Q3. Which three products does NCERT name as made from acetaldehyde, besides polymers and drugs?
Acetic acid, ethyl acetate and vinyl acetate (NCERT page 243).
Q4. Formaldehyde is used as formalin, a solution in water, rather than as the pure compound. Use the physical properties in NCERT Section 8.3 to suggest why.
Methanal is a gas at room temperature (NCERT page 235), so it is easier to handle dissolved in water (reasoned), with which NCERT says the lower aldehydes form hydrogen bonds (page 235); beyond the NCERT text, methanal also reacts with water to its hydrate, and a saturated solution holds about 37% by mass (Wikipedia, “Formaldehyde”).
Q5. Taking NCERT’s 40% formalin as 40% formaldehyde by mass, what mass of formalin contains 0.50 mol of HCHO? (C = 12, H = 1, O = 16.)
0.50 mol × 30 g mol−1 = 15 g of HCHO, which is 40% of the formalin: 15/0.40 = 37.5 g (reasoned from NCERT page 243).
Q6. Which aromatic aldehyde does NCERT name for use in perfumes and dyes?
Benzaldehyde (NCERT page 243).