Acids, Bases and Salts – MCQs with Answers and Explanations
30 Multiple Choice Questions (MCQs) with Answers & Explanations
Each question is followed by the correct answer and a clear, concept-focused explanation to help strengthen understanding. Chemical formulas use <sub> and <sup> tags for accuracy.
Q1. Which ion is produced when hydrochloric acid dissolves in water?
Answer: B. H+
Explanation: HCl ionises in water to give H+ and Cl−: HCl → H+ + Cl−. The H+ (proton) is responsible for acidic properties.
Q2. Which indicator turns pink in a basic solution?
Answer: C. Phenolphthalein
Explanation: Phenolphthalein is colourless in acidic/neutral solution and turns pink in basic solution (transition approx. pH 8.2–10), so it indicates alkaline conditions.
Q3. What is the pH of a neutral solution at 25°C?
Answer: B. 7
Explanation: Pure water at 25°C has [H+] = 1×10−7 M, so pH = −log[H+] = 7, the neutral point on pH scale.
Q4. When zinc reacts with dilute HCl, which gas is evolved?
Answer: C. H2
Explanation: Metal + acid reactions produce hydrogen gas: Zn + 2HCl → ZnCl2 + H2. The hydrogen gas is flammable and can be tested by the pop test.
Q5. Which salt is formed when sodium hydroxide neutralises sulfuric acid?
Answer: B. Na2SO4
Explanation: Neutralisation: H2SO4 + 2NaOH → Na2SO4 + 2H2O. Sulfuric acid is dibasic, so two moles of NaOH are required per mole of acid.
Q6. Which of the following is an amphoteric oxide?
Answer: C. ZnO
Explanation: Amphoteric oxides react with both acids and bases. ZnO reacts with HCl to give ZnCl2 and with NaOH to form complex zincate ions.
Q7. Which indicator is most suitable for titrating a strong acid with a strong base?
Answer: B. Phenolphthalein
Explanation: For strong acid–strong base titrations, the equivalence point is around pH 7; phenolphthalein gives a sharp end point (colourless to pink) and is commonly used. Bromothymol blue may also work; methyl orange is better for strong acid–weak base titrations.
Q8. Which compound is produced when calcium carbonate reacts with hydrochloric acid?
Answer: A. CaCl2, CO2 and H2O
Explanation: Reaction: CaCO3 + 2HCl → CaCl2 + CO2 + H2O. CO2 evolution causes effervescence—an important test for carbonates.
Q9. Which of the following solutions will be basic?
Answer: C. Na2CO3
Explanation: CO32− hydrolyses in water producing OH−, making solution basic. NH4Cl is acidic; NaCl is neutral; HCl is acidic.
Q10. What happens to the pH when an acid is diluted with water?
Answer: B. pH increases (becomes less acidic)
Explanation: Dilution lowers [H+], so pH (−log[H+]) increases towards 7; however, the solution remains acidic if pH remains below 7.
Q11. Which of the following is an acid in aqueous solution?
Answer: B. CH3COOH
Explanation: Acetic acid (CH3COOH) is a weak acid that partially ionises in water to produce H+ and CH3COO−. NaOH is a base, KCl neutral salt, CaO basic oxide.
Q12. Which salt is formed when nitric acid reacts with potassium hydroxide?
Answer: A. KNO3
Explanation: Neutralisation: HNO3 + KOH → KNO3 + H2O (nitric acid + potassium hydroxide → potassium nitrate).
Q13. Which indicator would you choose for titration of a weak acid with a strong base?
Answer: B. Phenolphthalein
Explanation: The equivalence point of weak acid–strong base titration is basic; phenolphthalein changes in that basic range and indicates the end point accurately.
Q14. Which of the following is used as a laboratory method to prepare a pure insoluble salt?
Answer: C. Precipitation
Explanation: Precipitation (mixing two soluble solutions to form an insoluble product) allows collection of the solid salt by filtration—for example, AgNO3 + NaCl → AgCl(s) + NaNO3.
Q15. Which property distinguishes an acid from a base?
Answer: B. Change of litmus colour
Explanation: Acids turn blue litmus red and bases turn red litmus blue. Taste is unsafe as a test; melting point and solubility are not reliable distinguishing tests for acids vs bases generally.
Q16. On adding HCl to Na2CO3, which observation will you record?
Answer: B. Evolution of CO2 gas
Explanation: Na2CO3 + 2HCl → 2NaCl + CO2 + H2O. Effervescence due to CO2 is observed; passing gas through limewater turns it milky.
Q17. Which of the following salts gives an acidic solution in water?
Answer: B. NH4Cl
Explanation: NH4+ is the conjugate acid of weak base NH3 and hydrolyses to produce H+, giving acidic solution. NaCl and KNO3 are neutral salts.
Q18. Which of these is a suitable test for presence of carbonate ions in a sample?
Answer: B. Add acid and test evolved gas with limewater
Explanation: Acid reacts with carbonate to produce CO2, which turns limewater (Ca(OH)2) milky due to CaCO3 formation—classical test for carbonate.
Q19. Which of the following statements is true about strong acids?
Answer: C. They ionise almost completely in water
Explanation: Strong acids like HCl and HNO3 dissociate fully in aqueous solution, producing large numbers of ions and thus showing high conductivity and strong acidic behaviour.
Q20. What product forms when excess chlorine reacts with cold dilute NaOH?
Answer: A. NaClO (sodium hypochlorite)
Explanation: Cold dilute NaOH reacts with Cl2 to produce NaOCl (hypochlorite) and NaCl: Cl2 + 2NaOH → NaCl + NaOCl + H2O. NaOCl is a bleaching/disinfecting agent.
Q21. Which of the following is NOT a product of neutralisation?
Answer: C. Hydrogen gas
Explanation: Neutralisation (acid + base) yields salt and water and is often exothermic; hydrogen gas is produced when acids react with metals, not when acids react with bases.
Q22. Which salt would you expect from the reaction of ammonia (NH3) with hydrochloric acid?
Answer: A. NH4Cl
Explanation: NH3 acts as a base, accepts a proton from HCl forming ammonium chloride: NH3 + HCl → NH4Cl (a white crystalline salt).
Q23. Which statement is correct about methyl orange?
Answer: C. Changes from red to yellow as pH increases
Explanation: Methyl orange is red in acidic medium and yellow in basic; it transitions around pH 3.1–4.4, making it useful for certain titrations.
Q24. Which of the following oxides is acidic?
Answer: A. CO2
Explanation: CO2 forms carbonic acid in water (CO2 + H2O → H2CO3) and is an acidic oxide. CaO and Na2O are basic oxides; ZnO is amphoteric.
Q25. Which of these reactions is exothermic?
Answer: B. Neutralisation of HCl with NaOH
Explanation: Neutralisation reactions are typically exothermic, releasing heat. Dissolving NH4Cl is endothermic; evaporation and melting are endothermic.
Q26. Which salt is produced when nitric acid reacts with magnesium?
Answer: B. Mg(NO3)2
Explanation: Metal + acid → salt + H2. Mg + 2HNO3 → Mg(NO3)2 + H2. The nitrate salt forms when nitric acid reacts with magnesium.
Q27. Which of the following is a method to obtain insoluble salts?
Answer: B. Precipitation
Explanation: Mixing solutions of soluble salts can produce an insoluble salt which precipitates out (e.g., AgNO3 + NaCl → AgCl(s) + NaNO3), enabling collection by filtration.
Q28. What is the basicity of H3PO4?
Answer: C. Tribasic
Explanation: Basicity refers to number of replaceable H+ ions in an acid. H3PO4 has three replaceable protons so it is tribasic.
Q29. Which reagent is commonly used to test for the presence of chloride ions?
Answer: A. AgNO3
Explanation: Adding AgNO3 to a solution containing Cl− gives a white precipitate of AgCl (insoluble), confirming chloride presence: Ag+ + Cl− → AgCl(s).
Q30. Which of the following statements about neutral salts is correct?
Answer: B. They are formed from strong acid and strong base
Explanation: Salts of a strong acid and a strong base (e.g., NaCl from HCl + NaOH) typically produce neutral solutions, because neither ion hydrolyses significantly.
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