tungsten steel (both contain Fe, C, and other metals like Cr, W, etc.)

20.

A (Structure)	B (Molecular Formula)	C (Name)
CH3-CH-CH-CH3 (CH3 on both C2 and C3)	C6H14	2,3-Dimethylbutane
CH3-CH=CH-CH3	C4H8	But-2-ene
CH3-CH(OH)-CH3	C3H8O	Propan-2-ol
CH3-CH2-CH2-CH2-COOH	C5H10O2	Pentanoic acid