Chemistry CUET UG 22-05-2023 Shift 3 Paper

Misch metal is a well-known alloy consisting of a lanthanoid metal (around $95\%$, predominantly cerium and lanthanum), iron (about $5\%$), and traces of sulfur, carbon, calcium, and aluminum. Magnesium-based alloys with misch metal are pyrophoric and used in making bullets, shells, and lighter flints.

Comparison of test results:

• 2,4-DNP test is given by all aldehydes and ketones, so both give positive tests.
• Tollens' test is reduced by both aliphatic aldehydes (acetaldehyde) and aromatic aldehydes (benzaldehyde) to form a silver mirror.
• Sodium bicarbonate test is used to detect carboxylic acids, neither aldehyde gives effervescence.
• Fehling's test: Aliphatic aldehydes like acetaldehyde reduce Fehling's solution to give a red precipitate of cuprous oxide ($\text{Cu}_2\text{O}$), whereas aromatic aldehydes like benzaldehyde do not reduce Fehling's solution.

Aspartame is the methyl ester of a dipeptide formed from aspartic acid and phenylalanine. It is about 100 times sweeter than cane sugar. However, it readily hydrolyzes and decomposes at elevated temperatures (cooking temperatures), thereby losing its sweetness. Consequently, its application is strictly restricted to cold foods and soft drinks.

In the MacArthur-Forrest cyanide process for silver extraction:

• Leaching (Oxidation): The crushed silver ore is treated with a dilute solution of $\text{NaCN}$ in the presence of atmospheric oxygen ($\text{O}_2$), which acts as the oxidising agent:
  $$4\text{Ag} + 8\text{CN}^- + 2\text{H}_2\text{O} + \text{O}_2 \rightarrow 4[\text{Ag}(\text{CN})_2]^- + 4\text{OH}^-$$
• Precipitation (Reduction): Zinc dust is added to reduce the dicyanoargentate(I) complex to metallic silver, where $\text{Zn}$ acts as the reducing agent:
  $$2[\text{Ag}(\text{CN})_2]^- + \text{Zn} \rightarrow [\text{Zn}(\text{CN})_4]^{2-} + 2\text{Ag}$$