Chemical Reactions & Equations

1. A dilute solution of NaOH is added to a test tube containing some drops of phenolphthalein solution. The color of the solution changes to pink. What will be the color of the final solution when dilute HCl is added dropwise to the same test tube till it is in excess? (2024)

2. You are given an aqueous solution of a mixture of three salts, S1, S2, and S3. S1 is lead nitrate, S2 is sodium sulphate, and S3 is potassium chloride. What will be observed on mixing the aqueous solutions of S1 and S2? (2024)

3. The substances that produce heat and light on combustion are called: (2024)

4. Why do we store silver chloride in dark colored bottles? (2024)

5. The products formed when Aluminium and Magnesium are burnt in the presence of air respectively are: (2025)
   (A) Al304 and MgO2
   (B) Al2O3 and MgO
   (C) AI3O4 and MgO
   (D) Al2O3 and MgO2

6. Electrolysis of water is a decomposition reaction. The mass ratio (MH: MO) of hydrogen and oxygen gases liberated at the electrodes during electrolysis of water is: (2025)
   (A) 8:1
   (B) 2:1
   (C) 1:2
   (D) 1:8

7. Assertion (A): Decomposition reactions are generally endothermic reactions. 

Reason (R): Decomposition of organic matter into compost is an exothermic process. (2025)

1. A student performs the following experiment in his school laboratory. List two observations to justify that in this experiment a chemical change has taken place. (2025)

2. State two precautions which should be taken while burning a magnesium ribbon in air. Also, mention two observations of this activity. (2025)

3. When an aqueous solution of sodium sulphate is mixed with an aqueous solution of barium chloride, a chemical reaction occurs. (2025)
   (a) What is the color of the precipitate formed?
   (b) Name the type of chemical reaction.
   (c) Write a balanced chemical equation for the reaction.

4. Write balanced chemical equations for the reactions of: (2025)
   (i) Solid calcium oxide with water.
   (ii) Magnesium ribbon burnt in air.
   (iii) Copper carbonate with dilute hydrochloric acid.

5. What is a redox reaction? Give an example. (2023)

6. Why is the electrolysis of aqueous sodium chloride not used to obtain sodium metal? (2023)

7. State the type of chemical reactions that occur in the following examples: (a) Digestion of food in our body. (b) Rusting of an iron object. (2023)

8. Write the chemical equations for the reactions taking place when: (a) Zinc carbonate is heated in a limited supply of air. (b) Cinnabar is heated in air. (2023)

9. A student was given an aqueous solution of sodium carbonate in a test tube. He added a few drops of dilute hydrochloric acid to it. What will he observe? Write a balanced chemical equation for the reaction. (2023)

10. How can we balance a chemical equation? Explain with the help of an example. (2023)

11. A student mixed an aqueous solution of lead nitrate with potassium iodide in a test tube. (a) What color precipitate is formed? (b) Name the type of reaction. (c) Write a balanced chemical equation for the reaction. (2023)

12. Distinguish between homogeneous and heterogeneous mixtures with one example of each. (2023)

13. Choose the pair of olfactory indicators from the following: (2023)

14. A student adds a few pieces of silver metal to a test tube containing zinc sulphate solution. What will he observe? (2023)

15. A student takes four test tubes containing solutions of copper sulphate, ferrous sulphate, zinc sulphate and aluminium sulphate. He adds a few pieces of lead metal to each of the test tubes. To which test tube will he observe a change? (2023)