Free Acids, Bases and Salts MCQs with Answers

291. Fizzy drinks contain dissolved CO2. The CO2 reacts with H2O to form weak acid which is called:

• A. Acetic acid
• B. Carbonic acid
• C. Lactic acid
• D. Formic acid

Explanation: The weak acid formed when CO2 reacts with water in fizzy drinks is called "Carbonic acid." Therefore, the correct option is "Carbonic acid" as it is the specific weak acid formed when CO2 dissolves in water.

292. Which is strongest acid?

• A. HClO
• B. HClO2
• C. HClO3
• D. HClO4

Explanation: HClO4 (perchloric acid): This acid is the strongest among the options. It is a highly corrosive and reactive acid. Perchloric acid is a strong oxidizing agent and is used in laboratories for various purposes. Therefore, the correct answer is "HClO4" (perchloric acid) as it is the strongest acid among the given options.

293. A metallic oxide when added to water would most likely form an

• A. Base
• B. Acid
• C. Salt
• D. Basic anhydride

Explanation: Metallic oxides that are basic will react with water to form a basic solution. For example, sodium oxide (Na2O) reacts with water to form sodium hydroxide (NaOH), a strong base. Therefore, the most likely product formed when a metallic oxide is added to water is a base.

294. Acids are classified as monoprotic or polyprotic which of the following is a polyprotic acid?

• A. CH3CO2H (aq)
• B. HOCl (aq)
• C. HCHO2
• D. H2CO3

Explanation: H2CO3 is a polyprotic acid. It can donate two protons in separate dissociation reactions: H2CO3 ←→ H+ + HCO3- HCO3- ←→ H+ + CO32- These dissociation reactions show that carbonic acid can donate two protons sequentially, making it a polyprotic acid.

295. A nucleophile is

• A. Lewis acid
• B. Bronsted acid
• C. Bronsted base
• D. Lewis base

Explanation: A nucleophile is a chemical species that donates an electron pair to form a new chemical bond. It is characterized by its electron-rich nature and its ability to participate in nucleophilic reactions. In Lewis acid-base theory, a nucleophile is considered a Lewis base, as it can donate electrons to form a coordinate covalent bond.

296. Which of the following ions can act as a Bronsted acid and base in water?

• A. HCO-
• B. CN-
• C. NO3-
• D. PO4-

Explanation: The HCO- ion can act as a Bronsted acid by donating a proton to a water molecule, forming H2CO3. It can also act as a Bronsted base by accepting a proton from water, forming H2O and CO32-.

297. Which of the following can function as Lewis acid?

• A. CN-
• B. NH3
• C. CH3 - O - CH3
• D. I+

Explanation: The correct answer is I+. A Lewis acid is defined as an electron pair acceptor, and I+ fits this definition because of its positive charge and incomplete octet, making it electron-deficient. This allows it to accept electron pairs from Lewis bases. Other options, such as CN-, NH3, and CH3 - O - CH3, are more likely to donate electron pairs due to their lone pairs or negative charge, making them Lewis bases instead.

298. 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.

299. 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

300. 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