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Q1. The word ‘acid’ comes from the Latin word ‘acidus’. What is the meaning of ‘acidus’?
The word ‘acid’ comes from the Latin word ‘acidus’, which means sour. Acids are substances that have a sour taste. For example, lemon juice and vinegar are acidic and taste sour.
Q2. Which of the following is a natural acid found in curd?
Lactic acid is found in curd. It is produced by the fermentation of milk sugar (lactose) by bacteria. This acid gives curd its sour taste. Citric acid is found in citrus fruits, tartaric acid in tamarind, and acetic acid in vinegar.
Q3. Vinegar is a common substance in our kitchens. Which acid is present in it?
Vinegar contains acetic acid. It is a weak acid that gives vinegar its sour taste and pungent smell. Citric acid is in lemons, tartaric acid is in tamarind, and oxalic acid is in tomatoes.
Q4. Lemons and oranges taste sour because they contain a specific acid. What is it?
Lemons and oranges contain citric acid, which gives them their sour taste. Lactic acid is in curd, tartaric acid is in tamarind, and ascorbic acid is Vitamin C. Citric acid is the main acid in citrus fruits.
Q5. Tamarind is used as a souring agent in many Indian dishes. Which acid gives it this sour taste?
Tamarind contains tartaric acid, which gives it its sour taste. Citric acid is in citrus fruits, lactic acid is in curd, and acetic acid is in vinegar. Tartaric acid is the specific acid in tamarind.
Q6. What is the general name for acids that are obtained from natural sources like plants and animals?
Acids obtained from natural sources like plants and animals are called organic acids. Examples include citric acid, lactic acid, and acetic acid. Mineral acids are obtained from minerals, and strong acids are a subcategory of mineral acids. Organic acids are generally weak.
Q7. Acids that are prepared from minerals of the earth are called mineral acids. Which of these is a mineral acid?
Sulphuric acid is a mineral acid prepared from minerals. Citric acid, lactic acid, and acetic acid are organic acids obtained from natural sources. Mineral acids are typically strong and corrosive.
Q8. Which acid is known as the ‘Queen of Chemicals’?
Nitric acid is known as the ‘Queen of Chemicals’. It is a powerful mineral acid used in the manufacturing of fertilizers and explosives. Sulphuric acid is known as the ‘King of Chemicals’.
Q9. Nitric acid is another important mineral acid. In which of the following processes is it commonly used?
Nitric acid is commonly used in the manufacturing of fertilizers like ammonium nitrate. It is also used in the production of explosives. Soaps are made using bases like sodium hydroxide, and window cleaners contain ammonium hydroxide.
Q10. Our stomach produces a mineral acid to help digest food. Which acid is this?
Our stomach produces hydrochloric acid (HCl) to help digest food and kill bacteria. Sulphuric acid, nitric acid, and phosphoric acid are not produced by the stomach. HCl is essential for the digestion process.
Q11. Phosphoric acid is often used to add a tangy flavor to soft drinks. What is its chemical formula?
The chemical formula of phosphoric acid is H₃PO₄. HCl is hydrochloric acid, H₂SO₄ is sulphuric acid, and HNO₃ is nitric acid. Phosphoric acid is commonly used in soft drinks to add a tangy flavour.
Q12. Which type of acids are the building blocks of fats and oils?
Fats and oils are made up of fatty acids and glycerol. Amino acids are the building blocks of proteins, nucleic acids form DNA and RNA, and mineral acids are not building blocks of biological molecules. Fatty acids are essential components of lipids.
Q13. Proteins are made up of smaller units. What are these units called?
Proteins are made up of smaller units called amino acids. Fatty acids are components of fats, nucleic acids form DNA and RNA, and sulphuric acid is a mineral acid. Amino acids are the building blocks of proteins.
Q14. The molecule that carries our genetic information is called DNA. What type of acid is DNA?
DNA (deoxyribonucleic acid) is a nucleic acid. It carries genetic information in living organisms. Fatty acids are for fats, amino acids are for proteins, and mineral acids are inorganic. Nucleic acids are the correct type for DNA.
Q15. Soap is a common substance we use for bathing. What is the nature of a soap solution?
Soap solution is basic in nature. It turns red litmus paper blue and feels soapy to the touch. Acids are sour, and neutral substances do not change litmus color. Soap is a base and has a bitter taste and slippery feel.
Q16. Liquid soap often contains a base that is also found in window cleaners. Which base is this?
Sodium hydroxide (NaOH) is used in both liquid soaps and window cleaners. Calcium hydroxide is used in whitewashing, magnesium hydroxide is in Milk of Magnesia, and potassium hydroxide is used in some soaps but not commonly in window cleaners. NaOH is the correct answer.
Q17. A white solid is used for whitewashing walls. When mixed with water, it forms limewater. What is this substance?
Calcium hydroxide, also known as slaked lime or lime, is used for whitewashing walls. Its solution is called limewater. Sodium hydroxide is caustic soda, magnesium hydroxide is Milk of Magnesia, and ammonium hydroxide is a cleaning agent.
Q18. Doctors prescribe ‘Milk of Magnesia’ to relieve acidity or indigestion. What is its chemical name?
Milk of Magnesia is magnesium hydroxide, Mg(OH)₂. It is a base used to neutralize excess stomach acid. Calcium hydroxide is lime, sodium hydroxide is caustic soda, and ammonium hydroxide is a cleaning agent.
Q19. A base is used in the manufacturing of soaps and is a key ingredient in drain cleaners. Its chemical formula is NaOH. What is its common name?
Sodium hydroxide (NaOH) is commonly known as caustic soda. It is used in soap making and as a drain cleaner. Potassium hydroxide is KOH, calcium hydroxide is Ca(OH)₂, and ammonium hydroxide is NH₄OH.
Q20. Many window cleaning solutions contain a base with the formula NH₄OH. What is its chemical name?
Ammonium hydroxide (NH₄OH) is used in window cleaning solutions. Sodium hydroxide is NaOH, calcium hydroxide is Ca(OH)₂, and magnesium hydroxide is Mg(OH)₂. NH₄OH is the correct formula for ammonium hydroxide.
Q21. What is the general name for a substance, like litmus or turmeric, that changes color to show whether a solution is acidic or basic?
An indicator is a substance that changes color in acidic or basic solutions. Litmus and turmeric are natural indicators. A catalyst speeds up a reaction, a reagent is a substance used in a chemical reaction, and a solvent dissolves substances.
Q22. Litmus is a natural dye extracted from a plant. What is its original color?
Litmus is a natural dye extracted from lichens. Its original color is purple. It turns red in acidic solutions and blue in basic solutions. Red and blue litmus papers are prepared by treating the purple dye with acids and bases.
Q23. A student adds a drop of a liquid to a red litmus paper. The paper turns blue. What is the nature of the liquid?
Red litmus paper turns blue in a basic solution. Acids turn blue litmus red. A neutral solution does not change the color of either red or blue litmus. The liquid is basic because it turned red litmus blue.
Q24. A student adds a drop of a liquid to a blue litmus paper. The paper turns red. What is the nature of the liquid?
Blue litmus paper turns red in an acidic solution. Basic solutions turn red litmus blue. Neutral solutions do not change litmus color. The liquid is acidic because it turned blue litmus red.
Q25. A solution is tested with both red and blue litmus papers, and neither paper changes color. What is the solution?
A neutral solution does not change the color of either red or blue litmus paper. Acids turn blue litmus red, and bases turn red litmus blue. Since neither paper changes, the solution is neutral.
Q26. Soap solution turns the color of ______ litmus paper to blue.
Soap solution is basic. It turns red litmus paper blue. Blue litmus paper remains blue in a basic solution. Green and yellow litmus are not standard indicators. The correct answer is red litmus.
Q27. What effect does lemon juice, an acid, have on blue litmus paper?
Lemon juice is acidic. Acids turn blue litmus paper red. Bases turn red litmus blue. Neutral substances do not change litmus color. Lemon juice will turn blue litmus red.
Q28. Turmeric is a natural indicator used in Indian kitchens. Its paste is yellow. What color does it turn when a basic solution like soap is added to it?
Turmeric is yellow in acidic or neutral solutions. When a basic solution like soap is added to turmeric, it turns reddish-brown. The options given include red, which is the closest. Turmeric paper turns reddish-brown in bases.
Q29. A woman’s white saree gets a yellow stain of turmeric during a festival. Later, while washing, her soapy hands accidentally rub the stain. What will happen to the stain?
Turmeric is a natural indicator. The yellow stain will turn reddish-brown (darker red) when it comes in contact with soap, which is basic. This happens because turmeric changes color in basic solutions.
Q30. China rose is an indicator. Its solution is generally ______ in color.
China rose solution is generally light pink or magenta in color. It is a natural indicator extracted from the petals of the China rose flower. It turns green in basic solutions and dark pink or magenta in acidic solutions.
Q31. When an acid is added to a China rose indicator, what color change is observed?
China rose indicator turns dark pink or magenta in acidic solutions. It turns green in basic solutions. The original color is light pink. Acids cause the color to become darker pink.
Q32. When a base is added to a China rose indicator, what color change is observed?
China rose indicator turns green in basic solutions. It turns dark pink or magenta in acidic solutions. The original color is light pink. Bases cause the color to change to green.
Q33. You have a China rose indicator (magenta color). You add it to a sample of tap water and the color changes to green. What does this tell you about the tap water?
China rose indicator turns green in basic solutions. Since the magenta indicator turned green, the tap water must be basic. It would remain magenta or turn dark pink in acidic solutions, and stay the same in neutral solutions.
Q34. Which of the following is NOT a natural indicator?
Phenolphthalein is a synthetic indicator, not a natural one. Litmus, turmeric, and China rose are all natural indicators. Phenolphthalein is commonly used in acid-base titrations in laboratories.
Q35. A substance tastes sour and turns blue litmus red. It is likely to be ______.
Lemon juice is acidic, tastes sour, and turns blue litmus red. Soap and baking soda are basic, and water is neutral. Acids have a sour taste and turn blue litmus red.
Q36. A substance feels soapy to touch and turns red litmus blue. It is likely to be ______.
Soap solution is basic, feels soapy, and turns red litmus blue. Vinegar, orange juice, and lemon juice are acidic and taste sour. Bases are slippery to touch and turn red litmus blue.
Q37. What is the nature of a substance that does not change the color of either red or blue litmus paper?
A neutral substance does not change the color of either red or blue litmus paper. Acids turn blue litmus red, and bases turn red litmus blue. Neutral substances like water do not affect litmus paper.
Q38. Which of the following eatable substances contains oxalic acid?
Spinach contains oxalic acid. Lemon contains citric acid, vinegar contains acetic acid, and tomatoes contain oxalic acid as well (but spinach is the classic example). Oxalic acid is also found in tomatoes and some other vegetables.
Q39. What type of acid is ascorbic acid, which is commonly known as Vitamin C?
Ascorbic acid (Vitamin C) is an organic acid. It is found naturally in fruits and vegetables. Mineral acids are inorganic, strong acids are a category of mineral acids, and fatty acids are components of fats. Organic acids are derived from living organisms.
Q40. The image shows a bottle of a soft drink. Which acid, besides carbonic acid, is commonly found in these drinks to give them a tangy flavor?
Phosphoric acid is commonly added to soft drinks to give them a tangy flavor. Lactic acid is in curd, tartaric acid is in tamarind, and acetic acid is in vinegar. Phosphoric acid is used in cola drinks.
Q41. A gardener wants to reduce the acidity of his garden soil. Which substance should he add?
Lime (calcium hydroxide) is a base that neutralizes acidic soil, reducing its acidity. Vinegar and lemon juice are acids and would increase acidity, and water would not neutralize acidity effectively. Lime is commonly used to treat acidic soil.
Q42. An ant sting injects methanoic acid into the skin. What natural remedy can be used to neutralize it?
Baking soda (sodium bicarbonate) is a base that neutralizes the methanoic acid from an ant sting. Vinegar and lemon juice are acids and would worsen the sting. Water would not neutralize the acid. Baking soda is a common remedy for ant and bee stings.
Q43. Why is it dangerous to mix acids with bases directly?
Mixing acids with bases directly produces a large amount of heat (exothermic reaction), which can be dangerous and cause burns. This is why they should be mixed slowly and carefully, especially in laboratories. The heat generated can be hazardous.
Q44. A beaker contains a colorless liquid. A drop of it on a turmeric paper turns it reddish-brown. What is the nature of the liquid?
Turmeric paper turns reddish-brown in basic solutions. Acids do not change turmeric color (it remains yellow), and neutral substances also do not change it. The liquid is basic because it turned turmeric paper reddish-brown.
Q45. Which base is commonly known as ‘caustic soda’ and has the chemical formula NaOH?
Sodium hydroxide (NaOH) is commonly known as caustic soda. Potassium hydroxide is KOH, calcium hydroxide is Ca(OH)₂, and magnesium hydroxide is Mg(OH)₂. Caustic soda is a strong base used in soap making and drain cleaners.
Q46. Which acid is known as the ‘King of Chemicals’ and is used in car batteries?
Sulphuric acid (H₂SO₄) is known as the ‘King of Chemicals’. It is used in car batteries (lead-acid batteries). Hydrochloric acid is HCl, nitric acid is HNO₃, and phosphoric acid is H₃PO₄. Sulphuric acid is the most widely used industrial chemical.
Q47. What is the chemical name and formula for the base found in ‘Milk of Magnesia’?
Milk of Magnesia is magnesium hydroxide (Mg(OH)₂). Sodium hydroxide is NaOH, calcium hydroxide is Ca(OH)₂, and ammonium hydroxide is NH₄OH. Magnesium hydroxide is used as an antacid to neutralize stomach acid.
Q48. Which base is used in the process of whitewashing walls and its solution is known as limewater?
Calcium hydroxide (Ca(OH)₂) is used for whitewashing walls, and its solution is called limewater. Sodium hydroxide is caustic soda, potassium hydroxide is potash, and ammonium hydroxide is a cleaning agent. Calcium hydroxide is the base used in whitewashing.
Q49. Acids react with metals to produce a gas. Which gas is produced?
Acids react with metals to produce hydrogen gas. For example, zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas. Oxygen, nitrogen, and carbon dioxide are not produced in this reaction. Hydrogen is the correct gas.
Q50. If a liquid has a pH of 7, what is its nature?
A pH of 7 is neutral. Acids have pH less than 7, and bases have pH greater than 7. A pH of 7 indicates a neutral substance like pure water. It is neither acidic nor basic.