This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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Step 1: Analyze Question 34. To find the standard EMF of the cell (E^_cell), we use the formula: E^_cell = E^_cathode - E^_anode The half-reaction with the more negative standard electrode potential will be the anode (oxidation), and the half-reaction with the more positive standard electrode potential will be the cathode (reduction). Given: Zn^2+(aq) + 2e^- → Zn(s); E^ = -0.76 V (more negative, so Zn is oxidized at the anode) Cu^2+(aq) + 2e^- → Cu(s); E^ = +0.34 V (more positive, so Cu^2+ is reduced at the cathode) Therefore: E^_cathode = +0.34 V E^_anode = -0.76 V Calculate E^_cell: E^_cell = (+0.34 V) - (-0.76 V) E^_cell = 0.34 V + 0.76 V E^_cell = +1.10 V The correct option is B. B Step 2: Analyze Question 35. The thermal stability of Group 2 carbonates increases down the group. This trend is explained by the decrease in the polarizing power of the cations. As you move down Group 2, the size of the metal cation increases. A larger cation has a lower charge density, which means it has a weaker ability to distort the electron cloud of the large carbonate anion (CO_3^2-). Less distortion of the carbonate ion makes it more stable and less likely to decompose upon heating. A Polarizing power of cations decreases: This is correct. B Atomic size decreases: Incorrect, atomic size increases down the group. C Electronegativity increases: Incorrect, electronegativity generally decreases down a group. D Ionization energy increases: Incorrect, ionization energy generally decreases down a group. The correct option is A. A Step 3: Analyze Question 36. Evaluate each statement regarding nitriles: 1. The functional group in nitrile is -CHO. Incorrect. The functional group in nitriles is the cyano group, -C. -CHO is the aldehyde functional group. 2. Nitriles are prepared by reacting alkyl halides with sodium chloride (NaCl). Incorrect. Nitriles are typically prepared by reacting alkyl halides with potassium cyanide (KCN) or sodium cyanide (NaCN), not sodium chloride. 3. Nitriles can be hydrolysed to carboxylic acids by refluxing with aqueous acid. Correct. Nitriles (R-C) undergo hydrolysis in the presence of aqueous acid (or base) and heat (reflux) to form carboxylic acids (R-COOH). Only statement 3 is correct. According to the directions, if 3 only is correct, choose D. D Step 4: Analyze Question 37. Evaluate each statement for halogens: 1. Reactivity decreases down the group. Correct. As you go down the halogen group (F, Cl, Br, I), the atomic size increases, and the electronegativity decreases. This makes it harder for them to gain an electron, so their reactivity as oxidizing agents decreases. 2. They form diatomic molecules. Correct. Halogens exist as diatomic molecules in their elemental state (e.g., F_2, Cl_2, Br_2, I_2). 3. Fluorine is the strongest oxidizing agent. Correct. Fluorine is the most electronegative element and has the highest standard reduction potential among the halogens, making it the strongest oxidizing agent. Statements 1, 2, and 3 are all correct. According to the directions, if 1, 2, and 3 are all correct, choose A. A Step 5: Analyze Question 38. Evaluate each statement pertaining to buffer solutions: 1. Resist changes in pH. Correct. This is the primary function of a buffer solution. They minimize pH changes when small amounts of acid or base are added. 2. Contain a weak acid and its conjugate base. Correct. An acidic buffer solution is typically composed of a weak acid and its conjugate base (usually in the form of a salt). A basic buffer solution consists of a weak base and its conjugate acid. So, this statement describes a common and essential component of buffer systems. 3. Have pH = 7. Incorrect. Buffer solutions can maintain pH values across a wide range (acidic, neutral, or basic), depending on the specific weak acid/base pair used. Only a buffer designed to operate around neutrality would have a pH of 7. Statements 1 and 2 only are correct. According to the directions, if 1 and 2 only are correct, choose B. B