📘 Welcome
Hi User, you have selected Read Mode.
This is Time Free Mode for your convenience to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main page designed especially with Exam Features.
This is Time Free Mode for your convenience to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main page designed especially with Exam Features.
Q1. Phenolphthalein is a synthetic indicator. What color does it turn when added to a basic solution like sodium hydroxide?
Phenolphthalein is a synthetic indicator that is colorless in acidic and neutral solutions but turns pink in basic solutions. The pink color appears because the indicator changes its structure in the presence of hydroxide ions (OH⁻) from the base. The other colors (yellow, red, green) are not associated with phenolphthalein in basic solutions.
Q2. A student adds a few drops of phenolphthalein to a solution of hydrochloric acid. What color change will he observe?
Phenolphthalein is colorless in acidic solutions. Hydrochloric acid is an acid, so when phenolphthalein is added to it, the solution remains colorless. It does not turn pink (which happens in bases) or red.
Q3. A student adds phenolphthalein to a colorless solution, and it turns pink. What is the nature of the solution?
Phenolphthalein turns pink only in basic solutions. If the solution turns pink, it is basic. Acids and neutral solutions do not turn phenolphthalein pink (they remain colorless). Therefore, the solution is basic.
Q4. Limewater is a basic solution. If a few drops of phenolphthalein are added to it, what will happen?
Limewater is a basic solution (calcium hydroxide). Phenolphthalein turns pink in basic solutions. Therefore, adding phenolphthalein to limewater will make it turn pink. It will not become colorless (that happens in acids), red, or blue.
Q5. Generally, acids have a specific taste. What is that taste?
Acids generally have a sour taste. For example, lemon juice (citric acid) and vinegar (acetic acid) taste sour. Bases have a bitter taste and feel soapy. Sweet and salty are not characteristics of acids.
Q6. How do dilute acids generally feel when touched? (With a warning that this should never be tested directly)
Dilute acids do not have a specific feel on the skin (though they can be corrosive). It is bases that feel soapy and slippery. Strong acids can cause burns, so they should never be touched directly. The question emphasizes the warning.
Q7. Which gas is usually produced when an acid reacts with an active metal like zinc?
When an acid reacts with an active metal like zinc, hydrogen gas is produced. For example, zinc + hydrochloric acid → zinc chloride + hydrogen gas. Oxygen, carbon dioxide, and nitrogen are not produced in this reaction.
Q8. Acid rain is an environmental problem. What is the main cause of acid rain?
Acid rain is caused by the release of sulphur dioxide (SO₂) and nitrogen oxides (NOx) into the atmosphere from burning fossil fuels like coal and oil. These gases react with water vapour to form sulphuric and nitric acids, which fall as acid rain.
Q9. What is the approximate pH of normal rain water?
Normal rain water is slightly acidic with a pH of about 5.6 due to the presence of dissolved carbon dioxide forming carbonic acid. pH below 5.6 is considered acid rain, pH 7 is neutral, and above 8 is basic.
Q10. Acid rain can cause damage to buildings made of which material?
Acid rain damages buildings made of marble and limestone because these contain calcium carbonate (CaCO₃). The acid reacts with calcium carbonate to form soluble compounds that wash away, causing corrosion. This is why historical monuments like the Taj Mahal are affected by acid rain.
Q11. What is the chemical process called when an acid and a base react to form salt and water?
The reaction between an acid and a base to form salt and water is called neutralization. This is because the acidic and basic properties neutralize each other. For example, HCl + NaOH → NaCl + H₂O.
Q12. A person suffers from indigestion due to excess acid in the stomach. What type of substance is taken to relieve this pain?
Antacids are basic substances that neutralize excess stomach acid, providing relief from indigestion and heartburn. Common antacids contain bases like magnesium hydroxide or sodium bicarbonate. Acidic or sour substances would worsen the condition.
Q13. Milk of Magnesia is often used as an antacid. Which base does it contain?
Milk of Magnesia is magnesium hydroxide (Mg(OH)₂). It is a mild base used as an antacid to neutralize stomach acid. Sodium hydroxide is too strong and corrosive, calcium hydroxide is used in whitewashing, and ammonium hydroxide is used in cleaning solutions.
Q14. Baking soda is a common home remedy for acidity. What is its chemical name?
Baking soda is sodium hydrogen carbonate (NaHCO₃). It is a weak base that neutralizes excess acid in the stomach. Sodium chloride is common salt, sodium carbonate is washing soda, and calcium carbonate is limestone.
Q15. Farmers add slaked lime to their fields. What is the purpose of this practice?
Slaked lime (calcium hydroxide) is added to acidic soil to neutralize the acidity and make the soil suitable for crop growth. This is a common agricultural practice to adjust soil pH. It does not primarily add nutrients or kill insects.
Q16. Sometimes farmers add organic matter (compost) to the soil. This can also help treat soil that is too ______.
Organic matter (compost) can help treat soil that is too basic (alkaline). It releases organic acids during decomposition, which helps neutralize the alkalinity and improve soil health. It also improves soil structure and fertility.
Q17. Waste from factories is often acidic. Why is it dangerous to dump this waste directly into rivers?
Acidic factory waste can drastically lower the pH of river water, making it acidic. This is harmful to aquatic life, as many organisms cannot survive in acidic conditions. It can also disrupt the ecosystem. Changing color, making salty, or freezing are not the primary dangers.
Q18. How is acidic factory waste treated before being released into water bodies?
Acidic factory waste is treated by adding a base (like lime or sodium hydroxide) to neutralize it. This brings the pH to a safe level before the waste is released into water bodies. Dilution alone is not effective, and boiling or filtering does not neutralize acidity.
Q19. When an ant stings a person, it injects a liquid into the skin. What is the nature of this liquid?
An ant sting injects methanoic acid (formic acid) into the skin. This acid causes the burning sensation and irritation. The liquid is acidic, not basic, neutral, or salty.
Q20. What is a common household remedy to apply on an ant sting to get relief?
Baking soda (sodium hydrogen carbonate) is a base. It neutralizes the methanoic acid injected by the ant sting, providing relief. Lemon juice and vinegar are acidic and would worsen the sting, and salt would not neutralize the acid.
Q21. A bee sting is different from an ant sting. What is the nature of the liquid injected by a bee sting?
A bee sting injects a basic (alkaline) liquid into the skin. This is opposite to an ant sting, which injects an acid. The basic nature of the bee venom causes the pain and swelling.
Q22. What can be used to treat a bee sting?
Since a bee sting is basic, it can be neutralized by applying a weak acid like lemon juice or vinegar. Baking soda paste (a base) is used for ant stings (which are acidic). Soap is basic and would not help, and sugar would have no effect.
Q23. Why is it important to know whether a sting is from an ant or a bee before applying a remedy?
An ant sting is acidic (methanoic acid) and needs a base (like baking soda) for treatment. A bee sting is basic and needs an acid (like vinegar or lemon juice) for treatment. Using the wrong treatment can worsen the condition.
Q24. In very hot weather, milk spoils quickly and becomes sour. Why does this happen?
In hot weather, bacteria grow rapidly in milk and convert lactose (milk sugar) into lactic acid. This makes the milk sour and causes it to curdle. The heat does not kill bacteria; it promotes their growth. Evaporation and fat separation are not the primary causes.
Q25. To preserve milk for a short period, especially in warm weather, people often boil it. Why does boiling help?
Boiling milk kills the bacteria that cause souring, thereby preserving it for a longer period. It does not add nutrients, make it sweeter, or remove all the water. Boiling is a simple method of pasteurization.
Q26. A student accidentally spills dilute hydrochloric acid on the laboratory floor. The teacher instructs her to neutralize it with a base. Which substance would be safest to use?
Baking soda is a mild base and safe to use for neutralizing acid spills. Concentrated sodium hydroxide is a strong base and would be dangerous. Water would dilute the acid but not neutralize it, and sulphuric acid would add more acid. Baking soda is the safest option.
Q27. What will be the products when an acid reacts with a base in a neutralization reaction?
In a neutralization reaction, an acid reacts with a base to produce salt and water. For example, HCl + NaOH → NaCl + H₂O. Carbon dioxide and hydrogen gas are not produced in a typical neutralization reaction.
Q28. Why is it not advisable to take antacid tablets regularly without a doctor’s advice?
Regular use of antacids can make the stomach too basic, interfering with normal digestion and potentially causing other health issues. It can also mask underlying conditions. Therefore, they should be taken only as advised by a doctor.
Q29. Besides using a base, how can the effects of acid rain on a lake be reduced?
Adding a basic substance like lime (calcium hydroxide) to a lake neutralizes the acidity caused by acid rain, a process called liming. This helps restore the pH balance and protect aquatic life. Adding more acid would worsen the problem, and boiling or filtering is not practical.
Q30. A solution turns phenolphthalein pink. When an acid is added to it drop by drop, what will happen to the pink color?
The solution is basic (since it turned phenolphthalein pink). When an acid is added, it neutralizes the base. As the solution becomes neutral or acidic, the pink color disappears, and the solution becomes colorless. It will not turn blue or yellow.