Free Acids, Bases and Salts MCQs with Answers

301. 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

302. 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.

303. 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.

304. Which one f the following has the lowest pH?

• A. 1 M HF
• B. 1 M HCL
• C. 1 m CH3COOH
• D. 1 M NaOH

Explanation: As we know that lower the pH, stronger the acid and greater the no of hydrogen ions in a solution. The acidity of an acid is measured by the ability to remove hydrogen ion.

305. What is the concentration of [H+] in the HNO3 acid solution with a PH of 3?

• A. 3
• B. -3
• C. - antilog [3]
• D. 10^-3

Explanation: pH is defined as the negative logarithm of the hydrogen ion concentration [H+]. Mathematically, it can be expressed as:pH = -log[H+]Rearranging this equation, we get:[H+] = 10-pHSubstituting the given pH of 3 in the above equation, we get:[H+] = 10^-3Therefore, the concentration of [H+] in an HNO3 acid solution with a pH of 3 is 10^-3 M.

306. Milk of magnesia is used for treatment of acidity in stomach, its formula is:

• A. Mg(OH)2
• B. MgSO4
• C. Ca(OH)2
• D. CaSO4

Explanation: Milk of magnesia is a suspension of magnesium hydroxide, with the chemical formula Mg(OH)2. It is an effective antacid that neutralizes stomach acid, providing relief from heartburn and indigestion. The reaction with stomach acid produces magnesium chloride and water, which reduces acidity. The other options, MgSO4, Ca(OH)2, and CaSO4, either have different uses or are not suitable for treating stomach acidity.

307. What is the concentration moles/liter of nitric acid solution having PH of 4?

• A. 0.0001 mol/L
• B. -4
• C. 10-4 mol/L
• D. 10-10

Explanation: To determine the concentration of nitric acid in moles per liter with a pH of 4, we apply the formula: pH = -log[H+]. Rearranging gives [H+] = 10-pH. Substituting pH = 4 yields [H+] = 10-4 = 0.0001 mol/L. Since HNO3 dissociates completely in solution, the concentration of HNO3 is equal to the concentration of H+ ions. Thus, the correct concentration is 0.0001 mol/L.Option B (-4) is incorrect because pH cannot be a negative concentration. Option C (10-4) is mathematically correct but usually expressed as 0.0001 mol/L for clarity. Option D (10-10) would relate to a much higher pH value, unsuitable for this question.

308. If the pH of the solution is 9 its OH− ions concentration is:

• A. 10−5
• B. 5
• C. 10−9
• D. 9

Explanation: As we know that,pH+pOH=14pOH=14-9=5Also, pOH=log[OH-][OH-]=antilog(pOH)[OH]=antilog (5)[OH]=10-5

309. Which is the correct formula of ammonium carbamate?

• A. H2NCONH2
• B. NH4COONH4
• C. H2NCOONH2
• D. NH2COONH4

Explanation: Ammonium carbamate is a salt formed by the reaction of ammonia with carbon dioxide or carbamic acid. It has formula [NH₄][H₂NCO₂].The reaction for its formation is 2NH 3 + CO 2 → [NH 2CO 2][NH 4]

310. Substances dissolved in water react better because :

• A. Water brings them close
• B. Water helps them in bonding
• C. Water dissolve them in ions
• D. Water reacts with them

Explanation: When substances dissolve in water, they often undergo a process called hydration, where the water molecules surround and separate the individual particles of the substance, resulting in the formation of ions. This process is known as dissociation or ionization. Water has a polar molecular structure, meaning it has a slightly positive charge on one end (hydrogen) and a slightly negative charge on the other end (oxygen). This polarity allows water molecules to interact with charged particles (ions) and polar molecules by forming hydrogen bonds.