Practice Questions | Fill in the Blanks | Multiple Choice Questions (MCQs) | Board Examination Questions
1. What are acids? Give three examples of acids found in everyday life.
Acids are substances that donate protons (H+ ions) when dissolved in water. Three examples of acids found in everyday life are: 1) Citric acid in lemons and oranges, 2) Acetic acid in vinegar, and 3) Hydrochloric acid in our stomach.
2. Define bases and give three examples of bases used in daily life.
Bases are substances that accept protons (H+ ions) or donate hydroxide (OH-) ions when dissolved in water. Three examples of bases used in daily life are: 1) Sodium hydroxide in drain cleaners, 2) Magnesium hydroxide in milk of magnesia, and 3) Ammonium hydroxide in household cleaners.
3. What is the pH scale? Explain its significance.
The pH scale is a measure of the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic. It’s significant because it helps in determining the nature and strength of solutions, which is crucial in various fields like chemistry, biology, and environmental science.
4. What are salts? Explain their formation.
Salts are ionic compounds formed by the reaction of an acid with a base, resulting in the neutralization of their respective properties. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), sodium chloride (common salt) and water are formed.
5. What is the difference between strong acids and weak acids?
Strong acids completely dissociate in water to produce H+ ions, resulting in a low pH. Examples include hydrochloric acid and sulfuric acid. Weak acids only partially dissociate, maintaining a higher pH. Examples include acetic acid and citric acid.
6. Explain the neutralization reaction with an example.
A neutralization reaction is when an acid reacts with a base to produce salt and water. For example, when sulfuric acid (H2SO4) reacts with sodium hydroxide (NaOH), it forms sodium sulfate (Na2SO4) and water (H2O). The reaction is: H2SO4 + 2NaOH → Na2SO4 + 2H2O.
7. What is an indicator? Give examples.
Indicators are substances that change color when in contact with acids or bases, helping to identify their nature. Common examples include litmus paper (red in acid, blue in base) and phenolphthalein (colorless in acid, pink in base).
8. Describe the effect of acids on metals.
Acids react with certain metals to produce hydrogen gas and a salt. For example, when hydrochloric acid reacts with zinc, zinc chloride and hydrogen gas are produced. This reaction can be represented as: Zn + 2HCl → ZnCl2 + H2↑.
9. Explain the term ‘alkali’ and provide examples.
An alkali is a subset of bases that are soluble in water, yielding hydroxide ions (OH-) when dissolved. Examples include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2).
10. Discuss the properties of acids.
Acids have several characteristic properties: they taste sour, turn blue litmus paper red, can conduct electricity when dissolved, and produce H+ ions in solution. They also react with bases to form salts and water in neutralization reactions.
11. Describe how to prepare a solution of hydrochloric acid.
Hydrochloric acid is prepared by dissolving hydrogen chloride gas in water. In a laboratory setting, it’s crucial to add the acid to water (not water to acid) to avoid splattering. The concentration can be adjusted by controlling the amount of HCl gas dissolved.
12. What is the role of water in acid-base reactions?
Water plays a crucial role in acid-base reactions as it acts as a medium for the dissociation of acids and bases. It allows for the formation of hydronium (H3O+) ions from acids and hydroxide (OH-) ions from bases. Water also participates in autoionization, maintaining a balance of H+ and OH- ions.
13. Explain the concept of acid rain and its effects.
Acid rain is precipitation with high levels of nitric and sulfuric acids, formed when sulfur dioxide and nitrogen oxides react with water in the atmosphere. It can harm plants, aquatic life, and buildings by increasing the acidity of soil and water bodies, and corroding structures.
14. What are amphoteric substances? Give examples.
Amphoteric substances can act as both acids and bases depending on the other reactant. Examples include water (H2O), aluminum hydroxide (Al(OH)3), and zinc hydroxide (Zn(OH)2). These substances can donate or accept protons based on the reaction conditions.
15. Describe the process of soap making.
Soap making involves the saponification process, where fats or oils (triglycerides) react with a strong base like sodium hydroxide (lye) to produce soap (sodium salt of fatty acids) and glycerol. This is an example of base hydrolysis of esters.
16. What is a buffer solution? How does it work?
A buffer solution resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). Buffers work by neutralizing small amounts of added acid or base, maintaining a relatively stable pH.
17. Explain the concept of acid-base titration.
Acid-base titration is a method to determine the concentration of an acid or base by precisely neutralizing it with a standard solution of known concentration. An indicator is used to determine the endpoint of the reaction, where the amounts of acid and base are stoichiometrically equivalent.
18. What are Lewis acids and bases?
Lewis acids are electron pair acceptors, while Lewis bases are electron pair donors. This definition broadens the concept of acids and bases beyond proton transfer. For example, boron trifluoride (BF3) is a Lewis acid as it can accept an electron pair, while ammonia (NH3) is a Lewis base as it can donate an electron pair.
19. Describe the industrial uses of acids and bases.
Acids and bases have numerous industrial applications. Sulfuric acid is used in fertilizer production and car batteries. Hydrochloric acid is used in steel processing and cleaning. Sodium hydroxide is used in paper production and soap making. Calcium hydroxide is used in water treatment and construction.
20. What is the importance of pH in biological systems?
pH is crucial in biological systems as it affects enzyme activity, protein structure, and cellular processes. Blood pH must be maintained within a narrow range (7.35-7.45) for proper functioning. Stomach acid (pH ~2) aids in digestion and kills harmful bacteria. Plant growth is influenced by soil pH, affecting nutrient availability.
1. The pH of a neutral solution is ______.
Answer: 7
2. Acids turn blue litmus paper ______.
Answer: red
3. The process of dissolving an acid or base in water is called ______.
Answer: dissociation
4. A substance that changes color in acidic or basic solutions is called an ______.
Answer: indicator
5. The reaction between an acid and a base to produce salt and water is called ______.
Answer: neutralization
6. Bases that are soluble in water are called ______.
Answer: alkalis
7. The pH of blood in a healthy human body ranges from ______ to ______.
Answer: 7.35 to 7.45
8. ______ is an example of a weak acid found in vinegar.
Answer: Acetic acid
9. The universal indicator turns ______ in strongly acidic solutions and ______ in strongly basic solutions.
Answer: red, purple
10. The common name for sodium bicarbonate is ______.
Answer: baking soda
1. Which of the following is not an acid?
a) HCl
b) H2SO4
c) NaOH
d) CH3COOH
Answer: c) NaOH (sodium hydroxide is a base)
2. Which of the following salts will form an acidic solution when dissolved in water?
a) NaCl
b) KNO3
c) NH4Cl
d) Na2CO3
Answer: c) NH4Cl (ammonium chloride hydrolyzes to form an acidic solution)
3. Which of the following is not a characteristic of bases?
a) Bitter taste
b) Slippery feel
c) Turn red litmus blue
d) React with metals to produce hydrogen gas
Answer: d) React with metals to produce hydrogen gas (this is a characteristic of acids, not bases)
4. What is the chemical formula of Plaster of Paris (POP)?
a) CaSO4·2H2O
b) CaSO4·½H2O
c) Ca(OH)2
d) CaCO3
Answer: b) CaSO4·½H2O (Calcium sulfate hemihydrate)
5. What is the main component of bleaching powder?
a) Sodium hypochlorite
b) Calcium hypochlorite
c) Potassium permanganate
d) Hydrogen peroxide
Answer: b) Calcium hypochlorite
6. Which of the following is NOT a use of baking soda?
a) As an antacid
b) In fire extinguishers
c) As a bleaching agent
d) In baking as a leavening agent
Answer: c) As a bleaching agent (this is a function of bleaching powder, not baking soda)
7. What is the chemical formula of washing soda?
a) Na2CO3
b) Na2CO3·10H2O
c) NaHCO3
d) NaOH
Answer: b) Na2CO3·10H2O (Sodium carbonate decahydrate)
8. What is water of crystallisation?
a) Water used to dissolve crystals
b) Water chemically combined in a definite ratio in crystals
c) Water produced during crystal formation
d) Water used to clean crystals
Answer: b) Water chemically combined in a definite ratio in crystals
9. Which of the following is a use of Plaster of Paris?
a) As a food preservative
b) In the manufacture of cement
c) In making surgical casts for broken bones
d) As a cleaning agent
Answer: c) In making surgical casts for broken bones
10. What happens when Plaster of Paris is mixed with water?
a) It dissolves completely
b) It forms a hard mass
c) It produces hydrogen gas
d) It turns into powder
Answer: b) It forms a hard mass
11. Which of the following is a use of bleaching powder?
a) As a leavening agent in baking
b) As an antacid
c) For disinfecting drinking water
d) As a food preservative
Answer: c) For disinfecting drinking water
12. What is the chemical name of baking soda?
a) Sodium carbonate
b) Sodium bicarbonate
c) Sodium hydroxide
d) Sodium chloride
Answer: b) Sodium bicarbonate
13. What is the use of washing soda?
a) As a food additive
b) In the manufacture of glass
c) As a medical antiseptic
d) In baking cakes
Answer: b) In the manufacture of glass
14. Which of the following statements about water of crystallisation is false?
a) It is the fixed number of water molecules present in one formula unit of a salt
b) It can be removed by heating the salt
c) It always increases the solubility of the salt
d) It can affect the color of some salts
Answer: c) It always increases the solubility of the salt (this is not always true; it depends on the specific salt)
15. What happens when washing soda (Na2CO3·10H2O) is exposed to air?
a) It gains water molecules
b) It loses water molecules
c) It remains unchanged
d) It reacts with nitrogen in the air
Answer: b) It loses water molecules (washing soda is efflorescent and loses water when exposed to air)
1. What happens when a solution of an acid is mixed with a solution of a base in a test tube?
Answer: When a solution of an acid is mixed with a solution of a base in a test tube, a neutralization reaction occurs. This reaction produces salt and water, and is often accompanied by the evolution of heat.
2. How is the concentration of hydronium (H3O+) ions affected when an acid is diluted?
Answer: When an acid is diluted, the concentration of hydronium (H3O+) ions decreases. This is because adding water increases the volume of the solution while the number of H3O+ ions remains constant, resulting in a lower concentration.
3. Write a balanced chemical equation for the reaction between sodium hydroxide and hydrochloric acid.
Answer: The balanced chemical equation for the reaction between sodium hydroxide and hydrochloric acid is: NaOH + HCl → NaCl + H2O
4. What is the effect of adding a few drops of a universal indicator to distilled water?
Answer: When a few drops of a universal indicator are added to distilled water, the color of the solution will typically turn green. This is because distilled water is neutral (pH 7), and universal indicators usually show green for neutral solutions.
5. Explain why aqueous solutions of acids conduct electricity.
Answer: Aqueous solutions of acids conduct electricity because acids dissociate in water to produce ions. These ions (H+ and the anion of the acid) are mobile charge carriers that can move through the solution, allowing for the conduction of electricity.
6. What is the role of water in the Arrhenius concept of acids and bases?
Answer: In the Arrhenius concept, water plays a crucial role as the solvent. According to this theory, acids are substances that produce H+ ions (protons) when dissolved in water, while bases are substances that produce OH- ions (hydroxide ions) when dissolved in water.
7. Describe the process of preparation of washing soda from baking soda.
Answer: Washing soda (Na2CO3) is prepared from baking soda (NaHCO3) through the following steps: 1. Baking soda is heated: 2NaHCO3 → Na2CO3 + H2O + CO2 2. The resulting sodium carbonate is dissolved in water and recrystallized to form washing soda: Na2CO3 + 10H2O → Na2CO3·10H2O
8. What is the difference between the chemical formula of quick lime and slaked lime?
Answer: Quick lime is calcium oxide (CaO), while slaked lime is calcium hydroxide (Ca(OH)2). Slaked lime is formed when quick lime reacts with water: CaO + H2O → Ca(OH)2
9. Write the chemical equation for the reaction that takes place when chlorine is passed through dry slaked lime.
Answer: When chlorine is passed through dry slaked lime, bleaching powder is formed. The reaction can be represented as: Ca(OH)2 + Cl2 → CaOCl2 + H2O
10. Explain why a solution of plaster of Paris should be used quickly after it is mixed with water.
Answer: A solution of plaster of Paris should be used quickly after mixing with water because it undergoes a setting reaction. When water is added to plaster of Paris (CaSO4·½H2O), it forms gypsum (CaSO4·2H2O), which hardens rapidly. If not used quickly, the mixture will set and become unusable.