CHEMISTRY ANSWER KEY
SSLC Exam 2025
- Which of the given compounds is a mineral of Aluminium?
Answer: Cryolite - Which polymer is formed from isoprene?
Answer: Natural rubber (or Polyisoprene) - 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
- Which is the product obtained when SO3 gas is dissolved in concentrated sulphuric acid?
Answer: Oleum - Many of the metals in _______ block are used as catalysts in the petroleum industry.
Answer: d-block - 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)
- 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.
- 1s2 2s2 2p6 3s2 3p6 3d2
- 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:
- H2(g) + I2(g) ⇌ 2HI(g) + Heat
- 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?
- Addition reaction
- 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.
!DOCTYPE html>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 |