1.Define an acid and a base in terms of their chemical behaviour. How do they differ from each other in the way they behave with litmus solution?
2.What are indicators? Name three natural indicators and state the colour change each shows in acidic and basic solutions.
3.A student tests a colourless liquid with moist litmus paper and observes no change in colour. What can be concluded about the nature of the liquid? Is this test sufficient to confirm the conclusion? Explain.
4.State the colour of the following in acidic and basic solutions:
- Methyl orange
- Phenolphthalein
- Red litmus
- Turmeric
5.Why does dry hydrochloric acid gas not change the colour of dry litmus paper, but moist hydrochloric acid gas turns it red? What does this experiment prove about the nature of acids?
6.How will you test a given solution to find out whether it is acidic, basic, or neutral using: (a) litmus paper, (b) methyl orange, (c) phenolphthalein?
7.Why is a solution of sodium hydroxide slippery to touch and soapy in feel? What chemical property of bases is responsible for this?
8.State the physical properties of acids — taste, touch, and corrosive nature — and explain why acids should never be tasted directly.
9.Explain why olfactory indicators are sometimes more useful than colour-changing indicators. Give one example of an olfactory indicator and describe how it works.
10.A student adds a few drops of phenolphthalein to an acidic solution. No change is observed. She then adds a base slowly until the solution turns light pink. What change in the nature of the solution occurred? Write the name of this type of reaction.
11.What gas is produced when dilute sulphuric acid reacts with zinc granules? How will you test this gas? Write the balanced chemical equation for the reaction.
12.Write balanced chemical equations for the reaction of dilute hydrochloric acid with:
- Magnesium ribbon
- Aluminium powder
- Iron filings
13.When a metal carbonate reacts with an acid, what are the products formed? Write the balanced equation for the reaction of sodium carbonate with dilute hydrochloric acid. How is the gas produced identified?
14.What happens when dilute sulphuric acid reacts with sodium hydrogen carbonate? Write the balanced equation and identify the products.
15.State two differences between the reaction of a metal oxide with an acid and the reaction of a metal oxide with a base. Give one example of each.
16.Write the equation for the reaction of copper oxide with dilute hydrochloric acid. What change in colour is observed and why?
17.What is a neutralisation reaction? Write a balanced equation showing the neutralisation of sodium hydroxide with dilute sulphuric acid. Is the reaction exothermic or endothermic?
18.Write the balanced equations for the reactions of sodium hydroxide with:
- Dilute hydrochloric acid
- Aluminium metal
- Zinc oxide
19.Non-metallic oxides are generally acidic in nature. Explain this with the example of the reaction of sulphur dioxide with water and carbon dioxide with water.
20.What happens when excess carbon dioxide is passed into lime water that has turned milky? Write balanced equations for both the reactions involved.
21.Write the balanced equations for the following reactions:
- $\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow$
- $\text{NaOH} + \text{HCl} \rightarrow$
- $\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow$
- $\text{Na}_2\text{CO}_3 + \text{HCl} \rightarrow$
22.Explain why: (a) An aqueous solution of an acid conducts electricity, (b) A solution of glucose does not conduct electricity even though it contains hydrogen atoms.
23.What is the pH scale? What is the pH range for: (a) a strong acid, (b) a neutral solution, (c) a strong base?
24.A solution has a pH of 3 and another has a pH of 11. Which one is acidic? Which is basic? Which is more acidic — a solution of pH 2 or pH 5? Justify your answer.
25.State the importance of pH in our daily life by giving any three examples where the control of pH is essential.
26.Our stomach produces hydrochloric acid. Explain how this acid helps in digestion and what happens when excess acid is produced. What remedy is commonly used and why?
27.Explain why the pH of rainwater decreases when it passes through an atmosphere containing sulphur dioxide and nitrogen dioxide gases. What is this phenomenon called?
28.Plants grow best when the soil pH is between 6 and 7. A farmer notices that his soil is too acidic. What should he add to the soil to improve the pH? Explain the chemistry involved.
29.When a tooth decays, acids are produced in the mouth. What is the recommended remedy? Explain how toothpastes help prevent tooth decay using the concept of pH.
30.What is a universal indicator? How is it different from a single indicator like litmus? How does it help in measuring the pH of a solution?
31.How are salts formed? Classify the following salts as acidic, basic, or neutral and give reasons: (a) $\text{NaCl}$, (b) $\text{Na}_2\text{CO}_3$, (c) $\text{NH}_4\text{Cl}$, (d) $\text{CH}_3\text{COONa}$.
32.What is the pH of a salt formed from a strong acid and a strong base? Justify your answer with an example.
33.What happens when sodium chloride is heated with concentrated sulphuric acid? Write the balanced chemical equation and identify the products.
34.Explain with balanced equations how sodium hydroxide ($\text{NaOH}$) is manufactured by the chlor-alkali process. Name all the products of this process and state their important uses.
35.State three important uses each of: (a) Sodium hydroxide, (b) Hydrochloric acid, (c) Sulphuric acid.
36.Write the chemical formula of washing soda and explain how it is prepared from baking soda. Write the balanced equations involved in the preparation.
37.Write the chemical name, formula, and one important use of each of the following:
- Baking soda
- Washing soda
- Bleaching powder
- Plaster of Paris
38.What is water of crystallisation? Give the full IUPAC name and formula of blue vitriol. What happens when blue vitriol is heated?
39.Explain what happens chemically when Plaster of Paris is mixed with water. Write the equation. Why should Plaster of Paris be stored in moisture-proof containers?
40.How is bleaching powder prepared? Write its chemical formula. State any two uses of bleaching powder. Write the equation for the reaction of bleaching powder with excess carbon dioxide.
41.Explain the common salt (NaCl) family. How many molecules of water of crystallisation are present in: (a) $\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$, (b) $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$, (c) $\text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O}$?
42.A student dissolves washing soda in water and tests the solution. What colour will the solution turn with (a) red litmus paper, (b) phenolphthalein? Explain why the solution is basic in nature.
43.Write the chemical equation for the reaction used to produce sodium carbonate on a large industrial scale (Solvay process is NOT in syllabus — focus on preparation from $\text{NaHCO}_3$). How does $\text{Na}_2\text{CO}_3$ differ from $\text{NaHCO}_3$ in terms of basicity?
44.Why is baking soda used in making bread and cakes? Write the equation for its thermal decomposition and explain what role the carbon dioxide plays.
45.A milkman adds a very small amount of baking soda to fresh milk. (a) Why does he do so? (b) How does it affect the quality of the milk? (c) What will happen if excess baking soda is added?
46.What is the chemical name and formula of common salt? Describe the electrolysis of brine (concentrated sodium chloride solution) and write the products formed at the anode and cathode.
47.Explain how hydrochloric acid is obtained as a by-product from the chlor-alkali process. Write the equation for its formation and state two uses of hydrochloric acid.
48.State what happens when:
- Baking soda is heated.
- Washing soda is dissolved in water.
- Plaster of Paris sets hard after mixing with water.
Write balanced equations for each.
Ravi often suffers from acidity. His doctor tells him that his stomach produces excess hydrochloric acid ($\text{HCl}$), which irritates the stomach lining. The doctor prescribes an antacid tablet containing magnesium hydroxide ($\text{Mg(OH)}_2$), commonly called "milk of magnesia".
49.Based on Case Study 1, answer the following:
- Write the balanced equation for the reaction of $\text{Mg(OH)}_2$ with excess $\text{HCl}$.
- Why are antacids basic in nature? What is the general principle behind their action?
- Why should antacids not be taken in excess? What type of problem would excess antacid cause?
A farmer in Bihar found that her wheat crop was not growing well. A soil test revealed the soil was too acidic (pH = 4). The agriculture officer suggested treating the soil with quicklime ($\text{CaO}$).
50.Based on Case Study 2, answer the following:
- Why is an acidic soil harmful for the wheat crop?
- Write the equation for the reaction of quicklime with water and explain how slaked lime helps the soil.
- Would adding more quicklime always be beneficial? Explain with reference to pH.
A swimming pool caretaker regularly tests the pH of pool water and adds chemicals to maintain a pH between 7.2 and 7.8. She uses bleaching powder to disinfect the water.
51.Based on Case Study 3, answer the following:
- What is the active disinfectant component released by bleaching powder in water? Write the equation.
- Why is it important to maintain pH between 7.2–7.8 in the pool? What would happen at pH below 7?
- Why is bleaching powder not suitable for long-term storage?
Scientists observed that lakes in a particular region were turning acidic due to acid rain caused by industrial pollution. Aquatic life was dying and marble statues were being corroded.
52.Based on Case Study 4, answer the following:
- Name the two main gases responsible for acid rain and write equations showing how they form acid rain.
- Write the chemical equation showing how marble ($\text{CaCO}_3$) is corroded by acid rain.
- Suggest two methods to prevent acid rain.
After a fracture, a doctor applied Plaster of Paris (POP) to Ankit's leg. The doctor warned him not to get the plaster wet. Within 30 minutes, the plaster hardened completely.
53.Based on Case Study 5, answer the following:
- Write the chemical name and formula of Plaster of Paris. Write the equation for its setting reaction.
- Why does the plaster expand slightly when it sets? Why is this property useful for fractures?
- Explain why Plaster of Paris should not be exposed to moisture during storage.
Arun drops an effervescent vitamin C tablet into a glass of water. The tablet fizzes vigorously and dissolves completely. The resulting solution turns blue litmus red.
54.Based on the above observation, answer the following:
- What does the fizzing indicate? Name the gas likely produced.
- What does the colour change of blue litmus to red indicate about the final solution?
- Name a common ingredient in effervescent tablets that reacts with the acid to produce the fizz. Write the reaction.
A white crystalline substance 'X' turns moist litmus paper blue. When heated, it decomposes to give a gas 'Y' that turns lime water milky, a white solid 'Z', and water vapour. When dissolved in water, the solution is found to be alkaline in nature.
55.Based on the description above, answer the following:
- Identify substance 'X', gas 'Y', and solid 'Z'.
- Write the balanced chemical equation for the thermal decomposition of 'X'.
- State two important uses of substance 'X'.
56.Arrange the following solutions in increasing order of their hydrogen ion ($\text{H}^+$) concentration: Lemon juice (pH = 2.5), Blood (pH = 7.4), Baking soda solution (pH = 8.3), Gastric juice (pH = 1.2), Pure water (pH = 7).
57.A student adds a few drops of universal indicator to five test tubes containing: (1) vinegar, (2) ammonia solution, (3) distilled water, (4) sodium hydroxide solution, (5) orange juice. Predict the approximate colour of the indicator in each test tube.
58.Iron pipes are coated with zinc to prevent rusting. At the same time, factories manufacturing paper use sodium hydroxide. Explain:
- Why does zinc protect iron better than paint?
- In what step of paper manufacturing is NaOH used?
59.Why does an electric current pass through an aqueous solution of acids but not through pure acids? What type of ions are produced by acids in water? Explain with an example.
60.State the differences between strong acids and weak acids with one example each. Which one completely ionises in water?
61.Explain what happens when carbon dioxide is passed through sodium hydroxide solution. Write the balanced equation. If CO2 is passed in excess, what change occurs? Write the equation for the second reaction.
62.Write the complete balanced equations for: (a) Preparation of $\text{NaHCO}_3$ from $\text{Na}_2\text{CO}_3$. (b) Conversion of $\text{NaHCO}_3$ to $\text{Na}_2\text{CO}_3$. State the conditions required.
63.A solution of $\text{HCl}$ in organic solvent benzene does not conduct electricity, but a solution of $\text{HCl}$ in water does. Explain this difference in terms of ionisation and ion formation.
64.State which of the following are acidic, basic, or neutral oxides: (a) $\text{SO}_2$, (b) $\text{Na}_2\text{O}$, (c) $\text{CO}$, (d) $\text{CaO}$, (e) $\text{NO}_2$. Write equations for the reaction of each acidic oxide with water.
65.An old woman complains of joint pain. Her doctor tells her she has gout, caused by excess uric acid deposits in her joints. A neighbour suggests drinking dilute baking soda solution daily. Using your knowledge of acids and bases, evaluate whether this suggestion is chemically reasonable. What are the risks of excess consumption?
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