Question

1. the deposition of ammonium chloride crystals on the walls of a test tube after heating is due to a. evaporation. b. sublimation. c. recrystallization. d. fractional precipitation. 14. the product of decarboxylation of ch₃ch₂ch₂coona is a. propanoic acid. b. propene. c. butane. d. propane. 15. if a heavy metal has an unstable nucleus, the instability could be reduced by i. making neutrons and protons approximately equal ii. increasing its nuclear size iii. making the nuclide undergo decay a. i and ii only b. ii and iii only c. i and iii only d. i, ii and iii 16. the process involved in the production of ethanol from sugarcane is a. esterification. b. neutralization. c. fermentation. d. saponification. 17. which of the following statements about allotropes is correct? a. atoms with different number of neutrons but same number of protons. b. different forms of an element in the same physical state. c. molecules with the same molecular formula but different structures. d. molecules that absorb water vapour on exposure to air. 18. gas x diffuses twice as fast as gas y under the same conditions. if the relative molecular mass of x is 28, the relative molecular mass of y would be a. 120. b. 56. c. 112. d. 14. 19. which of the following gases turns red litmus paper blue? a. co₂ b. nh₃ c. hcl d. so₂

Explanation:

1. Ammonium chloride directly changes from solid to gas and then back to solid on cooling, which is sublimation.
2. Decarboxylation of a sodium - carboxylate salt like $CH_3CH_2CH_2COONa$ removes the carboxyl group as $CO_2$, leaving an alkane. Here, the product is propane.
3. Making neutrons and protons approximately equal and making the nuclide undergo decay can reduce the instability of a heavy - metal nucleus. Increasing nuclear size generally increases instability.
4. Ethanol is produced from sugarcane by the process of fermentation where yeast acts on the sugars in sugarcane to produce ethanol and carbon dioxide.
5. Allotropes are different forms of an element in the same physical state.
6. According to Graham's law of diffusion, $\frac{r_1}{r_2}=\sqrt{\frac{M_2}{M_1}}$. Given $r_X = 2r_Y$ and $M_X=28$, we have $2=\sqrt{\frac{M_Y}{28}}$, so $M_Y = 112$.
7. Ammonia ($NH_3$) is a basic gas and turns red litmus paper blue.

Answer:

1. B. sublimation
2. D. propane
3. C. I and III only
4. C. fermentation
5. B. Different forms of an element in the same physical state.
6. C. 112
7. B. $NH_3$