Free Bronsted-Lowry and Lewis Concepts MCQs with Answers
26 Bronsted-Lowry and Lewis Concepts MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
The Brønsted-Lowry concept defines acids as proton donors and bases as proton acceptors, producing conjugate acid-base pairs. The Lewis concept extends the idea to electron-pair acceptors and donors, so compounds such as BF3 and NH3 can be treated as acid and base even without proton transfer, unlike the Arrhenius definition.
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26 questions · page 3 of 3
21. Which one of the following is a lewis acid?
- A. (CH3)3N
- B. PH3
- C. BF3
- D. O2
Explanation: The correct answer is BF3 because it is an electron-deficient molecule with the ability to accept electron pairs, making it a Lewis acid. In contrast, (CH3)3N and PH3 are Lewis bases, as they possess lone pairs that can be donated. O2 is neither a Lewis acid nor a base because it is a stable molecule without the capability to accept or donate electron pairs in the context of Lewis acid-base reactions.
Correct answer: BF322. Ka values of some compound are given below, select the correct order of acidic strength:i.H2O ⇌H++OH-Ka=1 x 10^-14 ii. ROH⇌RO-+H+Ka=1 x 10^-18 iii. RCOOH⇌RCOO-+H+Ka=1 x 10^-5 iv.C6H5OH⇌C6H5O-+ H+Ka=1 x 10^-10
- A. ROH> H2O> C6H5OH>RCOOH
- B. C6H5OH > H2O> ROH > RCOOH
- C. RCOOH > C6H5OH > H2O > ROH
- D. RCOOH > ROH > C6H5OH > H2O
Explanation: The increasing strength of acidities is as follows; carboxylic acids, phenols, water and then ethanol. Students should know that carboxylic acids have two electronegative atoms which make the carboxylate anion stable whereas ethanol has positive inductive effect due to the presence of alkyl groups so it is the least acidic. This order is only followed by option C which is the answer
Correct answer: RCOOH > C6H5OH > H2O > ROH23. AlBr3 which is used in the alkylation of benzene possesses the properties of:
- A. A catalyst
- B. A Lewis acid
- C. An electron deficient specie
- D. All of the above
Explanation: AlBr3 is used as a catalyst, it is a lewis acid i.e is an electron-pair acceptor therefore it is also an electron deficient species so option D is correct
Correct answer: All of the above24. Many hexaaqua complex ions can undergo reaction with water as given below[Fe(H2O)6]+2 aq + H2O⇌[Fe(H2O)5OH]+ + H3O+The reaction is classed as:
- A. Redox reaction
- B. Acid base reaction
- C. Substitution reaction
- D. Decomposition reaction
Explanation: The reaction is 'decomposition' as one mole of water is removed to form the hydronium ion
Correct answer: Decomposition reaction25. Which of the following is strongest Lewis base?
- A. Ethylene
- B. Acetylene
- C. Benzene
- D. All have equal strength
Explanation: Acetylene (ethyne) has a triple bond between the carbon atoms, allowing it to donate a pair of electrons more readily compared to ethylene.Therefore, it is the strongest Lewis base among the options given.
Correct answer: Acetylene26. Which one is the strongest conjugate base:
- A. Sulphate ion
- B. Hydroxyl ion
- C. Per chlorate ion
- D. Iodide ion
Explanation: The hydroxyl ion (OH-) is a strong conjugate base. It readily accepts a proton (H+) to form water (H2O). Its strong basicity is due to the presence of a lone pair of electrons on the oxygen atom, which can easily accept a proton. So, when it comes to conjugate bases, the hydroxyl ion is a strong one.
Correct answer: Hydroxyl ion