Chemistry 2017 Jamb Examination

The particle has 9 protons and 10 electrons. Since it has one more electron than protons, it carries a net negative charge. A neutral atom would have equal numbers of protons and electrons, but here the excess electron makes it a negatively charged ion (anion). Therefore, the particle is a negative ion.

In industry, ethene (C₂H₄) is produced by the cracking of hydrocarbons, particularly the thermal or catalytic cracking of alkanes such as ethane or naphtha. This process breaks large hydrocarbon molecules into smaller ones, including ethene. Hence, ethene is obtained by cracking.

Using the ideal gas law:\[PV = nRT\]Given \(P = 6\,\text{atm}\), \(V = 10.5\,\text{dm}^3\), \(R = 0.082\), and \(T = 30 + 273 = 303\,K\).\[n = \dfrac{PV}{RT} \]\[= \dfrac{6 \times 10.5}{0.082 \times 303} = 2.536\,\text{mol}\]Therefore, the amount of gas is 2.536mol.

By Graham’s law of diffusion:\[\dfrac{r_1}{r_2} = \sqrt{\dfrac{M_2}{M_1}}\]\[\Rightarrow \dfrac{t_2}{t_1} = \sqrt{\dfrac{M_1}{M_2}}\]For oxygen (O₂), \(M_1 = 32\); for hydrogen (H₂), \(M_2 = 2\).\[t_2 = 50 \times \sqrt{\dfrac{2}{32}} = 50 \times 0.25 = 12.5\,\text{s}\]Thus, hydrogen takes 12.5 seconds to pass through the plug.

Sodium is highly reactive, especially with water and oxygen, forming sodium hydroxide and releasing hydrogen, which can ignite spontaneously. To prevent this, it is stored under paraffin oil (kerosene) to keep it isolated from air and moisture.

Temporary hardness of water is caused by dissolved calcium hydrogencarbonate, \(\text{Ca(HCO}_3)_2\). When hard water is boiled, it decomposes to produce insoluble calcium carbonate (CaCO₃), which forms scales or 'furring' inside kettles. Hence, furring is caused by calcium hydrogentrioxocarbonate (IV).

Chlorination is a water purification method used to kill pathogenic microorganisms such as bacteria and viruses. It does not remove hardness or colour but ensures the water is microbiologically safe for consumption. Hence, chlorination removes bacteria.

When calcium hydroxide reacts with ammonium chloride upon heating, ammonia gas is liberated along with water and calcium chloride:
Ca(OH)₂ + 2NH₄Cl → CaCl₂ + 2H₂O + 2NH₃
Thus, the gas produced (X) is ammonia, NH₃.

Since \(\Delta H\) is positive, the reaction is endothermic. For spontaneous reactions, \(\Delta G = \Delta H - T\Delta S\). Here, the number of gaseous molecules decreases from 4 to 2, meaning entropy (\(\Delta S\)) is negative. Hence, both \(\Delta H > 0\) and \(\Delta S < 0\) make \(\Delta G\) positive at room temperature, indicating the reaction is non-spontaneous.