Chemistry Past Paper PDF

1. Which substance is added to toothpaste to prevent cavities? - A. Fluoride - B. Calcium Carbonate - C. Sodium Chloride - D. Potassium Nitrate 2. What is the main component of baking soda? - A. Sodium Chloride - B. Sodium Bicarbonate - C. Sodium Carbonate - D. Potass...

1. Which substance is added to toothpaste to prevent cavities? - A. Fluoride - B. Calcium Carbonate - C. Sodium Chloride - D. Potassium Nitrate 2. What is the main component of baking soda? - A. Sodium Chloride - B. Sodium Bicarbonate - C. Sodium Carbonate - D. Potassium Bicarbonate 3. What is the main ingredient in bleach? - A. Sodium Hydroxide - B. Calcium Hypochlorite - C. Potassium Chloride - D. Ammonium Nitrate 4. Why are non-stick pans coated with Teflon? - A. Teflon increases heat conduction - B. Teflon is non-reactive and prevents food from sticking - C. Teflon is biodegradable - D. Teflon resists corrosion 5. Which chemical is used in fire extinguishers to produce foam? - A. Sodium Carbonate - B. Potassium Nitrate - C. Aluminium Sulphate - D. Sodium Bicarbonate 6. Why is nitrogen gas used to preserve packaged food? - A. It kills bacteria - B. It is a reactive gas that prevents oxidation - C. It displaces oxygen, reducing spoilage - D. It enhances the flavor of food 7. What is the main chemical used in dry cleaning? - A. Acetone - B. Tetrachloroethylene - C. Ethanol - D. Methanol 8. Which gas is responsible for the characteristic odor of rotten eggs? - A. Methane - B. Hydrogen Sulfide - C. Ammonia - D. Carbon Monoxide 9. Which of the following is used as a desiccant in food packaging? - A. Sodium Bicarbonate - B. Silica Gel - C. Calcium Carbonate - D. Potassium Chloride 10. What happens to water when its temperature reaches 4°C? - A. It expands - B. It freezes - C. Its density is maximum - D. Its density is minimum 11. When sodium metal reacts with water, which products are formed? - I. Sodium Hydroxide - II. Hydrogen Gas - III. Oxygen Gas - IV. Sodium Carbonate - A. I, II, and III - B. I and II - C. II and IV - D. I, III, and IV 12. Which property of soap allows it to remove grease from clothes? - A. Soap forms micelles that trap grease molecules - B. Soap neutralizes grease through chemical reactions - C. Soap breaks grease into smaller particles by oxidation - D. Soap coats grease, making it soluble in water 13. Which among the following reactions is exothermic? - I. Combustion of methane - II. Dissolution of quicklime in water - III. Photosynthesis - IV. Melting of ice - A. I and II - B. I, II, and III - C. II and IV - D. I and IV 14. Why is sodium stored in kerosene? - A. Sodium reacts with air to form toxic compounds - B. Sodium reacts violently with oxygen and moisture in air - C. Kerosene prevents oxidation of sodium - D. Sodium dissolves in kerosene to remain stable 15. Why do we add chlorine to water during purification? - I. Chlorine kills microorganisms - II. Chlorine removes hardness of water - III. Chlorine reacts with organic matter to form safe by-products - IV. Chlorine oxidizes dissolved impurities - A. I and II - B. I, III, and IV - C. I and IV - D. II, III, and IV 16. Why is LPG odorized? - A. To identify leakage easily - B. To enhance combustion efficiency - C. To reduce its density - D. To remove impurities 17. What is the function of alum in water treatment? - I. It kills harmful microorganisms - II. It helps in coagulation of suspended particles - III. It neutralizes acidic impurities - IV. It removes excess salts - A. I and II - B. II only - C. II and III - D. All of the above 18. Why do apples turn brown when cut and exposed to air? - A. Oxidation of natural sugars - B. Reaction of oxygen with polyphenols in the fruit - C. Breakdown of starch into simpler molecules - D. Loss of water content 19. Which chemical is used to preserve biological specimens? - A. Ethanol - B. Glycerol - C. Formalin - D. Acetone 20. Which element is used in the manufacture of safety matches? - A. Phosphorus - B. Sulfur - C. Potassium - D. Magnesium 21. Which of the following statements about hydrogen peroxide (H2O2 ) is/ are correct? - I. It acts as a bleaching agent - II. It decomposes into water and oxygen - III. It is a strong reducing agent - IV. It is used in rocket fuel - A. I and II - B. I, II, and IV - C. II, III, and IV - D. All of the above 22. Why does rust form faster in coastal areas? - I. Presence of salt accelerates corrosion - II. High humidity facilitates oxidation - III. Heat promotes rusting - IV. Water reacts with iron directly in the presence of salt - A. I and II - B. I, II, and IV - C. I and III - D. All of the above 23. What is the chemical formula of plaster of Paris? - A. CaSO4.2H2O - B. CaSO4.1/2H2O - C. CaSO4.3H2O - D. CaSO4 24. What happens when baking soda is heated? - A. It forms carbon dioxide, water, and sodium carbonate - B. It forms only sodium hydroxide and carbon dioxide - C. It decomposes into sodium oxide and carbon dioxide - D. It does not undergo decomposition 25. Which of the following contributes to acid rain? - I. Sulfur Dioxide - II. Nitrogen Oxides - III. Methane - IV. Carbon Dioxide - A. I and II - B. I, II, and III - C. II and IV - D. All of the above 26. Why does milk curdle when lemon juice is added? - A. Acidic juice reacts with casein, causing coagulation - B. The milk proteins undergo oxidation, causing coagulation - C. The lemon juice neutralizes milk fats, forming curds - D. Enzymes in the lemon juice digest milk proteins 27. Why does hard water not form lather easily with soap? - I. Hard water contains calcium and magnesium ions. - II. Calcium and magnesium ions react with soap to form insoluble salts. - III. Hard water has a higher concentration of sulfates and nitrates. - IV. The pH of hard water is always acidic, which inhibits lather formation. - A. I and III - B. I, II, and III - C. I and II - D. All of the above