Answer: D. Both equations 1 and 2 are redox reactions, p = 2 and q = 10
Explanation:
Equation 1: This is a redox reaction known as the displacement reaction (Thermite reaction). Aluminum is oxidized, and iron(III) oxide is reduced. p = 2 because 2 Fe atoms are produced.
Equation 2: This is a combustion reaction of butane (C4H10) and is also a redox reaction. q = 10 because 10 H2O molecules are formed (from 20 hydrogen atoms in 2 butane
Q18. Four statements about the reactions of oxides with dilute hydrochloric acid and aqueous sodium hydroxide are listed.
Aluminium oxide reacts with both dilute hydrochloric acid and aqueous sodium hydroxide.
Calcium oxide reacts with dilute hydrochloric acid and aqueous sodium hydroxide.
Zinc oxide reacts with both dilute hydrochloric acid and aqueous sodium hydroxide.
Sulphur dioxide does not react with either dilute hydrochloric acid or aqueous sodium hydroxide.
Which statements are correct?
Answer: B. I and III
Explanation:
Statement I: Correct. Aluminium oxide is amphoteric — it reacts with both acids and bases.
Statement II: Incorrect. Calcium oxide is a basic oxide. It reacts only with acids, not with bases.
Statement III: Correct. Zinc oxide is also amphoteric and reacts with both acids and alkalis.
Statement IV: Incorrect. Sulphur dioxide is an acidic oxide; it reacts with bases like sodium hydroxide.
Q19. An iron nail is added to each of the two test tubes ‘P’ and ‘Q’ containing aqueous copper (II) sulphate, and aqueous silver nitrate respectively. Which of the following observation is correct?
A. In test tube ‘P’ iron nail is coated with a blue coating and in test tube ‘Q’ there is no reaction.
B. Iron nail is coated with a brown coating in test tube ‘P’ and silver coating in test tube ‘Q’.
C. There is no reaction in either of the test tubes ‘P’ or ‘Q’.
D. There is no reaction in test tube ‘P’ but a silver coating on iron nail is seen in test tube ‘Q’.
Answer: B. Iron nail is coated with a brown coating in test tube ‘P’ and silver coating in test tube ‘Q’.
Explanation:
In test tube P (Copper(II) sulphate): Iron is more reactive than copper. It displaces copper from the solution, forming iron sulphate. Copper gets deposited on the nail as a brown coating.
In test tube Q (Silver nitrate): Iron is also more reactive than silver. It displaces silver from the solution, and silver gets deposited on the nail as a shiny grey/silver coating.
Q20. Methyl orange is added to dilute hydrochloric acid and to aqueous sodium hydroxide. What is the colour of the methyl orange in each solution?
Sample
Colour in dilute hydrochloric acid
Colour in aqueous sodium hydroxide
A
Orange
Red
B
Red
Yellow
C
Red
Orange
D
Yellow
Red
Answer: B. Red in dilute hydrochloric acid and Yellow in aqueous sodium hydroxide
Explanation:
Methyl orange is a pH indicator.
In acidic solutions (like dilute HCl), it turns red.
In basic solutions (like NaOH), it turns yellow.
Q21. Which of the following substances when dissolved in equal volume of water, will have the highest pH value?
A. Sulphuric acid
B. Acetic acid
C. Magnesium hydroxide
D. Sodium hydroxide
Answer: D. Sodium hydroxide
Explanation: Sodium hydroxide is a strong alkali and fully dissociates in water, giving the highest concentration of OH– ions, hence the highest pH.
Q22. When excess of carbon dioxide is passed through lime water, the milkiness disappears because
A. water soluble calcium carbonate converts to water soluble calcium bicarbonate.
B. insoluble calcium carbonate converts to water soluble calcium bicarbonate.
C. water soluble calcium carbonate converts to insoluble calcium bicarbonate.
D. insoluble calcium carbonate converts to insoluble calcium bicarbonate.
Answer: B. insoluble calcium carbonate converts to water soluble calcium bicarbonate.
Explanation: When CO2 is passed in excess through lime water, the initially formed insoluble calcium carbonate (which causes milkiness) reacts further with CO2 and water to form soluble calcium bicarbonate, making the solution clear.
Q23. In the reaction of aqueous solution of barium chloride with aqueous solution of sodium sulphate, the aqueous solution formed will be:
A. BaCl2
B. BaSO4
C. Na2SO4
D. NaCl
Answer: D. NaCl
Explanation: When BaCl2 reacts with Na2SO4, a white precipitate of BaSO4 forms, and NaCl remains dissolved in the aqueous solution. Hence, NaCl is present in the final aqueous phase.
Q24. The following question consists of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below:
Assertion (A): C4H8, C4H6 and C4H10 are members of the same homologous series. Reason (R): C4H8, C4H6, C3H4, C3H6, C2H4, C2H2 are unsaturated hydrocarbons.
Options:
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, and R is not the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.
Answer: D. A is false but R is true.
Explanation:
Assertion: False. C4H6 (an alkyne), C4H8 (an alkene), and C4H10 (an alkane) belong to different homologous series because they have different functional groups and general formulas.
Reason: True. All the compounds listed (C4H8, C4H6, C3H4, etc.) are unsaturated hydrocarbons (alkenes or alkynes) except C4H10, which is saturated.
Q25. The following activity is set up in the science lab by the teacher:
He clamped an aluminium wire on a stand and fixed a pin to the free end of the wire using wax. Then he heated the wire with a burner from the end where the wire is clamped. Students observed the pin fall off.
Refer to image:
A. If the teacher replaces aluminium wire with silver wire, will the students’ observation change? Justify your answer.
Answer: Yes, the students’ observation may change in terms of time taken for the pin to fall off. Silver is a better conductor of heat than aluminium, so heat will reach the wax faster. As a result, the wax will melt more quickly and the pin will fall off sooner.
B. Will the aluminium wire melt? Give reason for your answer.
Answer: No, the aluminium wire will not melt in this activity. The melting point of aluminium is quite high (about 660°C), whereas the heat provided by a spirit lamp is not sufficient to reach that temperature. The experiment only requires enough heat to melt the wax, which melts at a much lower temperature (around 60–70°C).
Q26. Attempt either option A or B.
A. An element ‘X’ is stored in kerosene, and cannot be extracted from its ore using a reducing agent. ‘X’ forms an ionic compound on reaction with chlorine.
Can we store ‘X’ in water? Give reason to support your answer. Answer: No, we cannot store ‘X’ in water because it is highly reactive and reacts violently with water, producing hydrogen gas and heat, which may cause fire or explosion. That is why it is stored in kerosene to prevent its reaction with moisture or oxygen.
Identify element ‘X’. Name the process used and write the equation for extraction of ‘X’ from its ore. Answer: The element ‘X’ is sodium (Na). It is highly reactive and belongs to the alkali metal group.
Sodium is extracted by the process of electrolysis of molten sodium chloride (NaCl). Equation:
2NaCl(l) → 2Na(l) + Cl2(g)
Q27. Amrita electrolysed distilled water using the set-up shown in figure 1. She was expecting two gases to be evolved at the anode and cathode respectively.
Suddenly, she realised that the bulb in the circuit did not glow when she used distilled water (figure 2).
After this realization, she added a substance to the distilled water for electrolysis to take place.
A. Which gas was she expecting to be formed at the anode and which one at the cathode respectively? Answer: She was expecting:
– Oxygen gas at the anode
– Hydrogen gas at the cathode
This is because electrolysis of water produces hydrogen and oxygen gases. The reactions are:
At cathode: 2H⁺ + 2e⁻ → H₂
At anode: 2H₂O → O₂ + 4H⁺ + 4e⁻
B. Why did the bulb not glow when Amrita passed electricity through distilled water? Answer: Distilled water does not contain free ions and hence is a poor conductor of electricity. Since no current passes through the solution, the circuit remains incomplete and the bulb does not glow.
C. Which substance was added by Amrita to distilled water to get the expected result? Answer: Amrita added a few drops of dilute sulfuric acid (H₂SO₄) to the distilled water. Reason: Sulfuric acid increases the ion content in water by releasing H⁺ and SO₄²⁻ ions. This makes the solution conductive, allowing electricity to flow and electrolysis to occur.
Q28. Sara took 2 mL of dilute NaOH solution in a test tube and added two drops of phenolphthalein solution to it. The solution turned pink in colour. She added dilute H2SO4 to the above solution drop by drop until the solution became colourless. 40 drops of dilute H2SO4 were used. When Sara added a drop of NaOH again, the colour turned back to pink.
She repeated the activity with different volumes of NaOH and recorded the following data:
S. No.
Volume of dilute NaOH (mL)
Drops of dilute H2SO4 used
1
2
20
2
3
30
3
4
40
A. If Sara used concentrated H2SO4 instead of dilute H2SO4, how many drops would be required to change the colour?
Answer: (b) < 40 Justification: Concentrated H2SO4 has more H+ ions per drop than dilute acid. Therefore, fewer drops would be needed to neutralise the NaOH and change the pink colour to colourless.
B. Sara measured 20 drops of dilute H2SO4 to be 1 mL. If the solution turned colourless after using 3 mL of acid, how much NaOH did she initially add?
Answer: Each 1 mL of acid = 20 drops, so 3 mL = 60 drops.
From her observations, 20 drops of acid neutralised 2 mL of NaOH.
Thus, 60 drops would neutralise 6 mL of NaOH. So, Sara initially added 6 mL of NaOH.
OR
Sara takes 10 drops of dilute H2SO4 and adds two drops of phenolphthalein. Then she adds NaOH dropwise. She observes a colour change after 20 drops of NaOH. What change does she observe and why?
Answer: She observes a colour change from colourless to pink. Reason: Phenolphthalein is colourless in acidic medium. As NaOH neutralises the acid and makes the solution basic, the indicator turns pink.
C. Write a balanced chemical equation and identify the type of reaction.
Correct option: (a) neutralisation and double displacement reaction Explanation: The acid-base reaction between H2SO4 and NaOH is a neutralisation reaction (H+ + OH– → H2O). Since the ions are exchanged between two compounds, it is also a double displacement reaction.
Q29. Attempt either Option A or B
Option A: Hydrocarbon Combustion Reaction
Given: 2CxHy + 9O2 → 6CO2 + 6H2O
(a) What are the values of ‘x’ and ‘y’?
Answer: Comparing both sides, we get:
On RHS: 6 carbon atoms and 12 hydrogen atoms ⇒ x = 3, y = 6
So, the hydrocarbon is C3H6.
(b) Give the chemical (IUPAC) name of the hydrocarbon.
Answer: Propene (an unsaturated hydrocarbon – alkene group)
(c) Draw its electron dot structure.
Answer:
H H H
\ | /
C = C - C
/ \
H H
(You can insert a PNG or SVG of propene dot structure here on your WordPress site for better visual clarity)
(d) Name the alcohol which on heating with conc. H2SO4 will produce the above hydrocarbon C3H6.
Answer: Propan-2-ol
Reaction:
C3H7OH (Propan-2-ol) → C3H6 + H2O
(in presence of conc. H2SO4)
(e) Write a balanced chemical equation for the reaction of CxHy with hydrogen gas in presence of Nickel.
Answer:
C3H6 + H2 → C3H8 (Propane)
(In presence of Ni catalyst – hydrogenation reaction)
Option B: Based on Electronic Configuration of P and Q
(a) If P and Q combine to form a compound, what type of bond is formed between them?
Answer: Ionic bond
Explanation: Na donates one electron to form Na⁺ and O accepts two electrons to form O²⁻.
(b) Give the chemical formula of the compound formed.
Answer: Na2O
(c) The compound so formed is dissolved in water. Is the resultant solution acidic or basic in nature? Justify your answer.
Answer: Basic
Justification: Na2O + H2O → 2NaOH (Strong base)
(d) Write the chemical equation for the reaction between ‘Q’ and ethanol.
Answer:
2Na + 2C2H5OH → 2C2H5ONa + H2↑
(e) What will be the formula of the compound formed when ‘P’ undergoes bonding with carbon?
Answer: CO2 (Carbon Dioxide)
Justification: Carbon forms double bonds with two oxygen atoms. The compound formed is covalent.
